[FT] xDevs.com KX LTZ1000A fairy-tale, or the story of little jumper. - Page 1
Forum section: electronics / general

author: TiN
author_rank: Super Contributor
timestamp: October 18, 2016, 04:53:05 am
content: Let's start the new segment, fairy-tales of metrologyIntroOne of engineers doing precision measurement projects at home for own enjoyment contacted me while ago, asking some questions related to nanovolt-meter amplifier front-end and voltage references. His country of residence is Belarus, and I mention this because their customs are really strict about international shipments. Basically everything over 20 $USD mark is troublesome to import and due to high fees, often much more than package value itself. So his instrumentation desk was mostly using some old instruments, made in Soviet Union. We had nice talk about electrometer of his, which is an interesting bit of gear on its own.On DMM front he has Datron Model 1271, 7½-digit DMM, smaller brother of Model 1281 which our other contributor, Todd, had covered well before. Quickly talk was biased towards voltage references. Buying famous Linear LTZ1000 was not an easy option due to shipping/customs troubles, even worse considering existing lack of access to calibrators or metrology labs nearby. Even though this 1271 is fine instrument, it was not recently calibrated and absolute accuracy was unknown. Since this situation was very familiar for me few years ago, I decided to give a hand and help this engineer to “import” verified DCV standard into his home hobby lab. Agreement to build one KX LTZ1000 voltage reference was made.Buy some parts, put on PCB with less than 30 components, measure the output and send the board thru mail. Sounds easy job, no rocket science, right?Parts source and assemblyTo make this whole little project more interesting for me, I wanted to try two new ideas, which were not attempted before in previous builds.*A.* Try 1K?/13K? hermetic resistor network (customVishay VHD200, oil-filled +/-3ppm/K two-resistor network) with 0.05% matching. This might give some interesting data, if tightly coupled oven setting thermal point resistors help to improve tempco of the reference.*B.* Try alternative chopper amplifier, Analog Devices ADA4522-1. Usually I use LTC2057, but both op-amps are rather overkill for this particular circuit, as noise of LTZ1000 zeners itself is magnitudes higher than opamp contribution. But maybe other issues pop up with AD chip. Let's see.As a base my latest Rev.B02 version ofKX LTZ1000 PCBis used. This module 4-layer FR4 ENIG-plated PCB use two single op-amps in SO-8 package, accepts +10-20VDC inputBefore soldering resistors down into circuit, I did a quick measurement to check that they don't give some wild deviations.Custom VPG 120 ?, R3 ,-0.8 ppm - +26.4 C, 0.36 ppm/KVPG VHD200 1 K?, R4 ,-75 ppm - +24.0 C 2.5 ppm/KVPG VHD200 13 K?, R5 ,-5 ppm - +24.3 C 1.4ppm/KFirst small SMD parts were soldered on, and checked. Used LTZ1000ACH chip, manufactured 36 week of 1993 was soldered on, with maximum soldering time around 0.5 second per pin, to reduce excessive heating. Foil precision resistors were populated last. Assembled module ready for the initial test.Before we jump in to actual test data, it's important to have good confidence in measurement equipment and lab tools, to make sure that any unexpected phenomenon comes from device under test, not the equipment itself. This also means that even brand new, freshly calibrated equipment must be verified and tested before any solid conclusions to be made.To satisfy this requirement, I had chance to calibrate my older LTZ1000ACH/LTZ1000CH based references against 15-day calibrated Fluke 732B DC Voltage standard in mid-August 2016. Two Keithley 2002 8.5-digit multimeters we calibrated to same Fluke reference same time, to act as transfer standards and guard-banding tools. I used these DIY standards and DMMs to transfer absolute DCV voltage into myverified and improved HP 3458A, which confirmed to be stable by daily 24/7 operation and monthly checks to both hot and cold external LTZ1000A modules. As a result, I have high confidence that absolute DCV accuracy in my home lab is within +/-2 ppm.Now with verified gear, initial test conditions are fairly simple. Purpose of first test is to make sure of reference normal operation, and measure initial voltage, drift if any and stability. Output should not deviate more than +/-1 ppm over few days period, and temperature coefficient (change of output voltage from change of ambient temperature) should not exceed +/- 0.1 ppm/K.Power supply : 12VDC 2A cheap mains power brick.Measurement : HP 3458A, calibrated August 31 to +/-2ppm DCV.Ambient condition : Ambient room temp with aircon, +/-3 C. Monitor byBME280 sensorDatalogging :Raspberry Pi with linux-gpib+ python +NI GPIB-USB-HSAnalysis :D3.js plotting libraryon xDevs.com siteTest 1Yes, it's alive, measuring output voltage +7.067329 VDC +/-2 ppm.And how we looking here? If this would be integrated reference, such as band-gap reference on internal DAC/ADC references, result noise 1.1 ppm could be simply miraculous. However for top-end ovenized buried zeners, which for Linear LTZ1000 is extremely bad. To remind you specifications, this circuit should be able to provide 0.05 ppm/K drift rate and approximate noise levels of 1.2 uVpk-pk. We are getting 7.4 uV instead for noise. Tempco is also horrible, about 1 ppm/K, 20 times worse than expected!Test 2: TC correction resistor addFor second test we work on mistake and try to address issues on data we saw earlier.* Improve stability of ambient temperature, so we can isolate TC issue for now.* Test with 394K R2 populated, even though we use LTZ1000ACH and this compensation not needed.Some of our readers not familiar with LTZ1000 performance may scream at me right now, how you know that this is bad result. Vertical ppm scale (left green scale is +/-1ppm, which is 0.0001% accuracy!) is blown out to make this amazing reference look bad, you say?Alright, I hear you. And here's the answer, same condition measurements with good and checked LTZ1000CH voltage reference module, using same schematic and same PCB, just different parts. Horizontal time span of graph below is 11 hours.Reference test result on another LTZ1000CH KX moduleSee, noise of this good module is mere +/-0.1ppm, no random jumps or other weird crap, everything nice and stable. That's how you want it, not jumpy-jumpy. Of course if you reduce your accuracy demands to 0.002%, everything looks nice even with jumps.But it does not make sense to pay 250$ USD for such accuracy, so let's continue our journey.Test 3: Reduction of oven temperature testAlright, how about reduce LTZ1000ACH oven temperature inside chip, by changing 13K? resistance on divider to lower value? Let's seeFluke 300K? -1 ppm/K wirewound resistor was soldered in parallel with 13K? on board, and test was repeated.Test 4: Op-amp kelvin connection testHere I had cut separate trace between Pin 2 U5 opamp and R6 resistor, and jump-wired connected guard ring point directly at pin 4 of LTZ1000ACH chip. This makes almost Kelvin-like connection for all inverting node connections. Why I did so? Hm, intuition?Jumpie-jumpie is still there. Noise of LTZ chip noise itself is riding on top of those jumps. Overall it looks nice and stable, just the pesky jumps, which is pink-noise of zener junction. Output voltage changed from +7.064808 to +7.066329 VDC, which is +215 ppm.Test 5: Replacement of LTZ1000 chipNow, if we dig a bit into physics, this jumps are nothing but pink-noise, likely caused byzener effect breakdownis due to quick bursts of electrons going thru thin junction on high voltage. This breakdown is just about 7 volts, and that's close to out near 7.06V output of zener inside this LTZ1000ACH. So it does look that no external component tweaks could fix this... Let's see on test result of TEST RUN 5:t's good now! What is the magic? There is none, actually, just engineering. Now we getting some solid data. Noise over multiple hours is just around 0.2ppm, which translates into around 1.2 uV[~pk-pk~], initial tempco evaluation from +26.6 C to +30.5 C unable to reveal any tempco clearly, no large jumps either.BonusI also built thermal box to test tempco, so jump into full article link down belowTotal amount of time for this project~25 hours, including~50 hoursof datalog time by HP 3458A.Hope this data helps to better understand hidden icebergs and dangers big enough to sink a project in high-precision field, even for something as simple as direct voltage reference module. It's not enough to buy fancy parts and plonk them on the board to get 1 ppm accuracy.I have it running tempco test now, from 20C to 55C in 0.1C per hour step.Full articleIf you have own unexpected story, do tell us.Important update, calibration offer by communityOne of our members,mimmus78ordered KX LTZ1000 PCBs and sent some to other interested tinkerers at cost, so to support this great initiative, additional "calibration service" is provided by me,plesaandAlex Nikitinto support this.Rules to participate are simple:STEP 1. Build your KX-module, publish short worklog in this thread (few photos of assembled PCBA, photo of it running with DMM hooked up showing 7V)STEP 2. Leave it running for 200 hours, so initial drifts get stabilized. Module should be enclosed in some box without vents.STEP 3. Measure it again, record the temperature and voltage and put a label with values on the boxSTEP 4. Ship the box to me (Taiwan) or other member (Europe) after agreement via EEVBlog PM. You pay shipping.STEP 5. I'll power your box with +15V for 48 hours to have everything stabilizeSTEP 6. Test 7V output voltage in temperature span +20....+30C, record the graphSTEP 7. Unit will be shipped back (from me via EMS Express (~30-40$USD, 4-7 days to USA, bit more to EU)). You pay shipping.All steps are mandatory, to make sure that reference is good and stable, otherwise it would be no much point in ppm-level calibration, if initial aging drifts are not removed first.This is standing offer, without schedule or specific date deadlines, unless my homelab changes or other force majeure events occur.Even though I don't have official calibration performed on my equipment, thanks to volt-nut community and multiple cross-checks I'm confident that my DCV accuracy is around &plusmn;2 ppm.And to make this even better, few other EEVBlog members also backed up this initiative to provide same calibration offer in their regions.Calibration byAccuracy / StandardRegion/CountryContact for participantsxDevs.com<2ppm / 3458A-mod + 2*K2002Asia/TaiwanEEVBlog forum PMplesa<4ppm / 3458A-002Europe/SwedenEEVBlog forum PMAlex Nikitin<4ppm / 3458A-002Europe/UKEEVBlog forum PMArticle was also updated for same information

author: lukier
author_rank: Unknown
timestamp: October 18, 2016, 08:15:13 am
content: Interesting story.I would thought that such expensive parts go through rather stricter testing (than TL431 for example). I remember in your 3458A article the original reference board from eBay also had jumpy LTZ1000.Is this jumpy LTZ1000 brand new or second hand from eBay?Slightly worrying, as I would like to build a LTZ1000 reference at some point, but no way I'm buying a dozen chips or so to find one working to the specs

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: October 18, 2016, 08:52:01 am
content: This jumpy LTZ was the one from the A9 board that TiN bought on flebay for is 3458.The resolution is in the full article in TiN's website, he then replace the LTZ with another one and no more jumps.

author: TiN
author_rank: Super Contributor
timestamp: October 18, 2016, 09:08:17 am
content: lukierI think you get answers from article. If it's more comforting, all 6 LTZ chips I bought directly from Linear site are not jumpy.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: October 18, 2016, 09:19:05 am
content: Quote from: TiN on October 18, 2016, 04:53:05 amTiN do you notice any diference yet, with the exchange of the voltage divider in relation to previous method, of two independent resistors?This way the tracking of Tempco should be better since they are inside the same encapsulation.BTW, in a conversation with Edwin Pettis he told me, that the Engineers from LT told him that for the last few years they recommend the all LTZ's to be drive by 15K/1K, but this was already cover in the LTZ thread .

author: lukier
author_rank: Unknown
timestamp: October 18, 2016, 10:37:48 am
content: Quote from: TiN on October 18, 2016, 09:08:17 amOh got itI thought that's yet another unit, so I worried about LTZ1000 reliability.

author: zlymex
author_rank: Frequent Contributor
timestamp: October 18, 2016, 11:47:37 am
content: Good story and nice photos/charts. Slightly worrying for me too because I did not test all of my 2nd hand LTZ1ks fully.TiN is the thermistor hermetic? It seems to be very stable over time.

author: TiN
author_rank: Super Contributor
timestamp: October 18, 2016, 12:22:38 pm
content: zlymexIt's teflon coated. You can see photo of it in the article. Overall it does look more stable than my previously used Honeywell HEL-705 Pt RTDs (on same K2510 setup). I had to increase current for RTD at 833uA compared to just 100uA on this YSI 44031.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: October 18, 2016, 01:52:44 pm
content: One time I was repairing Data Precision 8200 DC calibrator.I did many measurements to prevent good old precision components from heating during soldering.Unfortunately the problem was LM399 (see plot).Maybe it is a problem with contact resistance inside IC.I assume that Data Precision would not release a product with such issue, so it is very likely that this LM399 broke down during normal use.

author: VintageNut
author_rank: Frequent Contributor
timestamp: October 18, 2016, 02:04:16 pm
content: I have been monitoring one of my Fluke 731B for a few days continuously with a DMM7510 on 15 NPLC with averaging of 10. In the morning the measured voltage is 9.999961 and late evening the voltage is 9.999978. This cycle is consistent from day to day. At first I thought it was temperature but after some colder weather followed by warmer weather, I think the cycle is humidity.I have no humidity measurement equipment now so that has to be on the list to obtain sooner than later.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: October 18, 2016, 02:24:56 pm
content: For humidity, pressure and temperature I think that the BME280 is hard to beat. And you can do like TiN, sample it together with your measurements via GPIB.

author: zlymex
author_rank: Frequent Contributor
timestamp: October 18, 2016, 02:41:10 pm
content: Quote from: VintageNut on October 18, 2016, 02:04:16 pmThen you need a third equipment to judge, either a DMM or a voltage reference,

author: TiN
author_rank: Super Contributor
timestamp: October 18, 2016, 05:15:34 pm
content: Or send that 7510 to us for check3458 vs 7510... I think that's not equal fight

author: Kleinstein
author_rank: Super Contributor
timestamp: October 18, 2016, 06:40:43 pm
content: The Fluke731 and DMM7510 should have a similar class reference inside. So it could be either one that is doing the drift.The reference in the 3458 is not better than that, and near full scale is could be very well the reference that sets the limitation. So 3458 vs DMM7510 would be LTZ1000 vs LTFLU so this may come down to binning or individual quality.

author: VintageNut
author_rank: Frequent Contributor
timestamp: October 18, 2016, 06:57:48 pm
content: Good points Tin. I will connect my model 2000 in parallel with the 7510 and let it run for a few days to see if the drift is detectable on the 2000 as well.I am reasonable certain that the drift is the 731B but only proper measurements and analysis of the data will make it certain.I accept the challenge to find out for sure.Do you collect your data for this type of analysis with Python?

author: Andreas
author_rank: Super Contributor
timestamp: October 18, 2016, 07:09:31 pm
content: Quote from: TiN on October 18, 2016, 09:08:17 amHello Illya,You have to look harder on the noise.My LTZ#5 has relative large jumps of typical 1uV up to 1.8uV.The others have also jumps (below the 1.2uVpp) which are only visible when zooming into the record.E.g. LTZ3 with a 300nV jump.All my LTZs are sourced via distributor or DigiKey.So even if they are costly you have to monitor them for popcorn noise.The noise screening tests at the manufacturer typical use a very short time window.(<< 10 seconds)So the detection of popcorn noise is usually not possible.With best regardsAndreas

author: Theboel
author_rank: Frequent Contributor
timestamp: October 18, 2016, 11:46:21 pm
content: I am sorry Ilya and others if this not relevant but anybody has experience about same jump/popcorn noise from LM399 ?

author: d-smes
author_rank: Regular Contributor
timestamp: October 19, 2016, 10:32:00 am
content: Quote from: Nuno_pt on October 18, 2016, 09:19:05 amIs this new info? I thought you only wanted to run them that hot for the "A" version in high ambient environment. Can you link to where this recommendation was discussed? I skimmed through the LTZ1000 thread but couldn't find it...

author: TiN
author_rank: Super Contributor
timestamp: October 19, 2016, 10:38:52 am
content: The choice is up to application. Lower noise at cost of long term stability - run high temp. Better long term stability (thats what most people here after) at cost of noise - reduced temp.

author: TiN
author_rank: Super Contributor
timestamp: October 19, 2016, 10:59:20 am
content: Also I realized something this morning during my ride to work.Since now I have bad, but functional LTZ1000A chip, which I'd not really use in voltage reference builds, it opens a road to second fairy-tale...We don't really care if it dies, right? Now if I can find LTZ-set resistors which I can sacrifice without breaking a bank, we can make one special module to run cryotest.That is, enclose module into metal box with weak thermal coupling and submerge everything into fresh 26L dewar with LN2, without heater circuit on.It could answer question I was asking myself for years, if LTZ1000 at 77K can deliver better than 0.1ppm noise. If it's positive, then that would open new box of pandora making cooled LTZ-references.LN2 is also cheap, so that experiment could be repeated by other volt-nuts if proven worthwhile (for example to do nV LNA testing, when lowest noise possible is a help).Why need sacrifice resistors? Because they are unlikely to be very good and stable after 230K thermal shock.

author: VintageNut
author_rank: Frequent Contributor
timestamp: October 19, 2016, 12:02:36 pm
content: Have you placed one of these reference boards in an ordinary freezer at 0 deg F to test the idea?

author: TiN
author_rank: Super Contributor
timestamp: October 19, 2016, 12:32:01 pm
content: I'd expect difference at 0 would be just down in measurement errors and uncertainty.

author: VintageNut
author_rank: Frequent Contributor
timestamp: October 19, 2016, 03:09:14 pm
content: Quote from: TiN on October 19, 2016, 12:32:01 pmDoes the noise reduction only happen at some magic very low temperature or is the noise reduction a linear function of temperature?

author: TiN
author_rank: Super Contributor
timestamp: October 20, 2016, 04:04:42 am
content: Delta deviation in ppm per each °C is shown on graph.Also for easier grasp, here's summary data on chamber temperature span from +16 °C to +31 °C (temperature stability +/-0.005 °C). Perhaps bit easier on table below with calculated temperature coefficient and output deviation delta in ppm units. Voltage reading at +16.000 °C was taken as a baseline.As we can see, temperature coefficient stays very close to +/-0.05 ppm/K specification. Also one has to remember than this test is essentially a comparison of internal HP 3458A LTZ1000-reference versus external. So accuracy of such measurements is already +/-0.1 ppm at best. To perform better measurement, one would need measurement equipment more stable than old aged HP 3458A, which leaves very few options, like very expensiveJJA systemsor characterized bank of Fluke 732A/732B/734A DC standards and low-noise null-meter.RAW samples data in DSV-format is available as well, if you reader desire to conduct own analysis.DSV-data log with temperature chamber testI still have it running to raise temperature up to 50 °C, so will update data after test samples arrive

author: Cerebus
author_rank: Super Contributor
timestamp: October 26, 2016, 01:04:09 am
content: Quote from: DiligentMinds.com on October 19, 2016, 04:28:54 pmThis is worth emphasising because a lot of people miss this. Internal to the LM399 is an, internally regulated, constant current supply that pushes 250 uA through the zener. Any excess current is shunted off by a pair of transistors that just turn the excess into heat. This doesn't mean that you can get away with feeding the LM399 with an unregulated current but you won't gain anything by going over the recommended 1 mA.

author: mimmus78
author_rank: Unknown
timestamp: October 27, 2016, 03:27:45 pm
content: Hi TiN,do you still have some of this PCB unpopulated?Thanks,Domenico

author: TiN
author_rank: Super Contributor
timestamp: October 27, 2016, 03:40:49 pm
content: Hi,I have two left, but I need them for few items in near future. Somebody here is waiting for fab using my gerbers, I believe.Btw, I done log with K2001 for you, but have no time recently to make pretty graph.Live graph and RAW data is here. Plenty of data there to run STDEV, noise pk-pk analyze and such. K2001 column is k10v.

author: plesa
author_rank: Frequent Contributor
timestamp: October 27, 2016, 05:08:09 pm
content: Quote from: TiN on October 27, 2016, 03:40:49 pmI have 4 TiN boards, but all populated. All are currently measured with recently calibrated 3458A/002.

author: TiN
author_rank: Super Contributor
timestamp: October 27, 2016, 05:19:44 pm
content: plesaHow's your datalogging setup going on? If you wish, I can give you space on my serv and script, so your Pi can upload CSVs periodically and I can have live plot page for you

author: plesa
author_rank: Frequent Contributor
timestamp: October 27, 2016, 06:24:27 pm
content: Quote from: TiN on October 27, 2016, 05:19:44 pmThanks I already have local website on RPi2 which use also thehttps://d3js.org/for graphs.It is quite amazing, BME280 will be connected soon for environment logging.

author: TiN
author_rank: Super Contributor
timestamp: October 27, 2016, 06:26:03 pm
content: I'd love to see some data too

author: mimmus78
author_rank: Unknown
timestamp: October 28, 2016, 08:25:07 am
content: Thanks TiN ... noise is identical.Anyway just ordered 20 pcb of your project, if someone needs some I have few spares.

author: pelule
author_rank: Frequent Contributor
timestamp: October 28, 2016, 09:19:51 pm
content: @ mimmus78QuoteJust to be sure, I have the right "project" in mind. Does you have ordered this?https://xdevs.com/doc/xDevs.com/KX_STR/top.jpgIf so, I would be interested into 2 to 4 boards.

author: mimmus78
author_rank: Unknown
timestamp: October 29, 2016, 08:25:04 am
content: Well I ordered 20 PCB. I will keep 3 for me and the rest I can sell. I will actually build only one kit, I don't think I will use more than 3 pcb because this kit will cost more than 300 EUR.I spent 160 EUR per the 20 pcb included express shipping and slow fabrication. So it's 8 EUR + shipping for one.Shipping for PCB will be done by registered mail. Usually it takes 10 days for US and one week for europe.I will not do DHL/UPS shipping because this will require customs declaration and invoicing that I really don't like to do.I asked for a quote to vishay for restors just for myself... but maybe we can group buy also this resistors (here is 60%~ of kit costs).Unfortunately shipping those 200 EUR worth of resistor cannot be done by standard mail ... so it may turn out not so convenient.As in the other thread, if you like to have some pcb just add your name to the list.Mimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcs==================================Remaining Boards: 8pcs

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: October 29, 2016, 08:31:58 am
content: There is no need for the Vishay VHP, you can use UXB, UPW20/50 or from Edwin, 0.1% 3ppm/C°

author: klaus11
author_rank: Unknown
timestamp: October 29, 2016, 09:32:49 am
content: Así que pedí 20 PCB. Voy a seguir 3 para mí y para el resto puedo vender. De hecho, me construiré un solo kit, no creo que voy a utilizar más de 3 PCB ya que este kit tendrá un costo de más de 300 euros.Pasé 160 euros por el 20 de PCB, con el envío expreso y fabricación lento. Por lo que es de 8 euros + gastos de envío para uno.Envío de PCB se hará por correo certificado. Por lo general, se tarda 10 días en los Estados Unidos y una semana para Europa.No haré el envío de DHL / UPS, porque esto requerirá declaración de aduanas y la facturación que realmente no me gusta hacer.Pedí una cita para Vishay para restors sólo para a mí mismo ... pero tal vez podemos agrupar comprar también esta resistencias (en este caso es del 60% de los costes ~ kit).por desgracia envío de los 200 euros de resistencia no se puede hacer por correo ordinario ... por lo que puede resultar no tan conveniente.al igual que en el otro hilo, si le gustaría tener un poco de PCB sólo tiene que añadir su nombre a la lista.Mimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcs================= =================restante Juntas: 6pcs

author: VK5RC
author_rank: Unknown
timestamp: October 29, 2016, 10:49:06 am
content: I would like 3 if available stillMimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcVK5RC ;3pcs

author: t2kv
author_rank: Contributor
timestamp: October 29, 2016, 10:57:05 am
content: And I'd like two if they're still available, please:Mimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcVK5RC ;3pcst2kv: 2pc

author: HighVoltage
author_rank: Super Contributor
timestamp: October 29, 2016, 11:39:51 am
content: If there are any left, I take 2 pieces, thanksMimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcVK5RC ;3pcst2kv: 2pcHighVoltage: 2pcs

author: mimmus78
author_rank: Unknown
timestamp: October 29, 2016, 02:21:41 pm
content: High voltage we are one out ... if they send me some more board no problem.

author: David Hess
author_rank: Super Contributor
timestamp: October 30, 2016, 02:13:01 am
content: It looks like a classic case of popcorn noise and not pink noise. The level is awfully low and I cannot say that I have seen popcorn noise in a zener diode but the base-emitter transistor junction in series with the LTZ1000A zener could be responsible and combined with the low impedance at the collector would explain the low level.Screening for popcorn noise is very difficult because of its often intermittent nature. Long test times, hours to days, make it economically impractical for most customers. I thought I remembered a note from LT about screening LTZ1000s for something but I looked and did not find it.

author: Cerebus
author_rank: Super Contributor
timestamp: October 30, 2016, 03:09:32 am
content: Quote from: David Hess on October 30, 2016, 02:13:01 amAgreed that it looks like popcorn noise, but I think the explanation is wandering between zener and avalanche modes. Intrinsic to these low TC zeners is the balancing of the opposite tempcos of zener and avalanche effects. I think that's already been suggested hereabouts as a cause but I'm not sure. Popcorn noise is classically associated with relatively 'dirty' semiconductor processes which is why it's generally much less of a problem than it was, say, thirty years ago. We're dealing with a buried zener here, and the burying is done precisely to keep the junction away from the surface where impurities may lurk of the sort that cause popcorn noise.

author: David Hess
author_rank: Super Contributor
timestamp: October 30, 2016, 06:04:07 am
content: Quote from: Cerebus on October 30, 2016, 03:09:32 amThe buried zener in this case is temperature compensated by the roughly -2mV/C Vbe of a series transistor so I am suggesting that the popcorn noise is actually coming from the transistor and not the buried zener reference.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 30, 2016, 08:16:26 am
content: The popcorn noise could come from the zener or the transistor - hard to tell from the data.One could modify the circuit a little and compare the jumps. If the noise is sensitive to the zener current, this would indicate the zener as a source, if it changes with the transistor current it is likely coming from the transistor. The nice thing about the LTZ1000 circuit is than one change the currents relatively independent.Even with that level of noise the reference might still be useful - maybe a a "two value" reference. The problem would only be if the popcorn noise gets slower and one gets only one level over a longer time - you than never know if it is the upper or lower level. So the preferred way would be to reduce the size of the jumps, not making the jumps less frequent - this could make thinks worse, even if you don't see the jumps anymore.I don't see much sense in cooling and that way possibly destroying the chip. One might even think about using it for RMS conversion instead.

author: TiN
author_rank: Super Contributor
timestamp: October 30, 2016, 08:23:11 am
content: QuoteThat's assuming both levels not change over time.QuoteI don't see either, but desired to close this topic once and for all. Maybe we could see something in doing this (not necessarily at 77K temperature). Having 24/7 cooled to -30°C unit with TEC or phase-change loop (modified window AC) isn't that difficult, if there is point in it. I've ordered copper block at CNC shop to enclose module in hermetic box to place in dewar. This way there will be less rapid shock from contact with cooling liquid.

author: Cerebus
author_rank: Super Contributor
timestamp: October 30, 2016, 12:52:23 pm
content: Quote from: David Hess on October 30, 2016, 06:04:07 amYes, the LTZ is using VBEcompensation (and a lot of heat) rather than relying on zener versus avalanche tempco, but the zener versus avalanche thing is still going on because that's determined by the diodes 'set point*' voltage. I'm just influenced by the fact that there's some identifiable physics that we know goes on around this point. Anyway, the only way to be sure is to try the zener current versus transistor current experiment that's been suggested.*Awkward terminology here because you'd normally say "zener voltage" or "avalanche voltage" but both are in play.

author: David Hess
author_rank: Super Contributor
timestamp: October 30, 2016, 11:30:21 pm
content: Quote from: Cerebus on October 30, 2016, 12:52:23 pmAs you pointed out, the zener is buried to prevent exactly this sort of problem. I did a search but found nothing about popcorn noise in zener diodes which may just mean that it is such a minor problem that it takes an LTZ1000 before it becomes apparent since zeners are so noisy anyway. I thought I remembered a comment from LT about special screening options for the LTZ1000 which included low frequency noise but was not able to find it. In transistors, it is usually more apparent because of transistor gain but in this case, the low impedance collector load limits gain.Since access is provided to the node between the buried zener and transistor base and actually every terminal of the transistor, testing to find the source is straightforward if not easy.Tracking down popcorn noise was my motivation for expanding my collection of Tektronix oscilloscopes to include the 7A13 (1mV/div), 7A22 (10uV/div), and AM502 (10uV/div) differential vertical amplifiers. It took me weeks to track down the example shown below because of its low level and especially intermittent nature where it was clean for hours at a time.

author: Andreas
author_rank: Super Contributor
timestamp: October 31, 2016, 07:45:07 am
content: Quote from: David Hess on October 30, 2016, 11:30:21 pmHello,according to Warren they formerly selected 1N82x Zeners according to low frequency (= popcorn?) noise.https://www.febo.com/pipermail/volt-nuts/2013-January/002362.htmlsee also attachement with a chart recorder.http://www.febo.com/pipermail/volt-nuts/attachments/20130126/1fdc1ce7/attachment-0001.jpgOn another source I have read that ageing of zeners is correlated with low freqency (popcorn?) noise.(which makes sense if you equal "popcorn noise" with "impure silicon").With best regardsAndreas

author: fanOfeeDIY
author_rank: Unknown
timestamp: October 31, 2016, 08:49:20 am
content: Hi mimmus78,Thank you, if there is still left.Mimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcVK5RC ;3pcst2kv: 2pcHighVoltage: 2pcsfanOfeeDIY: 2pcs

author: David Hess
author_rank: Super Contributor
timestamp: October 31, 2016, 09:35:59 am
content: Quote from: Andreas on October 31, 2016, 07:45:07 amUnfortunately I do not think the post really tells us anything. Temperature compensated zener diodes like the 1N821 to 1N829 series include a forward biased PN junction in series just like the LTZ1000A and for the same reason so the popcorn noise still could be coming from either.Popcorn noise is low frequency but the post confuses it with 1/f noise as well and the graph in the post shows 0.033ppm versus the 0.5ppm that TiN recorded. Does that indicate two different sources or could it just be that the transistor in the LTZ1000A is amplifying it? I wonder what the difference in time scale means if anything.Isn't the connection between zener aging and popcorn noise simply because it takes time to detect?

author: mimmus78
author_rank: Unknown
timestamp: November 07, 2016, 02:06:52 pm
content: Hi everybody,pcb were fabricated and are now travelling to my home.I should receive it tomorrow or Wednesday.I will post PCB photo here when they arrive.Ciao,Domenico-------------------------------------------------------------------------------------------------------------Mimmus78: 3pcsNuno_pt: 3pcsmsliva: 3pcspelule: 3pcsklaus11: 2pcVK5RC ;3pcst2kv: 2pcHighVoltage: 2pcsfanOfeeDIY: 2pcs

author: Echo88
author_rank: Frequent Contributor
timestamp: November 07, 2016, 02:22:46 pm
content: Damnit, havent seen that you sell these LTZ-PCBs here. Is there still one left for me to buy?

author: mimmus78
author_rank: Unknown
timestamp: November 08, 2016, 08:57:39 am
content: Echo88, I don't think soo ... I already have some overbooking.PCBs will arrive today.

author: mimmus78
author_rank: Unknown
timestamp: November 08, 2016, 01:53:08 pm
content: PCB arrived. They screw up couple of ring guard.What we do? Do I have to ask for a refabrication or we keep as is?One point they forget to remove soldermask. Other two points they leaved ring guard open by cutting the track.Here attached sono photo.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: mimmus78
author_rank: Unknown
timestamp: November 08, 2016, 09:54:55 pm
content: Hi guys here are problems with those PCB I received today.If for you is OK I will ask to fab to redo the lot.Let me know what you think.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: November 08, 2016, 09:58:57 pm
content: Let's see what more experience people say about that, if we reach a conclusion that it's ok, then no problem for me.But in all case I think you should tell the factory about this problem, just in case.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: November 08, 2016, 10:07:20 pm
content: Especially if they send a second batch of good boards out. Then you can pick and choose...How do the boards look with a gerber viewing tool?

author: VK5RC
author_rank: Unknown
timestamp: November 08, 2016, 10:32:26 pm
content: I would be happy to pay for 3 of those boards, others may want a re-spin.My level of volt-nuttery (if you know what I mean) isn't too high.

author: HighVoltage
author_rank: Super Contributor
timestamp: November 08, 2016, 11:04:35 pm
content: I do not have enough experience with LTZ1000 PCB's to judge if this is a real problem or not.

author: mimmus78
author_rank: Unknown
timestamp: November 08, 2016, 11:10:16 pm
content: They have integrated GERBER PRE-VIEW, and was all OK.You can carefully remove the solder mask by scraping and than eventually add some solder on one point, but these "broken" ring guard around LTZ1000 I don't know.I think we are going to populate this board with 200/300 USD worth of components, and make a huge investment in time and money to characterise it.I don't like the idea of having some unknown because someone decided to change PCB design.I just wrote to the fab (I spotted also other solder mask not removed), let see what they say.

author: plesa
author_rank: Frequent Contributor
timestamp: November 08, 2016, 11:30:11 pm
content: I suppose that open guard is not big difference if any. The majority of trace is still guarded.Similar to solder mask covering guard trace. If someone is curios about difference you can measure it by electrometer.Of course you can ask for some discount on PCB.

author: klaus11
author_rank: Unknown
timestamp: November 09, 2016, 09:14:13 am
content: Because of my absolute lack of knowledge, development and manufacture of PCBs, I have no idea what he is talking about.What the majority decides will also be good for me.

author: mimmus78
author_rank: Unknown
timestamp: November 09, 2016, 10:20:51 am
content: So I submitted the original project from xdevs.com and those pcb where fabricated at EasyedaI checked the gerber files with their online tool before submitting project and it was shown like the attached image.At fist sight seemed OK to me including ring guard, but it's clearly not now, I should have checked better!The problem is that on this part of the pcb the "solder mask" mask layer is not aligned with the trace.They removed the solder mask, but there is no trace down. Il will check with TiN this point as the problem is likely in the files I downloaded from xdevs.com.Anyway, as told you can still scrub this piece to get exposed guard.As for the other problem I'm convinced too what plesa said: "I suppose that open guard is not big difference if any. The majority of trace is still guarded.".So at this point, who still wants the PCB please send me by PM the address and if they prefer "registered mail" or "standard mail".I will get quote for shipping and back to you with costs.

author: mimmus78
author_rank: Unknown
timestamp: November 09, 2016, 10:34:33 am
content: Updates on prices:I spent 176 EUR total instead of preventivated 160. DHL charged me other 12 EUR for the customs declaration paperwork.Anyway because I got 22 boards instead of 20, price will remain the same 8 EUR.

author: klaus11
author_rank: Unknown
timestamp: November 09, 2016, 11:02:55 am
content: Mimmus, I'll stay with my two boards, if you have a post on how to correct the problem, why I still do not understand where the problem is due to my ignorance of English language comprehension

author: mimmus78
author_rank: Unknown
timestamp: November 09, 2016, 11:41:23 am
content: Packaging:- VK5RC 3pcs - Paid - Registered- HighVoltage 2pcs - Paid - Registered - overbooking list- Mimmus78 3pcs - that's meConfirmed waiting for payment:- klaus11 2pcs - Spain zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- t2kv 2pcs - Australia zone 3 - priority mail 5.50 EUR - registered 9.95 EUR- Nuno_pt 3pcs - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- msliva 3pcs - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list=======================TOTAL 22 pcsREMAINING 0 pcsWaiting or confirmation- pelule 3pcs - please confirm and send me address for shipment quotation=======================TOTAL 3pcsTOTAL CONFIRMED + UNCONFIRMED = 25

author: HighVoltage
author_rank: Super Contributor
timestamp: November 09, 2016, 12:05:46 pm
content: I am also stay to word and take 2 boardsPM sent

author: mimmus78
author_rank: Unknown
timestamp: November 10, 2016, 09:33:00 am
content: I updated previous post with shipment costs.A PM message with my PayPal address will be sent to everybody that sent me the complete address and get the shipment quotation.Who is in overbooking please wait a couple of days, I'm still waiting a response from 4 members.

author: HighVoltage
author_rank: Super Contributor
timestamp: November 10, 2016, 10:48:09 am
content: Paypal sent

author: fanOfeeDIY
author_rank: Unknown
timestamp: November 10, 2016, 11:09:24 am
content: Quote from: mimmus78 on November 10, 2016, 09:33:00 amThank you for making the pcbs.I may be in the overbooking list, I just replied to your PM.

author: klaus11
author_rank: Unknown
timestamp: November 10, 2016, 03:46:34 pm
content: I have not received PM message

author: mimmus78
author_rank: Unknown
timestamp: November 10, 2016, 08:18:11 pm
content: Quote from: klaus11 on November 10, 2016, 03:46:34 pmPM sent

author: mimmus78
author_rank: Unknown
timestamp: November 10, 2016, 08:26:38 pm
content: Packaging:- VK5RC 3pcs - PM SENT - Paid - Registered- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- Mimmus78 3pcs - that's meConfirmed waiting for payment:- klaus11 2pcs - PM SENT - Spain zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- t2kv 2pcs - PM SENT - Australia zone 3 - priority mail 5.50 EUR - registered 9.95 EUR- Nuno_pt 3pcs - PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- msliva 3pcs - PM SENT - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list=======================TOTAL 22 pcsREMAINING 0 pcsWaiting or confirmation- pelule 3pcs - please confirm and send me address for shipment quotation=======================TOTAL 3pcsTOTAL CONFIRMED + UNCONFIRMED = 25

author: TiN
author_rank: Super Contributor
timestamp: November 11, 2016, 04:49:04 am
content: Sorry folks, I couldn't post before due tothis cookery, but now I'm with you allFirst hats off tomimmus78, this was unexpected joy to see someone actually going to order my volt-nut designThe issues with soldermask opening is from my gerber file, I forgot to update the file B01. My own boards were corrected B02-version.However those will not affect anything in measurable way, so it's still alright to use. If it bothers you, soldermask can be carefully scrapped off, but I'd leave it as is.Other thing is manufacturing tolerance specs. I obviously did not expect someone to order the PCBs on usual hobby-level run fabs, so Gerbers are at 4mil/4mil spec. It does not have to be that precise, so I'll update it to be more friendly and replace GERBER on the article.As of resistors, I would try to have best stability/tempco resistors for 1K/13K and 120 ohm ones, as these are key for LTZ1000 operation temperature and current. 70K can be less fancy and cheaper, and even vary in value 65-80K. You can see on HP 3458A A9 ref board there are just usual metal-films, and that board is totally fine to get <0.05ppm/K tempco, I tested it.Opamps I use on my modules are controversial LTC2057 and now ADA4522-1 on this latest module covered in this thread before. No issues discovered.Module can work with any input voltage from 10V to ~20V without problems and should not show dependence from input voltage. Regular LDO like 7815 with few decoupling caps will do job fine. Avoid switching PSUs though. There is no polarity protection on board, so double check connections and wiring before turning power on!Normal current consumption with 1K/13K heater setting is ~28-32mADC steady state. It warms up to operation spec within 5-10 minutes.Be careful with output too, it's not protected and directly connects to zener in LTZ1000A. If you short it or inject current into zener you are likely to cause stress/permanent damage the chip.

author: klaus11
author_rank: Unknown
timestamp: November 11, 2016, 07:09:02 am
content: Paypal sent

author: mimmus78
author_rank: Unknown
timestamp: November 11, 2016, 10:48:15 am
content: Packaging:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- Mimmus78 3pcs - that's meConfirmed waiting for payment:- Nuno_pt 3pcs - PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- msliva 3pcs - PM SENT - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list=======================TOTAL 22 pcsREMAINING 0 pcsWaiting or confirmation- pelule 3pcs - please confirm and send me address for shipment quotation=======================TOTAL 3pcsTOTAL CONFIRMED + UNCONFIRMED = 25

author: pelule
author_rank: Frequent Contributor
timestamp: November 11, 2016, 04:13:04 pm
content: PM sent, still in for the 3 pcs.

author: mimmus78
author_rank: Unknown
timestamp: November 11, 2016, 11:43:01 pm
content: Hi guys I have good news.The PCB are going to be fabricated again ... they decided to be very nice, redo and ship the lot as soon as possible.As consequence of this I think we have enough PCB for everybodyI think they are going just to correct the open guard track as they didn't asked me to send new gerbers.I still don't have idea when we will get the new PCBs and if I will need to pay customs and VAT again.What do we want to do?

author: mimmus78
author_rank: Unknown
timestamp: November 11, 2016, 11:49:43 pm
content: Packaging:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- pelule 3pcs - PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- Mimmus78 3pcs - that's meConfirmed waiting for payment:- Nuno_pt 3pcs - PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- msliva 3pcs - PM SENT - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait I receive second lot):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list- little 2pcs. - Germany overbooking list=============================TOTAL 22 pcswait list (overbooking) 3 pcs

author: plesa
author_rank: Frequent Contributor
timestamp: November 12, 2016, 12:10:45 am
content: Quote from: mimmus78 on November 11, 2016, 11:43:01 pmDid you already ordered resistors? They have extra long leadtime or you are going to use some thin film like PTF56/UXB series?Good choice can be Rhopoint ( they will fit to TiN boards )https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 12:33:30 am
content: I contacted Edwin and Vishay. Finished to order some resistor from Edwin. I really don't even checked if this resistors will fit, but I'm also going to build my PCB version so for sure I will use it.Still waiting for Vishay response, I really liked the idea to have this first board I build with Vishay. I asked fancy pants VHP101 for the heater divider a some other normal in plastic for the others 3.The main problem I have is that I still don't have 3458A ... I'd like to try to buy same old rusty broken one if it will pop out somewhere, but you must be brave to do this extreme repairs like TiN.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: TiN
author_rank: Super Contributor
timestamp: November 12, 2016, 07:26:16 am
content: QuoteNo bravery needed, just have 2-3K$ cash handy and you will do fine. If A3 ADC bad - 1400$ for replacement. Repeat until it's stable. It's no different than any other electronics repair, other than requirement of stable and verified calibration sources for DCV and OHM. For the first one you already on the correct way with LTZ module (you can calibrate 3458A to other calibrated 3458A using 7V LTZ output. I even had luck totransfer DCV internationally using A9 LTZ module, and got only 6ppm of error in the end.I'm looking forward to see all you guys build some units and get them tested. I did not expect this thread to go this way,.As special case I'd be happy to offer calibration for your finished builds after it's all working and burned-in first 200 hours. Rules would be simple:1. Build your KX-module, publish short worklog in this thread (few photos of assembled PCBA, photo of it running with DMM hooked up showing 7V)2. Leave it running for 200 hours, so initial drifts get stabilized. Module should be enclosed in some box without vents.3. Measure it again, record the temperature and voltage and put a label with values on the box4. Ship the box to me (Taiwan). You pay shipping.5. I'll power your box with +15V for 48 hours to have everything stabilize6. Test 7V output voltage in temperature span +20....+30C, record the graph7. Unit will be shipped back via EMS Express (~30-40$USD, 4-7 days to USA, bit more to EU). You pay shipping.I don't have official Keysight/Tektronix/etc calibration certificates for my 3458A, but I'm confident it's +/-2ppm (likely <1ppm) on DCV.All steps are required

author: VK5RC
author_rank: Unknown
timestamp: November 12, 2016, 08:48:08 am
content: I would like to thank both TiN, for putting his hard work designs up for open review/reproduction and Mimmus78 for putting in the pcb gerbers etc and doing all the postage / customs etc.TiN, if that offer re calibration check is open in a month or so, it will be hard to refuse!Robert

author: TiN
author_rank: Super Contributor
timestamp: November 12, 2016, 08:50:30 am
content: Let's make it so: offer valid for any KX reference board once, without time limitation, unless my homelab get major change, which isn't planned.

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 09:51:04 am
content: TiN this offer of free calibration will be interesting but we should find a way to ship back and forth without paying customs.I should check how this can be done.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: plesa
author_rank: Frequent Contributor
timestamp: November 12, 2016, 10:53:57 am
content: I can offer you similar service like TiN in Europe.1. Measure it with calibrated 3458A/002 in reasonable temperature range.2 . For extreme voltnut - close to me is JJA and they can measure it for 400 EUR / 2-3 weeks of monitoring.What I will add is power cycling for few days ( On for 1h and off or 30min to cool down).And maybe bake the LTZ1000 prior assembly.For shipment can be handy to monitor temperture if you are going to ship it in winter time.

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 01:17:05 pm
content: Plesa that's very nice for all European guys to have this opportunity.O men you have JJA near home! I cannot even comment it.Anyway regards Edwin resistors, despite last problems with quality in last year I think it is the best and cost effective way to get reasonably TC matched resistors for the heater.Keep this ratio constant is 10 times more important that all other factors.I read somewhere that resistors made by same person, one after the other can have similar drift and TC.You can ask Vishay for this, but I this it will increase even more the costs. So I just asked Erwin for this and this seems to be the most practical and cheap way to get this point.Hope he really solved issues with his epoxy in meantime.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2016, 01:32:20 pm
content: Quote from: plesa on November 12, 2016, 10:53:57 amI can do a similar service in the UK, if somebody needs it, as the HP3458A Opt 002 just came back from calibration at Keysight. I don't have a temperature chamber yet (though it may change soon), however I can monitor the lab temperature (or the reference enclosure temperature).CheersAlex

author: TiN
author_rank: Super Contributor
timestamp: November 12, 2016, 01:39:00 pm
content: plesa, Alex NikitinIf you OK, I can add this section into article on my site, with links to your profile, to keep this program afloat?

author: plesa
author_rank: Frequent Contributor
timestamp: November 12, 2016, 01:54:12 pm
content: Quote from: TiN on November 12, 2016, 01:39:00 pmOf course.

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 02:04:59 pm
content: Fist shipment is ready ... I'm still waiting payment from other 4 members. Let me know if someone have any problem.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 02:07:22 pm
content: OK I think we just need one 3458a for Italy now. I should ask my wife ...Inviato dal mio Nexus 6P utilizzando Tapatalk

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2016, 02:36:41 pm
content: Quote from: TiN on November 12, 2016, 01:39:00 pmYes, sure.CheersAlex

author: TiN
author_rank: Super Contributor
timestamp: November 12, 2016, 03:50:22 pm
content: Added a section about calibration offeron siteAlso updated top post in thread. Thanks!Calibration byAccuracy / StandardRegion/Country Contact for participantsxDevs.com<2ppm / 3458A-mod + 2*K2002Asia/TaiwanEEVBlog forum PMplesa<4ppm / 3458A-002Europe/SwedenEEVBlog forum PMAlex Nikitin<4ppm / 3458A-002Europe/UKEEVBlog forum PM

author: HighVoltage
author_rank: Super Contributor
timestamp: November 12, 2016, 04:46:36 pm
content: I am still in the middle of getting to know my 3458A (8 ppm) and will have it officially Keysight calibrated in a few month time. If anyone needs its KX reference board measured in Germany, you can send it to me, as long as you pay shipping. I can also offer a comparison to my 34470A and DMM7510.But, until now I can not change the temperature, that is a future project.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 12, 2016, 05:48:20 pm
content: Probably plenty of 3458As in the US, but I'm happy to offer comparisons with an in Cal DMM7510 and K2010.I also have an 0.05% Hameg 8118 LCR.

author: mimmus78
author_rank: Unknown
timestamp: November 12, 2016, 10:19:37 pm
content: This is going to be huge ... a global volt nut club.Thanks to plesa I asked to rhopointcomponents.com too for a quote of the resistors. I will let you know what happens.

author: mimmus78
author_rank: Unknown
timestamp: November 14, 2016, 08:56:10 am
content: UPDATES:Hi guys, I shipped the 5 packages to VK5RC, t2kv, klaus11, HighVoltage, pelule.For all that paid for registered main I will send them a PM with the tracking number.I'm still waiting payment by: Nuno_pt, msliva. I sent them 2 PM but they seems kinda busy now.I have other 8 spare PCBs, I think if I don't get notice from them I a couple of days I will start accept payment from to the "overbooking list".Shipped:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- pelule 3pcs - PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- Mimmus78 3pcs - that's meConfirmed waiting for payment:- Nuno_pt 3pcs - PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- msliva 3pcs - PM SENT - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait I receive second lot):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list- little 2pcs. - Germany overbooking list=============================TOTAL 22 pcswait list (overbooking) 3 pcs

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 14, 2016, 09:15:28 am
content: Quote from: Alex Nikitin on November 12, 2016, 01:32:20 pmPlesa, Alex, and also HighVoltage:What kind of KS calibration and report for your 3458As did /will you get?The single page report, which only confirms that the instrument is in 1 years specification limits, or the elaborate, much more expensive, multi page calibration report, with all measurement results (as found) including test limits?I think, if it's only the first kind, it won't be sufficient for this purpose, as the 1 year DCV specification is 8ppm / 4ppm for option 002 only, and about <= 1ppm uncertainty is required.Frank

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 14, 2016, 10:54:42 am
content: Quote from: Dr. Frank on November 14, 2016, 09:15:28 amHi Frank,Here is a page from the certificate. I hope it answers your question.CheersAlex

author: HighVoltage
author_rank: Super Contributor
timestamp: November 14, 2016, 10:59:08 am
content: Dr.Frank,My plan is to have my 3458A adjusted and calibrated to the higher specs and I want the multi page calibration report. But I have not even started to talk to KS. May be I will visit KS Boeblingen first to see their capabilities and then make my mind up. On the other side, I can also have it calibrated in Hamburg against a calibrated 732A. But first I will have the instrument running for a few more month to get it stable.

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 14, 2016, 11:35:32 am
content: Quote from: Alex Nikitin on November 14, 2016, 10:54:42 amAlex, definitely.. your 10VDC uncertainty will be around 3ppm, probably better, as the 10Vdc reading of your instrument is given to < 1ppm resolution, and the "Golden 3458A", which defined the limits, may have been less uncertain than 1ppm.For sure, this calibration did cost a fortune.Frank

author: plesa
author_rank: Frequent Contributor
timestamp: November 14, 2016, 05:26:53 pm
content: Quote from: Dr. Frank on November 14, 2016, 11:35:32 amI have same uncertainties like Alex, because we are sharing calibration lab

author: mimmus78
author_rank: Unknown
timestamp: November 14, 2016, 07:52:02 pm
content: At the end I ordered 2 more sets of resistors (the one DR. Frank used) ... unfortunately there was no stock of 1K value up to the end of this month. So it's still waiting time ...I'll build a couple of pieces with TiN PCB and use this as reference. After this I will build a couple with my "new" design.In this new design, I'd like to experiment a little new gimmick with a "new" schematics that is my interpretation of years of post of the old LTZ1000 thread.It will be not an extreme design, just take the best ideas of the old thread and put all together (some Andreas's noise reduction caps, Solartron's caps on the heater and the new op-amp TiN used in his last build, but I still have to decide final op-amp).I'd like to add also a buffer for the 7V output to prevent problems with shorting the zener. Maybe also revive the 7.X to 7 and 7 to 10 ratio scaling used by Dr. Frank.Hope I have time and skills to complete the design with some good result (I have not such experience with analogue stuff).Inviato dal mio Nexus 6P utilizzando Tapatalk

author: Zucca
author_rank: Unknown
timestamp: November 15, 2016, 10:17:16 am
content: mimmus78please consider to do more boards when you are ready. I would like to buy one... may I?

author: TiN
author_rank: Super Contributor
timestamp: November 15, 2016, 10:41:37 am
content: Zucca, where is the one assembled one you have already?

author: mimmus78
author_rank: Unknown
timestamp: November 15, 2016, 11:06:15 am
content: Quote from: zucca on November 15, 2016, 10:17:16 amAdded you to overbooking list.I still have 8 spare from some users here they didn't confirmed, I will wait up to the end of the day and than offer to the one that are on queue on the overbooking list ... anyway another lot is going to be fabricated.D.UPDATED:Packaging and shipping on Friday:- Nuno_pt 3pcs - PM SENT - Portugal zone 1 - priority mail 3.50 EUR - registered 7.90 EURShipped:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- pelule 3pcs - PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- Mimmus78 3pcs - that's meConfirmed waiting for payment:- msliva 3pcs - PM SENT - Czech Republic - zone 1 - priority mail 3.50 EUR - registered 7.90 EURConfirmed but in overbooking list (do not pay - wait I receive second lot):- SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list- fanOfeeDIY 2pcs - Japan - priority mail 5.50 EUR - registered 9.95 EUR - overbooking list- kutte 2pcs. - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR - overbooking list=============================TOTAL 22 pcswait list (overbooking) 4 pcs

author: Zucca
author_rank: Unknown
timestamp: November 15, 2016, 10:32:22 pm
content: Thxmimmusjust one thing I am in Germany not in Italy... ma sono italiano...TiN... the one I have is just ready for testing my K2001. Later I plant to put it in the K2001 ADC replacing the VR801 6.4 V Zener...just curious to see what will happen

author: Zucca
author_rank: Unknown
timestamp: November 16, 2016, 08:17:13 am
content: Ohh I got a PM from Mimmus confirming that the boards in discussion is the TiN one... but I meant the Mimmus new design one, which is not ready yet. Soo please take me out from the list and put me in he new one of your design.ThanksTiNagain for sending me his wonderful KX LTZ1000A board.

author: mimmus78
author_rank: Unknown
timestamp: November 16, 2016, 10:15:28 am
content: @zucca no problem ... I'll keep you posted if I manage to finish my design in next weeks.@Nuno_pt I will ship your package on Friday.As in not hearing from msliva in days I will send PM for payment instruction also to the overbooking list ...

author: mimmus78
author_rank: Unknown
timestamp: November 16, 2016, 03:47:50 pm
content: I don't understand why use VR801 as integrator reference? Any reason why not route LM399 ref signal there?

author: SvanGool
author_rank: Regular Contributor
timestamp: November 16, 2016, 03:50:24 pm
content: @mimmus78, as you requested to report on the forum:I sent you the money for: - SvanGool 2pcs - Netherlands zone 1 - priority mail 3.50 EUR - overbooking listThanks !

author: mimmus78
author_rank: Unknown
timestamp: November 16, 2016, 04:07:46 pm
content: 3 more PCB to go.

author: kutte
author_rank: Contributor
timestamp: November 16, 2016, 04:20:38 pm
content: 20,00 Euro for 2 boards via priority mail sent from kutte

author: mimmus78
author_rank: Unknown
timestamp: November 16, 2016, 08:01:45 pm
content: Thanks Guys, PCB are over.I didn't hear from the fab for the "fixed" batch, I will let you know when then new batch will arrive.Anyway let me know if someone else is interested.

author: dr.diesel
author_rank: Super Contributor
timestamp: November 16, 2016, 08:08:58 pm
content: Quote from: mimmus78 on November 16, 2016, 08:01:45 pmIf you end up ordering another batch, I'll take 5 to the USA.

author: fanOfeeDIY
author_rank: Unknown
timestamp: November 17, 2016, 09:21:03 am
content: Hi mimmus78,Thank you for your message. I am in the overbooking list.I missed reading it last night, but it is fine. I will wait for the next batch.

author: mimmus78
author_rank: Unknown
timestamp: November 17, 2016, 10:06:23 am
content: UPDATED:Packaging and shipping on Friday:Shipped 18/11/2016:- Nuno_pt 3pcs - PM SENT - Paid - Priority- SvanGool 2pcs - PM SENT - Paid - Priority- kutte 2pcs - PM SENT - Paid - PriorityShipped 11/11/2016:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- pelule 3pcs - PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- Mimmus78 3pcs - that's meConfirmed:- msliva 3pcs - PM SENT- fanOfeeDIY 2pcs - PM SENT- dr.diesel 5pcs - PM SENT- z01z 3pcs - PM SENT

author: mimmus78
author_rank: Unknown
timestamp: November 17, 2016, 10:18:38 am
content: So this is what I elaborated. This is based mainly on last revision of battery powered reference from "andreas".I added reverse polarity power protection.Removed some caps that Dr. Frank defined as "fear" caps.I removed the MOS that drive current to the zener.Using LTZ1000 (not A version)I was thinking to add some basic output protection to the REF ... what you think to add something like this (with opportune op-amp):just after the buffered output of the LTZ1000A?As usual care to thermal EMF is a must. Hope it will not upset much the output.

author: Zucca
author_rank: Unknown
timestamp: November 17, 2016, 10:59:16 am
content: Mimmus can you put some 0R jumpers or somenthing to separate the heater power supply path from the rest? SeeTiNarticlehere:Quote

author: Zucca
author_rank: Unknown
timestamp: November 17, 2016, 11:14:44 am
content: Quote from: mimmus78 on November 16, 2016, 03:47:50 pm+1 I really don´t know why...

author: mimmus78
author_rank: Unknown
timestamp: November 17, 2016, 12:55:45 pm
content: Quote from: zucca on November 17, 2016, 10:59:16 amI added R10 just before the heater transistor, this can be 0R or used also to split VCC.I don't know if is good to add also on the GND side.

author: mimmus78
author_rank: Unknown
timestamp: November 17, 2016, 01:17:01 pm
content: Hi guys, I got called from DHL because there is a new parcel for me (and I wasn't home) ... so guess what it will be?I will let you know when back in home if it's some gift from unknown or if it's the new KX pcb batch.

author: mimmus78
author_rank: Unknown
timestamp: November 17, 2016, 07:40:11 pm
content: New pcb lot arrived. This new lot has no missing part on the guard ring around LTZ1000.I will ship this new lot in parcels shipping tomorrow, and it seems we will have enough pieces also for how was in the overbooking list.If someone that get the old PCB cannot sleep with the mistaken one I can ship the new corrected PCB for free (you just pay postage). This offer is valid just for few days.I will send pm later to the ones that where in overbooking list.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: Andreas
author_rank: Super Contributor
timestamp: November 17, 2016, 07:49:23 pm
content: Quote from: mimmus78 on November 17, 2016, 10:18:38 amHello,are you shure that C10 is on the "right" side of the resistors?With best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2016, 08:46:08 pm
content: Using chopper OPs for the LTZ1000 circuit can get tricky. They produce quite some RF spikes can have higher noise in kHz range, where the transistor in the LTZ is not helping anymore. There is no real need to replace the LT1013 or similar OP. The LT1013 is not that expensive. But at least dual OPs use the same pinout.For the extra butter, the AZ OP is suitable, as here the error from the OP fully enters.One might think about having some RC filtering here - to reduce higher frequency noise from the reference and keep spikes from the AZ OP away from the reference.With a relatively high current, there was a good reason to have a transistor / JFET to drive the reference current. If one really wants to save on this, one could still use a bridge or diode like shown, but I would really have the space for the transistor on the board.

author: Andreas
author_rank: Super Contributor
timestamp: November 17, 2016, 09:16:21 pm
content: Hello,Quote from: Kleinstein on November 17, 2016, 08:46:08 pmDo you have founded measurement values on this?I have not measured any differerence between LT1013 and LTC2057 on my latest 4 references.Quote from: Kleinstein on November 17, 2016, 08:46:08 pm+1I fully agree I measured large differences between filtered and unfiltered buffer regarding EMI sensitivity.Quote from: Kleinstein on November 17, 2016, 08:46:08 pmThe main intention of the FET-Buffer was LT1013-related together with reduced power supply voltage.keep heating away from LT1013 with relative high offset drift+ extend output voltage range of the LT1013 (level shift) for reduced battery voltage.So with a rail to rail chopper I see no reason to use a (now obsolete) FET.The initial design is now already 6 years old.With best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: November 18, 2016, 12:30:43 am
content: Quote from: Andreas on November 17, 2016, 07:49:23 pmWell yes, better to move it before. The idea is to have a low pass filter to reduce the noise, and maybe also EMI. Don't know how and if it will works.I added also some load on the buffered output ... what I have to check on datasheet to confirm 47K is sufficient (maybePeak to Peak Current Noise)?I added also limit to output swing of the protection circuit ... this will protect from almost any negative or something like > 11V + couple diode drop.Do not expect any CAT rating here, it may be not sufficient to save the last opamp but at lest rest of reference should be safe if some low voltage is applied to the binding posts by error.Anyone have a good example of 10V reference protection? Don't know how much this will upset the result.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 18, 2016, 08:50:32 am
content: The "filter" around R15,R16 C10 is there to make the buffer amplifier tolerant to capacitive load.I don't really understand the protection circuit shown at the output - to me this makes little sense. If needed at all I would more expect kind of a beefy 8 V zener diode or equivalent circuit.One point where an extra protection might make some sense would be the unbuffered output. This is known to be sensitive to a short or overload (e.g. large uncharged capacitor), as this would cause the heater to activate all the way. A protection could check for a drop of the output by more than an few millivolts and in this case turn down the heater. It could take as little as a tl431 and a few resistors and a diode.

author: Andreas
author_rank: Super Contributor
timestamp: November 18, 2016, 10:48:11 am
content: Hello,that´s what I have planned for my Rev "C" board.C23 EMI filtering.R25 C24 (wideband) noise filtering and limiting back current to LTZ1000 zener via the OP-Amp input protection diodes in case of output shortening.(I am still looking for good ideas for a temperature stable 7 to 10V transfer)with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: November 18, 2016, 11:57:01 am
content: UPDATED 2016 Nov 25 - 22:30 Italy timeWe still have: 8 PCBs with 1mm guard missingWaiting for payment:- msliva 3pcs- bingo60 2pcs=========================================================Shipped 25/11/2016:- z01z 3pcs (new pcb)- SvanGool 2pcs (new pcb)- fanOfeeDIY 2pcs (new pcb)- villas 2pcs (new pcb)=========================================================Shipped 18/11/2016:- Nuno_pt 3pcs - PM SENT - Paid - Priority- SvanGool 2pcs - PM SENT - Paid - Priority- kutte 2pcs - PM SENT - Paid - Priority- dr.diesel 5pcs - PM SENT - Paid - Registered=========================================================Shipped 11/11/2016:- VK5RC 3pcs - PM SENT - Paid - Registered- t2kv 2pcs - PM SENT - Paid - Registered- klaus11 2pcs - PM SENT - Paid - Priority- HighVoltage 2pcs - PM SENT - Paid - Registered - overbooking list- pelule 3pcs - PM SENT - Germany zone 1 - priority mail 3.50 EUR - registered 7.90 EUR- Mimmus78 3pcs - that's me=========================================================

author: mimmus78
author_rank: Unknown
timestamp: November 18, 2016, 12:03:55 pm
content: Quote from: Kleinstein on November 18, 2016, 08:50:32 amYes I rushed a little bit the design, and this is ok for just ~ 0.6V. Considering sense is attached to the binding posts maybe just some zeners is enough.Quote from: Kleinstein on November 18, 2016, 08:50:32 amI don't plan to expose this network outside the reference ... maybe this ca be still useful if some op-amp will die. I will check it.How to calculate what minimum load I need to present to the op-amp?

author: villas
author_rank: Newbie
timestamp: November 18, 2016, 05:14:42 pm
content: I would like to build one reference, but I probably will not be able to find the resistors here and I don't like the idea getting these from eBay.Do you guys plan to group buy the low TC resistors from VPG or some distributor?

author: mimmus78
author_rank: Unknown
timestamp: November 18, 2016, 07:43:41 pm
content: Flintstone: this R is used for temperature compensation in LTZ1000A and is not necessary in not A version.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: d-smes
author_rank: Regular Contributor
timestamp: November 18, 2016, 08:12:09 pm
content: Quote from: mimmus78 on November 18, 2016, 07:43:41 pmIt's the other way around per data sheet- don't use resistor for "A" version.

author: mimmus78
author_rank: Unknown
timestamp: November 18, 2016, 08:22:18 pm
content: Ohh guys I was 100% sure was the other way around ...

author: Andreas
author_rank: Super Contributor
timestamp: November 18, 2016, 09:13:59 pm
content: Hello,I use R9 also for the A version to fine adjust the T.C.But not always 400K is the right value:https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=253898with best regardsAndreas

author: bingo600
author_rank: Super Contributor
timestamp: November 18, 2016, 10:03:48 pm
content: @mimmus78I'd like to get 2 boards from the "overbooking list" if possible/Bingo

author: dr.diesel
author_rank: Super Contributor
timestamp: November 18, 2016, 10:52:30 pm
content: Quote from: plesa on November 12, 2016, 12:10:45 amWow, they stock a big range of 3PPM parts! I don't have any experience with these guys unfortunately, might be a good alternative depending on how busy Edwin's shop is.

author: mimmus78
author_rank: Unknown
timestamp: November 19, 2016, 12:38:29 am
content: Here are options I found:Vishay VHP101VHP101 is the most stable and expansive resistors you can get (few PPM for years or °C) ...if you have big pocket and a very special LTZ1000 you can use this two for the heater divider.UsingVHP101also for the other resistors to me is just a waste of money.If you like Vishay nameS102CandZ202are good too, and they can be used forthe other resistors at half the price of the VHP101.TE Connectivity UPW50UPW50 has TC 3PPMx°C and 25PPM x year stability.You can buy at rs components or other store at 7 to 10 EUR each one.Not all values are directly available, so you must buy multiple items to form the 70K and the 12K resistors.I brought two sets and I spent less than 150 EUR for both @ rs components. You can find this on findchips.ECONISTOR 8G16D @ rhopointcomponentsVery similar specs and price to UPW50 but you can request for custom values of "70K" and "12K" values.They have higher EMF from UPW50. I get a quotation as low as 50 EUR per set. Cannot find this on findchips.EDWINIt's the cheapest of all others, specs are similar to the others (UPW50, ECONISTOR) but you have few weeks of lead time.He had some problems in past with this resistors. I ordered 3 sets from him too, let's see when they arrive.

author: SvanGool
author_rank: Regular Contributor
timestamp: November 19, 2016, 12:06:38 pm
content: Quote from: villas on November 18, 2016, 05:14:42 pmFor the last days, I was in contact with Edwin (the resistor expert) about the resistors for this project, although most answers can be found in the several LTZ1000 threads, I found them very useful, a little summary (with permission of Edwin):Q : People advise me to use 12k5 or 13k iso 12k for the heater in case of a LTZ1000A (which I have), can you advise?A1: In the case of the LTZ circuits, using resistors such as the Vishay Z202 and VHP203 will not get you any noticeable improvement in the Vref's performance. That circuit is quite insensitive to low resistor TCR and low long term drifting. Where the resistor performance becomes much more important is in the circuit that raises the LTZ voltage to about 10V at the output. The best performance of the LTZ is achieved with the Linear Tech circuit as given in the data and app notes.A2: The LTZ1000 (non-A) does allow for a slightly lower overhead temperature internally, about 5°C above the highest environmental temperature expected in operation, whatever the source may be, internal instrument temperature may be higher than room temperature. Use of 12K, 12.5K, or 13K with the 1000 is often acceptable. What you don’t want is for the LTZ to run out of compensation room for temperature because it will no longer be able to compensate for temperature and you will see a significant change in output voltage.A3: For the LTZ1000A version, it requires at least 10°C overhead in temperature, this usually required at least 13K or higher. According to LT, beginning about two years ago, the new production of the ‘A” version was recommended to use a 15K resistor period, this is the value (HP, Agilent,) Keysight, and Fluke are using in their units (the 3458A, ECT.). If I was building an LTZ module I would use the 15K as recommended.Q : Do these heater divider resistors need to be thermally coupled (tracking TC), how would I do that?A : The heater divider resistors is a bit sticky, if you encapsulate the module in say foam and not just a ‘box’, the resistors will achieve equilibrium without any special effort. If the module is not encapsulated, then wrapping a layer of copper tape around the two resistors will make a significant difference in tracking. You must remember that whatever the case is, it is going to take some time for everything to warm up and equalize, until then you will see a higher than ‘normal’ drift. If after about 30-60 minutes you are still seeing some wobble, you have an air draft problem most likely.Q: What is the best way to mount these type 802 resistors in TiNs 0,125" and 0,150" PCB sockets and can I use normal SnPb solder?A : The dimensions of the 802 is 0.250” D x 0.375” L (6.35mm x 9.53mm) with 22 AWG leads, leaded solder is just fine.Q : Do I have to take some special precautions to protect your resistors against humidity?A : No, the resistors are not humidity sensitive to any significant degree.Q : What would be the cost and lead time for your resistors and could a group discount be applicable?A: For 1-9 pieces, a group buy would lower these prices and reduce shipping cost (1st Class International is $13.50, International Priority is $33.95 for Europe):1x 120R0, ±0.1%, type 802 $6.851x 1K, ±0.1%, type 802 $6.341x 12K or 15K, ±0.1%, type 802 $7.352x 70K, ±0.1%, type 802 $8.64Current ship dates are approximately 4-5 weeks, perhaps a little less depending on circumstances.

author: mimmus78
author_rank: Unknown
timestamp: November 20, 2016, 07:20:15 pm
content: UPDATE 25/nov/2016 22:30 Italy time:All PCB in new batch are already sold but if you accept the one with this small defect I still have someone unsold that I'm not going to use.If you want it just send me a PM.Updated pcb shipping status -->HERE

author: mimmus78
author_rank: Unknown
timestamp: November 25, 2016, 09:54:00 pm
content: RS components today shipped me the last two precision resistor I was missing for starting build this KX reference.Is there any easy and effective way to check TC of the resistors without having a thermal chamber?

author: Andreas
author_rank: Super Contributor
timestamp: November 25, 2016, 10:30:38 pm
content: Hello,I do it with a peltier (car) cooling box + heater foils on a heat spreader for a ~30 deg C temperature range:https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462298/#msg462298Frank uses a freezer cooling pad in a isolated box.https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg466319/#msg466319If you want repeatable measurements you should keep the wires of the resistor at the same temperature.I use aluminium stripes + silicone padsWith best regardsAndreas

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 25, 2016, 11:02:08 pm
content: Well, I'm using a dynamic temperature change method, so the measurement are always done during ramping up/down of the temperature.If that change is slow enough, nearly everything is in equilibrium, and the measurement will be precise enough.My final setup is here:https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg617211/#msg617211The aluminium block, which carries the resistor and the thermometer are additionally mounted inside an outer aluminium box so that also all the wires are on the the same temperature as the alu block and the outer case (thermal short circuit), This is essential, as most of heat transfer happens via the resistors wires.I only have difficulties to observe very slow events correctly, like the described hysteresis and creeping effects on some of the econistor resistors.It would be very useful to let the resistors relax on a constant temperature after a change for many hours.I'd expect that the formerly hysteretical resistors would have a much lower T.C. than being falsified by the hysteresis effects.General Resistors told me, that they let their DUTs rest for 24h on the edge temperatures, and they had totally different results than me on the same specimen.In that sense, Andreas solution is much more versatile, and the temperature can be controlled in a much better manner, and the whole temperature profile (T-loop) can be achieved automatically.B.t.w., I will soon publish T.C. adjustment experiments on my new LTZ#5 reference, where these hysteresis effects, supposedly caused by exactly these resistors, are strongly dependent on the temperature change rate, and so does the evident T.C.For a quick selection and characterization of the PWW resistors and the LTZ circuit itself, my dynamic measurement approach was completely sufficient.. the LTZ reference after a few attempts, now has nearly zero T.C.Frank

author: mimmus78
author_rank: Unknown
timestamp: December 06, 2016, 02:53:01 pm
content: Something pop out todays ... unfortunately I'm still dealing with resistors TC characterisation where I found something strange (to me) and I hope I can publish some results in a few days.It's not the time to build the KX yet ...

author: TiN
author_rank: Super Contributor
timestamp: December 06, 2016, 04:14:05 pm
content: Candies!I'm doing TCR testingtoo, but except it being painfully slow, nothing strange so far. Need build separate metal slug thermal unit for faster resistor testings.

author: mimmus78
author_rank: Unknown
timestamp: December 08, 2016, 02:40:07 am
content: Well really is not strange ...As Dr. Frank wrote somewhere after some thermal stress you need to leave the resistor rest for many hours to make them recovery some thermal caused hysteresis ... only in this case you can get the real TC of the resistor. I found some resistors have more than 20% of TC improvement after waiting 16 hours. I also found this hysteresis to improve with thermal cycles ... than more you therm cycle the resistor than more it gets better.Unfortunately I don't have so much data to have a clear idea of what is happening ... and collect this will take forever.Hope I can post some chart in some days.

author: TiN
author_rank: Super Contributor
timestamp: December 08, 2016, 04:17:39 am
content: QuoteJust two weeksData DSVs:Ramp up,Ramp down.

author: Andreas
author_rank: Super Contributor
timestamp: December 08, 2016, 07:15:51 am
content: What resistors did you use?Hermetically or with plastic housing.Guess with this long time there is some humidity influence.And some creeping effect if plastic housing.With best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: December 08, 2016, 11:45:18 am
content: O men two weeks is the definition of "this will take forever" ... I think with slow ramp up you can go with just 24h.Lucky you that have the scanner card ... I already finished my budget for the next couples of years so I can measure only one at time.

author: TiN
author_rank: Super Contributor
timestamp: December 08, 2016, 12:23:55 pm
content: No scanner card used in this case. Three separate meters are the jedi way. Need to get moar 8.5-digit meters, so I can test 4 resistors together!I tried faster ramps, but it's just too small margins to tell what change from what.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 08, 2016, 05:21:43 pm
content: If it just for the temperature effect one could go faster and maybe also do a continuous ramp instead of the step like profile. However it is not only temperature that effects the resistors, but also indirect effects, like expansion / shrinking of the PCB which can be in part due to humidity effects. So it is not easy to get a pure temperature effect. Also Temperature gradients can have an influence - this is likely much of the overshoot seen on temperature steps.A scanner will add some errors - so for highest precision it is better to use the DMM directly. It somewhat depends on the required resolution and noise: one might get away with a good scanner. At least with the slow temperature profiles noise is not that critical - so it is only a possible longer term error (e.g. thermal EMF of the scanner) that is a really problem. On he other side a scanner could reduce some of the thermal EMF errors by reversing the resistor.

author: TiN
author_rank: Super Contributor
timestamp: December 09, 2016, 03:34:53 pm
content: Since most of my little modules PCBs happen to have same width, I decided to make an hermetical service enclosure for additional thermal testing.We talked about this wild idea few pages ago, so this will also be used for that.It's simple copper tube 42mm in diameter, 130mm length with caps. Material of choice is copper, so I can solder it to make gas and liquid tight. This is required to allow submersion into LN2 dewar, while keeping cryogenic liquid out of direct contact with PCB module inside the probe.Inner tube wall has two slots to support and hold PCB, which just slides in. Caps are easy to solder to the tube, longer copper thin tube is 10mm OD, to have power, signal wiring and cabling escape the dewar and probe PCB.I'll also test low-noise preamps in this chamber once they ready, to see how temperature affects the noise figures.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 09, 2016, 04:14:03 pm
content: Very nice TiN. Looking forward to some real "low thermal" copper put to the test.Any plans on controlling condensation?

author: TiN
author_rank: Super Contributor
timestamp: December 09, 2016, 04:24:43 pm
content: It's easy to pressurize inner volume with nitrogen. Just after nice few hours prior bake with everything inside the probe.First test would be just blank PCB with thermal sensors to measure curves and temperature change speed. Perhaps by using smaller PCB with bit of insulation and internal heater I could also adjust temperature in wider range.

author: David Hess
author_rank: Super Contributor
timestamp: December 09, 2016, 07:41:40 pm
content: I have used liquid nitrogen cooled environmental chambers before with the board exposed without any protection. Once my boss came in while I was doing a cooling test to destruction and asked how cold it was. "I do not know because the thermometer only reads down to -199F but since the liquid nitrogen is pooling inside the chamber and the board is sitting in it, I assume -320F." The precision amplifier and comparator circuit never failed and continued to meet its specifications.Aluminum electrolytic capacitors (and I assume wet tantalum capacitors but I never tested them) obviously do not function at such a low temperature but the design recognized this and used ceramic and solid tantalum capacitors which had no problem. None of the common plastic or glass packaged surface mount parts I was using had any issues but I expect that thermal cycling would have eventually broken something. The total error of the LT1013 class operational amplifiers I was using increased but not in any unexpected way.For a hermetically sealed design using copper and tin based solder, how quickly doestin pestbecome a problem? Is this an application where an antimony or bismuth bearing solder should be used?

author: mimmus78
author_rank: Unknown
timestamp: December 12, 2016, 03:00:18 pm
content: So I managed to get my own way of measuring TC of resistors working in a reliable and automatic fashion.I use what I consider an easy to build but "sophisticated" method to heat the resistor that leave almostjust few seconds of lag from the temperature measurement point and the R variation. As you can see onthe second chart TC curve is almost a straight line ... this should means temp. and res. variation track veryclosely. I still have to check some parameters to prove this method is deftly OK and than I can describehow I did it.Anyway apart from heater, the measurement are done with a K2001 in 4W configuration with offsetcompensation to avoid thermal EMF to upset readings.My thermal cycle consists in heating from room temperature to room temperature + 5°K and stay there forsome minutes, than increase other 30°K (and stay at this point for more minutes) and than back to initialroom temperature + 5°K (and rest there for more other minutes). Rump up and down are made almost asfast as I can. The rump up is 1°K per minute circa and rump down is a little slower than this.All measurements where done with stable/stabilised room temperature with a max variation of 0.5° C.I started checking some UPW50 few days ago and I get10.005,05 @ 26°C10.006,02 @ 56°Cthat is something like ~ 3,2 ppm/K that is also right in the typical specs of the resistors.The strange thing is that I found something physical is amplifying the TC effect, I observed that after heatingthe resistance value always "overshoot" and after cooling down it undershoot. I got more 0.1ppm/°K ofdifference if this parameter is measured before or after the rest period (maybe also 0.3 ppm with someresistors). 0.1 ppm/°K is not much if you are matching 3ppm/°K resistor for the LTZ1000 divider, but I'm stillcurious what is it. Anyway if you find a 1 ppm/°K resistor this 0.1 pmm/°K became very important and cancause significant error in TC measurement (I think this effect will be reduce with low TC resistors but this isstill to be proved).So the TC of this resistors seems to be a combination fo TC of the wire and TC of some physical stressapplied to the bobbin during heat and cool down cycle with the latter requiring more time to settle downthan just plain TC of EVANOHM.I read Andreas thread about TC of resistor, but I cannot find any measurement where the DUT was leavedat the new temperature to rest for some hour. Because of this I cannot tell if this behaviour compare the thechart Andreas proposed in his thread or not.I found also many of this resistor seems to go down in value after many thermal cycles. This last went down of20 ppm, but this drift can also be caused my meter that is not stable. I have to remember to check multimeteroffset reading against my calibrator (that has some VHP resistor inside as reference) at beginning and endof measurement to be sure shift is of the DUT and not by ME.Any comment is appreciated.DomenicoPS: just noticed on second chart that measurements gets noisier at the end of heating a cooling process... so it can also be my measurement technique that is wrong.PPS: just realised that at the end of the heating/cooling cycle there are a big number of points becausetemperature variation is more slower than in the middle of the chart ... so if we use temperature as X axisit's normal that it appears to be more noisier at the end of each cycle.

author: Andreas
author_rank: Super Contributor
timestamp: December 12, 2016, 07:43:49 pm
content: Hello,pictures please.And I think that the "warm drift" is due to some relaxation effect (or humidity effect) of the epoxy.With best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: December 12, 2016, 10:08:41 pm
content: -- Andreas --initially I was thinking too to humidity. But I run more than 20 cycles on this resistor and this relaxation effect at begin and end of the cycle is almost exactly the same day after day, from the first cycle to the last one. Unless it's a sponge I guess it cannot be so sensitive to humidity.-- as for my setup --it will run all the night to trace the next resistor so I'll try to take some photos tomorrow evening when I will exchange the resistor under test. I hope to have some time to describe why this elementary setup works so well and make a post ... this will be good if you would like to reproduce the same process. In any case, if I will not find the time to do the post, I will just post the photos on your post.I have some initial conclusions from my initial TC exploration of this UPW50. Almost any value I tested is +2.2ppm to +3.2ppm except for the unfortunate case of the 1K resistor that are all -1ppm.Still to be determined if they drift apart ... I will check my multimeter in a few days and with all data collected I should be able to track any drift ...At the end if I use this three resistors:2K (+3ppm)10K (+3.1ppm)1K (-1ppm)for the ts divider of the LTZ1000 I get a total error of just a little bit more than 3.2ppm/°K.This value is than attenuated by a 75 times factor to the Vzener and it become less than 0.05 ppm/°K. This value should be not too much but it's still something to consider in the hole error budget.I ordered another 1K UPW50 resistor from another supplier in the hope to get one with positive coefficient (it should be here tomorrow).I think in any case I will assemble the KX reference this week end with what I have ... than maybe I will exchange this 1K resistor in future when I will have one with some positive coefficient.

author: mimmus78
author_rank: Unknown
timestamp: December 12, 2016, 10:14:41 pm
content: Andreas: I think I lost from the LTZ1000 thread why the LT2057 was discarded at the end by you, may you just repeat the reason?

author: Andreas
author_rank: Super Contributor
timestamp: December 12, 2016, 10:31:47 pm
content: Hello,my UPW50 were all in the range of +0.6 .. +4.8 ppm(so with a relative large stray from device to device).https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg503546/#msg503546with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 12, 2016, 10:50:44 pm
content: Quote from: mimmus78 on December 12, 2016, 10:14:41 pmHello,It wasn´t me.I have 2 references running with LTC2057 (#5 + #6) against 2 references with LT1013A in CERDIP8 (#3 + #4).Up to now no winner. The lowest ageing drift seems to be on #4 + #6. (with same datecode of LTZ1000A)If I look closer to the data:the devices with LTC2057 can be operated at lower voltages.and have (by accident or systematically?) lower T.C. (before adjustment with R9).with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: December 13, 2016, 10:31:10 am
content: Quote from: AndreasI added another sample but I think you get the point ... actually I measured hysteresis in the first cycle is 33% to 50% of TC.Maybe we need to change test procedure:- What happens if we use only 10°K as thermal cycle with max 1°K per hour of dt?- Does hysteresis effect is reduced with lower and slower thermal cycle?- If we use fast and slow thermal profile, does resistor settle down to the same value after 24h resting?To test latter point I was thinking to do:- move from t.amb to t.amb + 8 with 1°K x hour- rest there for 2 hours- move from t.amb + 8 to t.amb + 4 with 1°K x hour- rest there for 3 hours- move to t.amb + 40 with more than 0.5°K x minute- rest there for 1 hour- move back to t.amb + 4 with more than 0.5°K x minute and rest there for many hours and check what happens

author: TiN
author_rank: Super Contributor
timestamp: December 13, 2016, 05:02:48 pm
content: Alright, long story comes to and end, module was shipped and on it's way to the end userArea around reference chip filled with isolator and enclosed into metal cage for shielding/air draft protection.Similar on the bottom side.Final assigned value:+7.1637446 VDC, +/-0.6ppmat +24.0 °C ambient.Pre-shipmentdatalog captureproven stability within 0.5ppm over 5°C ambient temperature variation.Hope we hear from new happy owner in few months, once module make it's way into Belarus

author: mimmus78
author_rank: Unknown
timestamp: December 13, 2016, 07:51:52 pm
content: Not nice ... but sure enough stable.Just realise my thermal chamber used for resistors TC with its 3 cubic centimetres volume is too small for testing this modules :-)PS: a 3458A is near to begin another journey to his new destination

author: Kleinstein
author_rank: Super Contributor
timestamp: December 13, 2016, 09:11:52 pm
content: A not so nice professional look could be an advantage, when it comes to customs.For the hysteresis, there are several possible effects to cause is. Some of them, like uneven thermal expansion might be influenced by temperature gradients and thus by the speed of temperature changes. But generally I would not expect a big influence of the heating rate. The rate of cooling from high temperature might have an influence, as relaxation processes might get increasingly slow on cooling. So once you are something like 40 K below the last temperature where the system was in internal equilibrium, it may take very long to catch up and may not reach that state even after days of waiting. Fast cooling from high temperature can make a difference - I know it does to the properties of epoxies, when cooling from above 100 C.

author: mimmus78
author_rank: Unknown
timestamp: December 13, 2016, 11:01:09 pm
content: Quote from: Kleinstein on December 13, 2016, 09:11:52 pmI started another very slow test this night 1°K per hour slope and it seems I'm getting completely different values. I too didn't expected so much difference ... let see tomorrow what it turn out after temperature is 10°K up. Actually with 5° K delta is only 0.2ppm/°K VS 1ppm/°K I got yesterday I cannot explain all this difference. Also Edwin explained many times that fast or slow temperature delta should not make much difference with a good resistor.

author: dr.diesel
author_rank: Super Contributor
timestamp: December 14, 2016, 04:32:33 pm
content: Look what showed up today!Digikey stuff has been here for a while now, just waiting on resistors.Thanks again tomimmus78andTiN

author: TiN
author_rank: Super Contributor
timestamp: December 14, 2016, 04:37:07 pm
content: And finally I got around and updated Gerber files to revision B03. Nothing serious, just widen some gaps, thicken few traces and uodated silks/masks and bit of plane pours for more lax DFM. Gerber files hosted the same place as before.No plans to order/build boards yet though, I need catch up on few other things and build reliable noise measurement setup.

author: mimmus78
author_rank: Unknown
timestamp: December 14, 2016, 08:23:19 pm
content: The slow rump up give me exactly the same TC results in the 26-56°C temperature points as the fast rump up so my result are as we all expected.What was different was that the slow rump up give you the possibility to better appreciate and measure TC with better accuracy at every °K.The fist 10°K the TC was of -0,38ppm/°K and than it accelerated step by step to -1.6ppm when the temperature was approaching the 56°C.This has fooled me yesterday in thinking I had completely different data because I made preliminary estimation of TC only on the first 10°K.I will continue to do experiments ... I'm still not convinced what are those resistance recovery that happens when after a thermal cycle weleave the DUT rest for many hours at the new temperature. I suspect those recovery are physical compression/relaxation of the resistoritself and that they also cause the resistor to drift.

author: TiN
author_rank: Super Contributor
timestamp: December 28, 2016, 11:56:42 am
content: I've heardmember SvanGoolgot his boards manufactured, using B03 latest Gerber.He shared this photo with me:Guard ring bit overly thin, but that shouldn't affect anything much.Btw, anyone get references based offmimmus78PCBs going?Happy holidays everyone!

author: SvanGool
author_rank: Regular Contributor
timestamp: December 28, 2016, 01:32:09 pm
content: You can find TiNs KX-ref PCB Version B03 here:https://oshpark.com/projects/HfKcqjV3at OSH Park (with TiNs permission).They are still UNTESTED.These are the standard 4-layer boards with ENIG(gold)-finish.The minimum order at OSH Park is three boards, these cost in total $49.80 ($16.60 per board), including standard (international) shipping, excluding any potential taxes or other costs.

author: mimmus78
author_rank: Unknown
timestamp: December 28, 2016, 04:00:49 pm
content: TiN many buddies received boards, but nobody still built it in public. I'm going to build first sample soon. I received Edwin resistors yesterday (3 sets) ... as soon as I find 2 dammed resistors for the temperature set divider with same tempco I will start.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: mimmus78
author_rank: Unknown
timestamp: December 28, 2016, 11:39:45 pm
content: Ahh forget to order couple of caps and the TC resistor ... and mounted second op amp reversed!Inviato dal mio Nexus 6P utilizzando Tapatalk

author: plesa
author_rank: Frequent Contributor
timestamp: December 29, 2016, 12:01:01 am
content: Sooner or later you will needs decent enclosure. I used this onehttp://www.ikea.com/se/sv/catalog/products/40288354/It is better than polystyrene box used in past.Grounding of enclosure is made by cu tape placed over the gasket.

author: mmagin
author_rank: Frequent Contributor
timestamp: December 29, 2016, 08:23:38 pm
content: Well, I'm finally giving into serious volt-nuttery. It seems like once I manage to obtain resistors I'll probably be building a couple of these. I'll post updates, and I will probably be interested in the unofficial calibration service. At the moment, this is all better than the best meter I have, an HP 3457AIs it reasonable to consider the LTZ1000A and precision resistors water washable? My inclination is toward using entirely water soluble flux, initially washing with warm water and detergent, then multiple rinses of distilled water + isopropanol.

author: plesa
author_rank: Frequent Contributor
timestamp: December 29, 2016, 08:46:42 pm
content: Quote from: mmagin on December 29, 2016, 08:23:38 pm3457A is quite good DMM. If you purchase in future 3458A you will know how to operate within few secondsI can hook it to LTZ setup to provide comparison between 3458A nad 3457A. For example K2001 is noisy but stable, 34401A are silent but fluctuating with temperature/humidity.I will not recommends any washing nor immersing in water. Use IPA only. Clean by brush and small amount of IPA. Some of resistors are sensitive to humidity. LTZ board(s) do not need to be superclean.

author: mimmus78
author_rank: Unknown
timestamp: December 29, 2016, 08:46:54 pm
content: And here you go. Initial tests with brutal TC estimation tell me all assembly is 0.1 ppm/°K.

author: mimmus78
author_rank: Unknown
timestamp: December 29, 2016, 09:17:25 pm
content: plesaI used 12K/1K as temperature set poit for the LTZ1000 ... what is temperature delta vs ambient temperature inside this IKEA thermos?Wondering if it will be too much high temperature during summertime (here gets as hot as 30 degree during summer time).

author: mimmus78
author_rank: Unknown
timestamp: December 29, 2016, 09:20:06 pm
content: Anyway during this days I discovered my K2001 is just 5ppm apart from the 3458a on the 10V range (the other ranges are much apart).Not bad considering last calibration (sticker) is 15 years ago.

author: plesa
author_rank: Frequent Contributor
timestamp: December 29, 2016, 09:36:54 pm
content: Quote from: mimmus78 on December 29, 2016, 09:17:25 pmI'm using same ration sot temperature setpoint (~40°C), but I'm not measuring temperature inside IKEA thermo. That can be interesting.This vacuum thermo flask is good because it is also humidity tight. With some 3D printed holder and cap over LTZ1000 it is ready for transport.I do not think the heat generated by LTZ mainly will be problem.

author: Andreas
author_rank: Super Contributor
timestamp: December 29, 2016, 09:57:26 pm
content: Hello,you should detect the upper temperature limit when doing final T.C. check (with final housing)of the LTZ cirquit over the temperature range of interrest.With best regardsAndreas

author: VK5RC
author_rank: Unknown
timestamp: December 30, 2016, 11:14:41 pm
content: Re temperature of LTZ in insulated-enclosed environment.I have been using an old reference board from HP (ex 3458), it is in a metal box with insulation inside the box and some over the LTZ. Tied to the board close to the LTZ (about 6-8mm away) is a Fluke temp probe (brown cable) also inside the box is a linear PSU which drops from 18 to 15V at about 30mA - so total power inside the metal box is about 0.5W. The metal box is inside a plastic tub (further insulation) see photos below. If ambient is 17-25C (my thermal limits!) it takes about 1-2hrs to stabilise in temp but is between 30-31C .Grey cable DC inBrown Fluke temp probeGreen DC outEdit; Box is now shut and cables routed through small hole

author: Kleinstein
author_rank: Super Contributor
timestamp: December 31, 2016, 09:00:49 am
content: If the whole ref circuit is inside a relatively well insulated box, the LTZ internal heater (and the driver transistor) will also work to stabilize the temperature of the whole circuit. It depends on thermal insulation and will not be perfect, but one could expect something like having a circuit temperature at something like half way between the fixed internal temperature and the room temperature. So temperature variation would be reduced by a factor of 2 in this example. To use more of the effect, a slightly higher temperature set point and better insulation could help. Also the amount of insulation directly around the LTZ1000 as an influence - more insulation is not always better.It is a good idea to have an extra temperature sensor somewhere at the circuit to see if the temperature for any reason is too high. With such an insulated bottle, much of the heat loss is at the top and through the cables.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 09, 2017, 12:03:22 pm
content: Quote from: mimmus78 on December 28, 2016, 04:00:49 pmI just got word from Edwin that my resistors have shipped! I bought enough to populate 3 KX boards, leaving 2 more for future thoughts/lessons learned. I have all the other necessary components already.

author: mimmus78
author_rank: Unknown
timestamp: January 09, 2017, 12:15:22 pm
content: Almost finished experimenting with mine ... I'll keep it running for some days and than publish what came out.In all this Odyssey I learned a lot and got some ideas for the next one.1. Always buffer the reference. I risked to short it many many times in the most not obvious ways. In my case I think this buffer also kinda lowered some noise (but I still have to check measure and confirm this data).2. I think to get better long term stability and noise is mandatory to add some sort of oven too. This double oven (one in the LTZ and this other) will improve TC and keep resistor at a stable temperature. From my little experience with TC of resistors, keeping resistor at the same temperature will reduce long term drift. But than you have to keep it on always or otherwise the bigger temperature excursions can create more drift/hysteresis to those resistors than the normal t.amb variance.3. LTC2057 was causing more than 1ppm jumps depending on what power source I was using or if I used shielded leads or not. Replaced opams with ADA4522 and now it's 1 to 2uV delta swapping power supplies or using different leads. The most of the offset was caused by the opamp driving the zener. Changing the opamp for the heater didn't change anything really measurable. Using the same LTC2057 as buffer seems to have a very little influence. Anyway I'm still not convinced about this drift was caused by LTC2057 ... another LM399 based reference is using the same chip and seems to be not susceptible. Unfortunatelly noise of LM399 is much higher so making such evaluation needs much more care than I really wanted to put in the measurement.

author: Andreas
author_rank: Super Contributor
timestamp: January 09, 2017, 08:07:28 pm
content: Quote from: mimmus78 on January 09, 2017, 12:15:22 pmGood to know that the ADA4522 behaves better.I have solved the EMC-issue on the LTC2057 with a 100nF cap.(but also use a 22R series resistor and a capacitor in the feedback loop).https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835With best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: January 10, 2017, 08:08:32 pm
content: Well yes slightly better ... I solved susceptibility with Siglent power supply (drift passed from 10uV to 2uv) and apparently reduced problems with leads ... but now I had Idea to test with very short twisted copper ethernet cable (15cm) and I'm getting 10uV down drift. Deftly need to try your caps and resistor for EMC mitigation after buffer. See you in a few hours.

author: mimmus78
author_rank: Unknown
timestamp: January 11, 2017, 11:02:18 am
content: It's not EMC the buffer just follow what it find on input ... still investigating

author: dr.diesel
author_rank: Super Contributor
timestamp: January 12, 2017, 02:57:24 pm
content: First board up and running!(12k/1k ratio, Edwin resistors)

author: splin
author_rank: Frequent Contributor
timestamp: January 12, 2017, 11:52:32 pm
content: That's a remarkable meter you used to measure the reference - apparently with maximum and minimum voltages displayed at 7 1/2 digits, uV resolution, but manages to calculate the peak to peak to a further 7 digits, 6.8025031uV p-p. 100 femto volt resolution on a 10V range is quite incredible.Too incredible obviously. The difference between the displayed max and min values is 7uV. There may be another digit undisplayed so 6.8uV p-p may be plausible even if the .8uV digit is mostly noise. But why would the developers choose to display a further 6 digits of completely bogus resolution? How could the value have been derived?

author: mimmus78
author_rank: Unknown
timestamp: January 13, 2017, 12:57:54 am
content: What's the meter?Inviato dal mio Nexus 6P utilizzando Tapatalk

author: mmagin
author_rank: Frequent Contributor
timestamp: January 13, 2017, 01:09:24 am
content: Quote from: splin on January 12, 2017, 11:52:32 pmSomewhere that programmer's high school science teacher is cringing.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 13, 2017, 01:19:19 am
content: untruncated calculation precision is not uncommon!

author: splin
author_rank: Frequent Contributor
timestamp: January 13, 2017, 02:46:02 am
content: Quote from: dr.diesel on January 13, 2017, 01:19:19 amVery true. But in this case what calculation is involved in working out the peak to peak value other than subtracting the minimum from the maximum values? That doesn't create any extra digits, spurious or not, unlike mean and standard deviation calculations.I'm struggling to think of possibilities but I guess it's conceivable that they could be allowing for the meters own noise by adjusting the maximum and minimum readings by subtracting/adding the meter's known peak noise (adjusted for range, integration time and filtering levels etc.). That could make the peak to peak readings more accurate - on average - but could under/over read true maxima and minima. This seems very improbable though given that the benefits/detriments would likely be very dependant on the statistical properties of the signal being measured.So where could those extra digits have come from? I'm sure there's a simple explanation but I'm not seeing it at the moment.

author: TiN
author_rank: Super Contributor
timestamp: January 13, 2017, 04:14:47 am
content: dr.dieselBeauty. Now add some foam protection around both sides of LTZ, drop everything in the metal can, and let it sit for a month or two powered (about enough time to build a DIY thermal chamber for future tempco tests). Then we can see some data.I can't say I particularly like these standing way to mount those resistors though. I know why you did it, but not sure if that cause issues due to uneven thermal gradient over resistor body (PCB side leg is much shorter, with much larger thermal mass on it). Usually when using axial resistors, I bend legs in "radial-way" and mount them with body parallel to board.Maybe if you plan building more boards, you can try that so we can compare?splinI'd expect programmers just implemented standard FP math without actually thinking much how real are the numbers, be they down in the white noise, or have real meaning. Doesn't bother me much though, as you already know what is real and what is not.

author: Andreas
author_rank: Super Contributor
timestamp: January 13, 2017, 06:36:09 am
content: Quote from: dr.diesel on January 12, 2017, 02:57:24 pmMhmm,7uVpp for a source that should have 1.2uVpp.Which NPLC?Is it the DMM or the zener?Does the heater run properly?with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: January 13, 2017, 07:50:14 am
content: So time to publish some result.It seems I almost sorted out all my problems with EMI and leads and power sources ... now no matter what I do, I do not have anymore super large drift of the output (almost 2ppm before) the max drift by changing swapping all this conditions is now usually 0.1 or 0.2ppm with the larger one of 0.3 ppm when I turn on a programmable power supply.I will explain all I did in a further post, I think I can live with it for now.Anyway here is last chart from yesterday when I applied heater caps ... (RMS noise went down of almost 100nV).The image is very large ... so it's better you open in another window.The red line at the bottom is RMS noise. 0nV at base of the chart and 250nV at every division, RMS is calculated on last 100 samples.The tin green line that is my room temperature.The green dots are the single readings (100NPLC with autozero sync)The blue line is the median value of the previous 100 readings.The orange dashed lines are the temperature of last ACAL and the internal temperature of the 3458A (temperature are chart with -10°K to make the chart more compact)The last black line is internal reference temperature.The chart is one 10uV large ... so 1.4 ppm.PS: first drop in the chart is me changing leads.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 13, 2017, 11:10:01 am
content: Quote from: Andreas on January 13, 2017, 06:36:09 amYeah, don't think anything of this, it was only a test power up, just to make sure no shorts, it works, I didn't screw up etc.TiNTwo more boards will be finished today, one I will build like you describe (parallel to the board), same 12k/1k ratio, and the 3rd with 15k/1k ratio, both Edwin resistors.That will leave two spare boards, I was thinking of building one with off the shelf DK resistors, to demonstrate what's possible without special ordering. Unsure and taking suggestions for the 5th.My 3458A mods/SRAMs/re-cap is complete and it's headed toCalMachine'snext week for calibration.I'm also happy to help/provide testing to others.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 13, 2017, 04:08:01 pm
content: Two more complete.Had one small issue with the 3rd board, heater wasn't working. Turned out to have a very small piece of debris in the indicated area shorting pin 1 of U6 and C9, flushed it out with a soft brush and all is good.I'm still debating on the enclosure, was originally going to gut my old 731A and install ~3 boards or so, haven't decided yet.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: January 13, 2017, 05:51:25 pm
content: Just a head's up and suggestion: You're using '2057 op-amps which have a tremendous amount of input current noise compared to LT1013, in addition to SMT package which make very good board stress detectors. Beside excess current noise on your extra-long board traces, that additional mechanical stress on the LTZ die caused by AC current noise -can- cause stability problems long term, be aware. It can also cause die breakdown in extreme cases. We have seen this effect in other circuits as well, that's why we quit using'2057's in almost all test circuits a few years ago. The '2057 is not a cure-all for everything, not by a long shot. It can work, but not really what you want for very long term stability as an LTZ current driver.See page 18 of the '2057 datasheet, and then start really measuring the current noise compared to a '1013, and you'll see what I mean. If you want to keep shaking your LTZ die, the '2057 is just the part to do the job!The -only- recommended op-amp for use with LTZ is the LT1013 (recommended package for best performance is DIP version, ceramic is available too), and there is absolutely no reason NOT to use one, as others have noted here several times. Your circuit will be just as stable - the slight Vos of the '1013 will have virtually no effect on output. If you call LT applications, they will strongly advise against the '2057 as well if you are going for high stability, low current noise and low radiated noise on inputs and power busses. The best defense against noise is to NOT generate it in the first place.Watch out on those surface mount caps also - not really recommended practice on a precision Vref. They are very microphonic and will show you board stresses as well.Just something to be aware of when you mount these boards up. I would also be careful of 12k over 1k. That's pretty cool. We've never had issue with 13k over 1k or even 15k over 1k - plenty of those are perfectly stable after decades. When I say stable, that means they still don't move a ppm per year. Which is the realistic limit of measuring any volt-referenced anything at a cal lab. The overall stability of your LTZ - all else being the same and correct - will be swamped by the crystal lattice stresses in the die itself (and where it was cut from the wafer), and there isn't anything you can do about that except wait. A. Long. Time. for stresses to spread and stabilize. It will be pretty close after a few days run time, but it takes exponentially long to expose the true story of each LTZ when you're chasing down into low PPM's.As others pointed out: Resistors standing on end is about the last thing you want for low thermal difference between leads, that could also be a source of that huge noise you're seeing on output. Of course the LTZ has to be kept covered. With that flopping around in the breeze like that you will definitely see a lot of noise just from airflow around the device.After soldering, do your final measurements at least 8 to 12 months out at least and compared to 732b's or 732a's if you have access to several - at least three. No DMM is good enough to tell you the whole story with these LTZ's. Nulling against a known stable reference will give you a better picture of stability. The boards you just made are infants and need a -very- long time to become stable again. You might see some stability after a few months but we cook 'em at least 12 months or longer if the application is critical.Time will tell.Good luck!

author: Kleinstein
author_rank: Super Contributor
timestamp: January 13, 2017, 07:30:51 pm
content: Form the pure specs the noise current of the LTC2057 is not that bad: like twice the LT1013 at 1 kHz and maybe even lower than the LT1013 in the sub 1 Hz range as the current-noise of the LT1013 will go up there. However bias currents and possibly current noise could be higher when working at the low 0.7 V common mode voltage.The problem is that the current noise of AZ OPs is not normal, mainly low frequency noise, but there is also a significant higher frequency background. Performance of AZ OPs depends in a more complicated way on the input impedance, than just giving a current noise number. So depending on the sensitivity of the circuit, there can be extra trouble.There is just very little to gain in using the LTC2057, but a lot of possible trouble. The LT1013 is perfectly good enough - if you for some reason can't get one form Linear, use the more or less direct replacement from Ti. Before changing the OPs there are other points in the typical LTZ1000 circuit, e.g. temperature regulation at low power (this could be a issue with a 12K/1K divider), the 400 K resistor for TC compensation, EMC, lower sensitivity to the temperature set-point and the thermal design.You need to cover the LTZ1000 and have a case around the whole board before you can really tell how good it is working. This is especially true with the way the resistors are mounted.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 13, 2017, 07:46:11 pm
content: Great points above, thanks!The two 12k/1k boards are intentionally borderline, the 3rd is 15k/1k, and the remaining two will be 13k/1k most likely, all with the 2057.I think then I'm going to build (5) more, but with a layout that will properly accommodate Edwin's 802 series and the DIP 1013, perhaps a few other mods.Fun fun, now all I need is a Fluke 734,

author: Kleinstein
author_rank: Super Contributor
timestamp: January 13, 2017, 08:51:51 pm
content: If it is for the boards already made, there is the LT1006 as a single version of the LT1013. So there is an easy way back from the LTC2057 idea. As the chips are relatively far away from the LTZ, the SMD form may not be that bad.Also not all of the LTZ1000 are equal: the TC without temperature stabilization (but still at the high temperature) can be quite different. To a first approximation the rather good temperature stabilization covers this, but those units with a lower intrinsic TC will be less sensitive to drift in the divider that sets the temperature. This could be important if you compare performance. If you use more of the LTZ1000 at different temperature or current, it might be even worth picking the right ones for each temperature / current combination. Having half the TC for the chip could be as good as half the drift for the divider.

author: Andreas
author_rank: Super Contributor
timestamp: January 13, 2017, 09:16:50 pm
content: Hello,Quote from: Kleinstein on January 13, 2017, 08:51:51 pmwhat differences did you measure at the unstabilized T.C. ?Quote from: Kleinstein on January 13, 2017, 08:51:51 pmWhere do you get those devices with a halfed value of unheated T.C. ?Up to now I had less than +/-5% variation in unheated T.C.With best regardsAndreas

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: January 16, 2017, 08:20:23 pm
content: Quote from: Kleinstein on January 13, 2017, 07:30:51 pmKleinstein touched the tip of the iceberg here, and after you spend some bench time testing AZ amp like '2057 and their ilk, you realize how close the datasheets come to what Mark Twain was talking about: "There are three kinds of lies: lies, damned lies, and statistics."The datasheets rush to show you the apparently low current input noise of these things, and then try to not really mention what's really going on with transient input current noise happening at the amp's chopper frequency, and then of course at harmonics up from there.When you look at the input current chopper noise of a '2057 or similar - just from the datasheet - it looks like maybe you still have maybe double the input current noise of an LT1013, but still low. NOT EXACTLY! How about 100X to 600X the current noise when you look at those current spikes in detail! At first you thought you were talking about some pA or nA of current noise - but suddenly you realize you got input current spikes of some uA pounding around your sensitive circuit!If you look at the LTC2057 datasheet, do you see how thecurrentinput noise AT the chopper freq. isn't mentioned a lot?So you take an LTZ1000 - which wants a QUIET QUIET QUIET and un-eventful current flow, and in return coverts that to a stable voltage across it's zener diode + transistor Vbe voltage drops - and when you slap a clock-driven, commutation switched auto-zero op amp in there an you get BLAM BLAM BLAM current spikes applieddirectly to the LTZ die- especially from the inverting amp input. Those sharp, short current spikes get converted into mechanical stress waves inside the substrate crystal lattice. It's like you're hitting the LTZ die with a very small, but definite hammer effect of an AC current pulse train. These disturbances in crystal stress will start at Chopper at frequency, but by the time they reflect and modulate around the edges if the die you'll see detectable stress acoustics up into the low Mhz region.Not to mention the other thing that happens with AZ amps: Any trace length and enclosed loop area on the amp inputs will become antennas for noise radiation of what otherwise was a very quiet, beautiful, pristine analog circuit. Especially if you have "Crop Circles" type traces or "Voodoo Slots" around the LTZ (Not complaining about TiN's board at all, but we've never seen -any- improvement with those types of design tricks - but can and does pickup and radiate noise more when traces are too long and not very efficient layout) Just when you thought you had a quiet analog board - that AZ amp inputs and power rails will be splattering ~100kHz or whatever chopper frequency hash around the area. It is a low current, but it can have enough energy to mess up nearby sensitive circuits for sure if you're not ready for it. In some cases those AZ current spikes over time can drive a crack in to the crystal substrate of whatever they are connected to - usually if there was an edge defect to begin with.For these reasons above (and because an AZ amp offers virtually no benefit to an LTZ current driver) is why LT does NOT recommend the use of an Auto Zero type amp for an LTZ. There are other applications for an AZ amp, but this definitely is not one of them.Remember: Plenty of workhorse 3458a's out there with ppm / yr drift rates down in the Low-PPM mud, and virtually completely stable for decades without a fuss. There are no AZ amps, slots or crop circles required. If the basic datasheet circuit is followed with a good, reasonable, efficient compact board layout - this is very hard to beat for max performance and reliability. There may be a slight thermal gradient on the non-fancy board, but if the gradient is stable (it usually is inside an enclosure) there is no effect on output. You keep air drafts away but do not OVER-insulate the LTZ board, which is just as bad as no covering at all (because the heater circuit can't servo correctly in a near 100% thermal-insulated environment). You select your heater ratio resistors for best performance in YOUR enclosure and application. After that the majority of the drift rate is dictated by the LTZ die itself, and that is beyond anyone's control after the die is singulated from the master production wafer. "It is what it is" at that point and the basic long term drift characteristics are locked in for each LTZ die at that exact moment in time it becomes separated from its siblings.SO: In general, your Auto-Zero amp board will probably work as we're still talking fairly low current spikes input noise, but the use of Auto Zero amps with high-precision LTZ class circuits is really not recommended engineering practice - ESPECIALLY IF you are connecting a precision, sensitive die directly to the AZ amp inputs. For instance an LTZ, photodiode, zener, etc. Also you have to mitigate the chopper noise you're injecting on those op-amp power rails also, which is not insignificant either. Sometimes you realize that it's more profitable from a noise mitigation standpoint to just perform an occasional drift correction by using a conventional amp.For the LTZ circuit especially, the '1013 is the best amp to use, and will offer maximum performance up to and including what the LTZ die is going to give you. It is tailor-made for the LTZ application.For further reading, I suggest taking a look atArt of Electronics Third Edition, Horowitz & Hill - look at chapter 5.10 and the section on precision op-amps. Around page 335 it gets more interesting describing most AZ amp architectures - and their test results vs datasheet noise claims.Also take a look at page 13 here, for a good visual effect of what inputs currents are really doing on a typical AZ-type op amp - this document also describes a test procedure which we've used with some success:https://e2e.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-14-01-00-00-70-21-03/Chopper-Noise.pdf

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: January 16, 2017, 08:25:01 pm
content: I just realized - I suggest this thread should possibly be merged back into the main LTZ1000 discussion, for easier reading for future readers and students of precision Vrefs. This is no longer on-topic of "A Little Jumper"

author: doktor pyta
author_rank: Frequent Contributor
timestamp: January 16, 2017, 09:47:46 pm
content: ++

author: mimmus78
author_rank: Unknown
timestamp: February 13, 2017, 08:46:02 pm
content: So after being unhappy with first KX I build another sample ... but I have exactly the same problems.So decided to scope the output and found it very nosier ... LTZ1000 was measured with spring probe directly to the KX out (minimal ground loop). The other two with long ground loop as I I don't want to tear down the LM399 reference. And for the battery I used crocodile ground clip.Don't know what too think ... but it seems too much noise for a reference.Even if too early, the modules seems to be in spec at 100 NPCL with less than 1uV p2p noise in the short term.This is LTZ1000 module:This an LM399 module:This is a 3V coin battery:

author: Andreas
author_rank: Super Contributor
timestamp: February 13, 2017, 10:23:45 pm
content: Quote from: mimmus78 on February 13, 2017, 08:46:02 pmHello,unless you are having a factor 1000/10000 amplifier in front of your scope you are doing something wrong.(or you are measuring the noise from your scope).Try to supply the references from battery + use a metal cookies box (connected to ground of the scope) for your reference.with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: February 13, 2017, 11:21:58 pm
content: You are right, I was probing directly at KX pcb but I forget to remove leads that where attached to the 3458a.Now without leads is like this ... it seems better than battery. You cannot ask more from the poor Rigol.

author: Andreas
author_rank: Super Contributor
timestamp: February 14, 2017, 05:41:30 am
content: Hello,previously it was 2 mV/divnow its 5 mV/divIs it really better than the coin cell?Or only different scaling?With best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: February 18, 2017, 09:01:02 am
content: Yes Andreas you are right (again). Here is output scaled to 2mV.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: Andreas
author_rank: Super Contributor
timestamp: February 18, 2017, 10:51:20 am
content: Hello,now it looks like noise from a ~60 kHz switchmode supply.nothing I have ever seen from a reference.with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: February 18, 2017, 11:03:46 am
content: Yes I measured same frequency also with battery ... so deftly picking up somewhere. Maybe some coupling with scope power supply.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: mimmus78
author_rank: Unknown
timestamp: February 19, 2017, 07:06:17 pm
content: It seems I'm not lucky with this KX reference.At the end I found way to cure the "power supply brand susceptibility" and reduce EMI to acceptable level (less than 0.15 ppm): the cure was to use LT1006.But I still have huge stability problems. If I swap the zener output on the 3458a (LTZ1000 positive connected to LO and ground connected to positive) I get a difference of many ppm, don't think this is supposed to happen.Things get even worse if I connect swapped out to K2001. With Keithley multimeter even mV digit is flapping. I think there is some capacitive load problem ...Anyone has any idea what is going on?

author: Andreas
author_rank: Super Contributor
timestamp: February 19, 2017, 07:40:29 pm
content: Quote from: mimmus78 on February 19, 2017, 07:06:17 pmHello,the first sounds like a EMI problem.you could test for a capacitive load problem by inserting a 100 Ohms resistor in series to the output.(in high impedance mode of the meters).Usually Op-Amps can withstand directly about 1 nF. (around 10 m of coax).a cure to both effects could be done by modifying the buffer OP-AMP similar to my LTZ1047B design.(series resistor + output EMI capacitor + bandwidth limiting capacitor in the feedback path).With best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: February 19, 2017, 08:19:42 pm
content: The typical LTZ1000 circuit adds some gain to the feedback loop and thus tends to make the output OP even more sensitive to capacitive load than the simple V=1 follower circuit. So it really is a good idea to have some isolation against capacitive load. So even 100 pF could be a problem for that circuit.How sensitive an OP is to capacitive loading depends on the OP. Some are more sensitive than others. Some start oscillation at 100 pF other can stand 10 nF if the rest of the circuit is good. As a relative low power OP the LT1006 is more like a sensitive one and DS curves are for 10 pF - not the more common 50pF or 100 pF.So the DMM input could already be too much.

author: mimmus78
author_rank: Unknown
timestamp: February 19, 2017, 10:10:02 pm
content: OK, with resistor I have following value:Correct connection: 7.13366Correct connection with 120 series resistor: 7.13366Swapped connection: 7.13350Swapped connection with 120R series resistor: 7.13357Swapped connection with 270R series resistor: 7.13360Swapped connection with 1K series resistor: 7.13364So I guess I need to add a buffer ...I build a total of 3 of this references, all had the same problem.With LT2057 and ADA4522 this EMI and capacitive load was even worse.I remember millivolt difference with LT2057 and this leads swapping.And for EMI I can make drift it up to 5 ppm by turning on of off a power supply or a led light.Now the question is, this is happening only to me?

author: doktor pyta
author_rank: Frequent Contributor
timestamp: February 19, 2017, 10:23:13 pm
content: What resistors are You using?One time I had problems with stability of standard Linear Technology application when I changed resistors from bulk foil to wirewound.Probably it was due to prasitic L and C.

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 12:38:59 am
content: So the buffer has solved stability problems with keithley multimeter.Unfortunately not the 16ppm drift by swapping leads. Now I have keitley stable but with the same 16ppm drift (actually 20 on keithley).@doktor pyta: Resistors are wirewound. I was thinking to this too, but then because I can't remember anyone with this problem in the big ltz thread I discarded this hypothesis.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: February 20, 2017, 01:57:55 am
content: For best performance, Linear Tech (and myself) recommend wire wound resistors for best stability and long term performance. If you have such a high noise field that the resistors might be picking some of that up, you should definitely work on reducing the radiated noise field as it could be strong enough to be interfering with the IC's operation as well. Getting rid of noise at the source is always preferred to trying to dampen it out in the circuits you are using. Many sources, such as lamps, power supplies, TVs, laptops, ect., can generate plenty of noise that will be picked up easily several feet away or more and you make a very good antenna yourself. The only source of noise a wire wound resistor creates is normal Johnson noise, anything else is radiated and picked up.

author: TiN
author_rank: Super Contributor
timestamp: February 20, 2017, 04:11:44 am
content: mimmus78I think Edwin is on the money. But I will gather some data for you tonight with normal/reversal operation on few modules, yet I don't recall any mV-level changes like you mention from past tests.What connection wire you use? How long it is? What connectors on DMM side? This is the case when photo of setup actually says more than paragraph of text.

author: Andreas
author_rank: Super Contributor
timestamp: February 20, 2017, 07:00:10 am
content: Quote from: mimmus78 on February 19, 2017, 10:10:02 pmHello,no you are not alone.I also had drift of 3 ppm on a unfiltered buffered output.https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835Others might have lesser EMI around them (your 60 kHz switchmode problem).In your case it seems to be no problem with capacitive loading.In this case the 120 R resistor would be sufficient.After the 120 R resistor you can put a 100nF capacitor against EMI without influence on stability.With EMI problems impedances below 377 Ohms (wave impedance of free air) have usually low effect.with best regardsAndreas

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 12:00:48 pm
content: Quote from: Edwin G. Pettis on February 20, 2017, 01:57:55 amEdwin I don't think I have such high noise, I don't have cheap Chinese stuff turned on during measurement and wifi is far away.One of previous KX, the one with LTC2057 was drifting 1ppm by just turning on and off an old linear Agilent power supply (E3641A). This power supply should not produce so much crap to shift reference of 7uV.I measured up to 5ppm drift on the LTC2057 powered one, depending on what I turn on/off ...The one with LT1006 pass this tests with no measurable drift. Only the bench led light seems to cause 1uV to 2uV drift.Quote from: Edwin G. Pettis on February 20, 2017, 01:57:55 amI'd like to build some circuit that I can send to calibration lab, I can control what is turned-on in my lab, but I cannot control what is turned on in the cal lab.Having a circuit that reject this noise is fundamental to me ... I think 1uV susceptibility is acceptable and maybe inevitable, but if we are on the 1 ppm range this can be a notable source of uncertainty.

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 02:29:20 pm
content: So I removed the buffer for now and got of video of the "Phenomena" with my setup.http://youtu.be/4JAafhXy068Wire is 30cm long copper twisted pair directly connected to 3458a binding posts (so we can exclude it's thermal EMF).>> yet I don't recall any mV-level changes like you mention from past tests.Yes never mentioned this because I discovered this problem with swapped leads just few days agoo.mV changes is with unbuffered version on the K2001 and long wire (more than 1m).I take the following video with very short wire (same 30 cm) and Keithley.http://youtu.be/mCtM-1XaprwEven with short leads drift is still 300uV and also noise become way worse.Counting on what you can see on the video I can say few uV p2p with straight leads (as by Keithley specs) and sort of 100uV with swapped leads.Here you'll find some photos of the PCB.In this last sample I used through hole components because I only planned to build one KX so I brought only one BOM few months agoo.Anyway despite this the same problems where experienced also with fist sample where I used (almost) all components as by part list on TiN KX article.You can see photo of fist KX sample few posts ago. Exchanged components are the capacitors: in this last sample I used ceramic caps forthe one connected at the 70K resistor nodes, CAP FILM for the other lower values and electrolytic for the three high values (47uF).

author: TiN
author_rank: Super Contributor
timestamp: February 20, 2017, 03:47:48 pm
content: Just a side note - board should not be flying around like that, you just asking for trouble and cannot honestly expect any ppm-level accuracy in such test conditions.How about putting board in a small metal box (fixed with foam, not flying freely around)? Tin can from cookies will do, no need anything fancy.There is still quite a bit of work required to make bare LTZ reference circuit board into robust box like 732A/B, which you can ship anywhere.I made a video on investigating your problem, and I think I know what it is. Let's see if you know itEDIT: Uploading video now. You guys make me work!

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 04:25:01 pm
content: TiN fist KX I put inside this metallic box, with some foam to dump temperature changes.Foam was covered with capton to prevent leakage as foam can touch some grounding points (you can see some photos on previous post).I removed some paint from screw-holes to ground all enclosure ... but even this does not worked.This box has also a LTC2057 buffer, a 15V regulator, fuses, ferrite beads at power supplies cable, ferrite beads at the binding posts cables, etc etc.But all this was useless and didn't fix this "phenomena".

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 04:29:01 pm
content: Quote from: TiN on February 20, 2017, 03:47:48 pmTime for some F5 raffica at TiN youtube channel ...

author: TiN
author_rank: Super Contributor
timestamp: February 20, 2017, 04:45:31 pm
content: HereHere we go.

author: mmagin
author_rank: Frequent Contributor
timestamp: February 20, 2017, 07:44:38 pm
content: Is the power supply negative lead connected to earth ground and the 3458A LO terminal connected to the Guard? I can certainly imagine that having an effect when the leads to the 3458A are swapped

author: mimmus78
author_rank: Unknown
timestamp: February 20, 2017, 09:21:03 pm
content: Well it seems pushed on TiN 3458a, but it was/is not on mine.Anyway this isn't the first reference I do this test and they always show 1ppm circa of difference not 30ppm.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: February 20, 2017, 09:59:18 pm
content: I've tried today a reversal on my LTZ1000 reference in the lab, connected to the HP3458A by about two meters of a screened twisted pair cable, the screen is connected only to the Guard terminal on the HP meter. The meter is on a different bench (hence the long cable). The reference is built on the AD5791 1ppm DAC evaluation board from AD. It is unscreened, the board is sitting in the open with only some bubble wrap around it, supplied from a bench PSU. I could not reliably detect any difference in reversing the leads, positive and negative values were the same down to ~1-2uV, in the noise of the system after some small thermal variations settled. I know that my LTZ1000 reference is not ideal (I have a tempco ~0.5-0.8ppm/C due to some cheap SMD resistors used, only the 110 Ohm current setting resistor is a decent WW Ultrohm), but there is no instability, no problems with the polarity reversal and no "jumps". Very quiet though not very temperature stable.CheersAlex

author: mimmus78
author_rank: Unknown
timestamp: February 28, 2017, 02:29:46 pm
content: Few updates on my third KX.I added back the buffer using the same schematic that Andreas posted, plus I added a 1k resistor and a 100nF cap between the zener out and the buffer input.After 1 week and 200 hours ~ of operation it's still stable at 7.13366.If we add a further digits its 7.133662 and this 7.133662 was the initial Vout it stabilised the first day (when the reference was enclosed in the foam).If we stretch a little bit my measurement results with the 3458a, the max delta V measured during this days using: same leads, same power supply and a delta temperature not more than 5°C was not more than 0.2ppm. So if I don't change the measurement conditions this slapped together sample seems enough stable to the point I cannot reliably measure any drift with equipment I have.Kinda puzzled now ... never wanted him to survive more than few tests, but it's alive and until it will show to be stable under controlled conditions it will survive.Quote from: TiN on February 20, 2017, 04:45:31 pmI have some more weird results that are driving me to the EMI direction again, but I need to do more experiments to be sure ...TiN any news about explanation of the drift?

author: TiN
author_rank: Super Contributor
timestamp: February 28, 2017, 06:23:27 pm
content: In case I shown on video it was a ground loop problem. 3458A, gpib cables network, other equipment are making a path for ground currents, which easily upset sensitive direct reference output.Keithley 2304 is particularly bad in this point, as it's has very weak isolation to earth. If you can repeat reversal measurement with battery (even just two 9V square cells with do fine for quick test) and reversal errors gone - same case for you.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 28, 2017, 07:07:47 pm
content: It should not be a DC ground loop problem: The DC output impedance of the LTZ1000 circuit is very low. The OP in the LTZ1000 circuit already make it a kind of buffered output, capably to drive several mAs of current if needed. Output resistance is mainly given by the wire resistance and thus is more in the 100 mOhms range.Thus is would take a substantial (e.g. upper µA range) DC current to cause such a large error on reversal. In this loop there both the isolation of the supply and the 3458 are in series. So even a grounded supply would not be a problem.The problem is more an AC ground loop and sensitivity to EMI. Also capacitive loading to the output is different. The LTZ2057 OP is much more EMI sensitive than the LT1013/LT1006 and also possibly sensitive to output capacitance.

author: TiN
author_rank: Super Contributor
timestamp: February 28, 2017, 07:11:30 pm
content: How is the capacitive loading is different, as same board and connections used in both battery-powered and PSU powered cases?

author: Andreas
author_rank: Super Contributor
timestamp: February 28, 2017, 07:21:04 pm
content: Make the following test:Measure capacitance from +Input to earth ground / and or guardMeasure capacitance from -Input to earth ground / and or guardAny differences?With best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: February 28, 2017, 07:29:19 pm
content: When battery powered there is a low capacity from the supply side to ground, whereas the mains powered supply will have a considerably higher capacity to ground.The capacitive loading seen by the reference output has two parts: the obvious one is the capacity between the DMMs inputs - this does not change.The additional one is from the reference output to ground (especially that of DMM input to PE) in series with the capacitance of the supply side to ground. This changes if you swap the DMM inputs.The long wires to the lab supply and the lab supply itself can introduce some RF noise and background to the capacitive ground loop. So things should be worse with the ref + connected to the negative input.

author: julian1
author_rank: Frequent Contributor
timestamp: February 28, 2017, 11:28:56 pm
content: What happens if you don't use twisted pair - is it worse?What about using ferrite beads/chokes on the leads going to the meter?For another data-point (ie maybe unrelated) I have/had significant emi issues with my ltz1000 - both breadboard and basic pcb implementations. I varied my design from the datasheet and used dual-rail op27 and not the ltc1006/13. I wondered if there might be something in the choice of op-amps - and if the r2r input/output stage of the lt op-amps might help supression.Things that somewhat helped (or reinforced the conclusion of emi) - was removing the signal diode on the output of the op-amp that ensures positive output for zener startup. I suspect it has some influence as an RF rectifier and added a varying output bias. Also, isolation in a metal can.

author: mimmus78
author_rank: Unknown
timestamp: March 01, 2017, 12:35:37 am
content: OK ... taken some more measurements and get still inconsistent results.Sometime things get better, sometimes sensibly worse.For example some days ago I checked reversed output with batteries and it was OK.Today I have drift and instability even with batteries, there should be something different I do that screw up.

author: mimmus78
author_rank: Unknown
timestamp: March 01, 2017, 10:23:25 am
content: GOTCHA!!!If I put battery pack on the antistatic mat with reversed connection I have the problem. If I move battery pack away no problem even with reversed connection.Generally anything that touch antistatic mat (included shielded leads) screw the things few ppm.This explain also why I had so inconsistent measurements during last two months.I already checked grounding of the mat (was 1M ohm), outlets and instruments and it was ok.I will do some more checks when I back to lab this evening.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2017, 04:57:51 pm
content: The diode at the output of the driving OP should add little more sensitivity to capacitive loading, but not much. At a DC current of about 5 mA the effective resistance of that diode is only about 5 ohms.The LT1013 does not have such an unusual input stage (only single supply, not rail-rail). If at all the low bias output stage could be a problem, but with the 5 mA of DC current it is working as a class A stage.One possible measure to improve EMI and load capacity tolerance might be an RC (e.g. 10-100 n and 100-220 Ohms) element to GND at the output. A ferrite bead could be a good idea too.The LTZ circuit from the DS is made for an instrument internal reference, not really to drive an external output and thus handle capacitive loading, possible ESD and RF noise. Also remember that to much load, so that the voltage drops well below 7 V would cause the heater to go for a higher temperature and this way possibly upset the reference and possibly even cause permanent damage if there is no sensible limit to the heater current.The OP27 and similar OPs have quite a high current noise and also bias drift and are thus not the best choice for a high source impedance (about the typical 70 K resistor).

author: mimmus78
author_rank: Unknown
timestamp: March 02, 2017, 12:23:14 am
content: Made some more tests and as far as I keep KX reference, his metal box and leads faraway from grounded mat I always get consistent measurements.My antistatic mat cover almost all workbench so it just happened some months laterthat I tested KX without any of this part touching it.With this precautions I can use different power supplies or different leads and get alwaysthe same output +/- 1uV.It even get's better if I use the Agilet e3641 power supply (instead of the Siglent). Output isidentical as with batteries and also reversed leads test produces the same and stable Vout.EMI also is now ok. With the buffer, some ferrite beads at Vin and at the "binding posts" andthe metallic enclosure seems to works reasonably well. The max drift I can producenow by using normal lab equipment and appliance is just 0.5uV.Still have to read/study what you all write back there to check if things can be improved toget also "mat" immunity.Anyway I'm starting to like where I'm going with it. I wonder what can be the experiencewith a 732a or 732b or any other serious stuff ...

author: julian1
author_rank: Frequent Contributor
timestamp: March 02, 2017, 06:40:48 am
content: Quote from: Kleinstein on March 01, 2017, 04:57:51 pmExcellent!. I bodged in a low-pass filter immediately after the diode R=100, C=100nF (I think that's a cutoff of 15kHz). Waving my hand over the unshielded board used to produce a 500uV output change. It's now very difficult to detect anything that could not be attributed to air circulation. The 12k/1k temp-set resistors are currently non-tempco ones so I'll wait to replace those before doing more tests. It really deserves a better pcb with gnd returns at this point.QuoteThe only capacitive load I am aware of is the multimeter probe tip/grabber and front-end circuitry.QuoteThanks, I followed your previous advice on this, and they were replaced with opa277.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 02, 2017, 04:04:45 pm
content: It only takes a few 100 pF at the output to upset the LT1013. The typical LTZ1000 circuit can be even more sensitive than the simple times 1 impedance follower. A DMM can have a significant input impedance, so is a certain length of wire. Even if not oscillating extra ringing from externally injected noise can cause trouble.The 100 Ohms and 100 nF not only function as a filter, they also represent a significant load to the OPs output and this way reduce the gain a little. This helps to improve stability at high frequency. Some amplifiers use this to stabilize the output with difficult loading.I remember an instrument (Lockin amplifier) which had just an OP to drive an output, that could not even tolerate an 2 m coax cable on that output.

author: mimmus78
author_rank: Unknown
timestamp: March 05, 2017, 12:31:18 am
content: So it's time to show you some data with this KX003.Reference (or 3458a) has drifted up 0.3ppm since first day but it's still stable.I run a 12h stability test, trying to keep temperature constant except my Daikin as a strange concept of constant temperature and it drifted 1°C in a day.Notice there is some drift due to temperature, this should be 50% due to KX TC and 50% due to 3458a TC.This KX seems it needs a 250K as compensating resistor ...

author: David Hess
author_rank: Super Contributor
timestamp: March 05, 2017, 04:01:54 am
content: Quote from: Kleinstein on March 02, 2017, 04:04:45 pmI never noticed the LT1013 being that sensitive to capacitive loading but at the end of Linear Technology application note 148 is a description of how to use an RC snubber on the output of an operational amplifier so that it can handle a capacitive load better; set R to the reactance of the load capacitance at resonance (measured) and the reactance of C to like 1/10th of that. If the load capacitance is poorly defined, then add a shunt capacitance to swamp it out.

author: mimmus78
author_rank: Unknown
timestamp: March 16, 2017, 10:55:42 pm
content: So today my KX reference gets one month old.Measurements drifted +1ppm in respect to my 3458a since day one.Also other two LTZ1000 references has drifted +1ppm in last week so I think this is most probably due to some hysteresis of my 3458a than the drift of the references itself.As bonus I enclose also here the noise floor of the KX reference + the buffer (thanks to Andreas for sharing the schematics, booth of the buffer and of his 10000x preamp).Considering my setup I think it's in spec with 1.2 to 1.4 uV p2p noise.

author: ap
author_rank: Frequent Contributor
timestamp: March 17, 2017, 10:03:38 am
content: Unless you have the 3458A running all the time (and even then) the 3458A is not good enough to verify a LTZ1000. I have seen that many times. That does not contradict 3458A spec, but even if you switch a 3458A of and on shortly thereafter, you see some hysteresis (at least if you have not reduced the LTZ internal temp.) There is no way arround a precise voltage reference...

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 17, 2017, 11:11:56 am
content: Quote from: ap on March 17, 2017, 10:03:38 amThat's not correct, the way, how you express it..Here, you compare two equally stable reference against each other.. one thing are the short /mid-term fluctuations, the relevant is the long-term timely drift.You can't decide with only 2 artefacts, which one drifts..."A" precise voltage reference (or better : "one" ..reference) is also not sufficient, even if you use a 732B, or similar, which is also equally stable than a LTZ1000 based reference.Only if you have 3 or more (equally stable) references, you may be able to measure the drift of one of its constituents.If you have even more references, and more of old, stabilized ones, the higher the probability is to discriminate drifty constituents of the whole group.The LTZ1000, and also the LTFLU inside the 732Bs in the median tend to drift about -0.8ppm/year, whereas the SZA263 in side the 732A and elder 732B, and also inside the 5440B tend to drift upwards, about +1ppm/yr.A mix of both types of references would allow better judgment.Then it's of course necessary to have regular re-calibration of that group.Frank

author: ap
author_rank: Frequent Contributor
timestamp: March 17, 2017, 02:36:43 pm
content: I dont think I said, and certainly did not mean it differently. Its in the end a question of measurement uncertainty of the gear you use, and its just too low in that case. Not the place going into multiple ref. type discussions here, anyone interested, e.g. Fluke explains it well in Calibration: Phil. in Practice. For Free: NASA cal handbook: Metrology — Calibration and Measurement Processes Guidelines.I do disagree with your one reference statement though; depending on established history, and time between CALs and so, even DAkkS allows that.

author: TiN
author_rank: Super Contributor
timestamp: March 20, 2017, 04:49:32 am
content: Received today KX LTZ module fromVK5RC. At least he was brave enough to take on my cross-check offer. Quick check show it's still working after a trip, so I'll add this guy for monitoring over next multiple weeks and run it thru temperature ramps. I think VK5RC has few weeks of data on it too, so it will be interesting to compare how our test results correlate. According to a label on the box, reference have Edwin's PWW resistors.

author: VK5RC
author_rank: Unknown
timestamp: March 20, 2017, 11:46:02 am
content: TiN; Thanks for the great offer!enut11 has been leading / encouraging a group of Australian V-nuts, one of whom has a recently purchased 7.5 digit Fluke. A set of mainly voltage references but also some resistors are doing the rounds in Australia.Just before the KX LTZ reference headed off - I did a quick temperature experiment - my lab heats up moderately on hot days (36C outside) - the temp inside going from 20 to 26C (my 3458 runs about 15-16C above ambient in general), the trace starts at 11AM heats up till 1320 (about 27C ambient) when I switched on a refrigerative air conditioner (AC) till 1500Hrs - dropping the temp to about 20C. Unfortunately I did not record differences coming from the temp sensor inside the KX LTZ but recall it was only a degree or so. I think most of the temperature change was inside the 3458A - it does have a fan after all!I use a Prologix (USB_GPIB) and RFScientific software (so far) importing into Excel- I am a Linux newbie. I am admiring the efforts of Tin, plesa and others in RaspPi and various GPIB pursuits!Below 1 Screenshot of Excel tables2 KX LTZ Unit prior to boxing - Rationale; I went with a vertical position of Mr Pettis' resistors to get their bodies close to each other thermally - I didn't use any copper tape (risk of short) - also the lead bending was a little more straight forward - the lead lengths are unequal though. The perspex lugs are only holding the board in place - it can move a mm or so but is touching some insulation foam inside its inner metal (diecast) box in an outer plastic box. The linear PSU for the 15V (TPS7A4901) is outside both of these.Again thanks to TiN and other EEVblog volt-nuts.Robert

author: TiN
author_rank: Super Contributor
timestamp: March 20, 2017, 12:53:51 pm
content: So that little bodge with 7805 is power supply for temp sensors?I got home, and hooked ref to a group already, but need modify code a bit as your ref connected directly at 3458B.Can you post your logs data as well?That green Teflon cable feels nice, I would mind knowing where to get some.Sent from my One using Tapatalk

author: mimmus78
author_rank: Unknown
timestamp: March 20, 2017, 01:41:39 pm
content: Yes I also wanted some of this cable ...Inviato dal mio Nexus 6P utilizzando Tapatalk

author: TiN
author_rank: Super Contributor
timestamp: March 20, 2017, 03:14:46 pm
content: Here's the thing:First samples:Quote from: 3458BPowered from K2400 (+11V, not 18V). Ambient is around 26°C.

author: SeanB
author_rank: Super Contributor
timestamp: March 20, 2017, 03:21:24 pm
content: Green cable is a standard PTFE insulated avionics shielded data cable, used in aircraft generally for either data buses or to connect low voltage sensors like thermocouples to points in the airframe. Makes a nice shielded cable, especially with the right solder sleeve shrinks to get the shield wire connection out.Also used as Audiophool grade interconnects, where they use the one core for signal and the other for ground, and only connect the shield to ground one end, or use it with XLR balanced connections.

author: sergioag
author_rank: Unknown
timestamp: March 21, 2017, 02:04:09 am
content: I have just finished my KX BoardIt has been powered like 4 hours now and attached are the pictures of the current measurement on my Keysight 34416A, as well as the board itself.I plan to have it powered up for about 1000 to 2000 hours so it settles down. Let's see how the voltage varies.In case you're wondering about the parts:- The Linear parts were bought from their web store.- The VPG resistors were ordered from UHP Resistors, which was referred to by Vishay themselves.- The rest of the parts were bought from Mouser.- The PCB was made by Seeed Studio. Too bad they can't put silkscreen over bare copper. Green was chosen as it was the cheapest and I had to save a few bucks back then (something I regret - red or black would've looked much better).I have soldered all the parts using my good old 30W soldering iron - no hot air station for me. The board is completely lead-free. I haven't soldered one of the Maxim ICs (the one on the front side) because I don't think I will be able to successfully solder it because of the surroundings.All the measurements are being made by my Keysight 34461A, which is about 120 days out of calibration. Hopefully I'll be calibrating it next month. I don't have a more precise meter.If anyone would like high resolution pictures of the board, please let me know and I'll bring the big camera for that

author: CalMachine
author_rank: Frequent Contributor
timestamp: March 21, 2017, 02:08:54 am
content: I wouldn't mind seeing some more pictures! I'm going to be making 2 boards myself here in the next few weeks.Also, something little I noticed.. Your DMM is in auto range. You want that bad boy on manual range

author: sergioag
author_rank: Unknown
timestamp: March 21, 2017, 04:26:17 am
content: Sure, I'll take some good pictures tomorrow.

author: TiN
author_rank: Super Contributor
timestamp: March 21, 2017, 04:26:35 am
content: Thumbs up for jumping in, we are always happy with newcomers.Green KX, yikesNo problems with that, now we need to get someone to make blue and white ones. I have red and black, mimmus has purple ones, you has green now.QuoteMost of fabs can do that, but you need to ask specifically. Reason why they don't put silkscreen over bare copper by default - is if you made mistake and put silk over pad, you will not be able to solder that pad.So they just being extra safe, nothing wrong with that.QuoteThis board does not need, and does not want hot air...QuoteI usually solder that one first, and only after put surrounding taller parts. Common rule for PCBA is to put small parts first, then taller ones, and connectors last.QuoteSure, show us your gigapixels.I'd be interested to see which VPG resistors you bought, what their cost was and how long you waited for them. I chose VHP202 70K ones only because there were no 70Kohm in Z202 small package.Also 34461A can do much better logging, set to manual 10V range, and reset statistics, so you can see variation down to 1uV AFAIK. I don't have 3446xA, otherwise I'd give you exact setupGood news forVK5RCreference, it's good and stable so far during overnight run, and here's initial chart (boldpurpleline):

author: Andreas
author_rank: Super Contributor
timestamp: March 21, 2017, 05:20:16 am
content: Quote from: CalMachine on March 21, 2017, 02:08:54 amAnd I think the more critical is the 10 Meg input impedance instead of being high Ohmic.with best regardsAndreas

author: VK5RC
author_rank: Unknown
timestamp: March 21, 2017, 08:31:19 am
content: Thanks TiN,You are right in that the little 'bodge board' is a DC PSU for the temp sensor ICs. The reason for the floating - 9V battery is I have some serious earth - loop issues. The temp sensor outputs are marked - one as REF (close to the LTZ) the other is the sensor close to the op amp.Thanks for posting the data - I am happy ! I am now pretty sure I know (approx) how far out, my out of cal 3458A is!I quite like the green cable but it is just a bit stiff - The conductors are quite thick - I have purchased two lots on eBay from.http://www.ebay.com.au/itm/10-feet-20-AWG-Shielded-Silver-Plated-PTFE-Wire-Green-Twisted-Pair-w-Drain-/232174685320?hash=item360eb08c88:g:YkwAAMXQrhdTQbWh- I would buy from him again.I will post my raw data later tonight but have to get it off another laptop.Robert

author: VK5RC
author_rank: Unknown
timestamp: March 21, 2017, 10:15:54 am
content: Below are the data combined of two of the longer runs, the first is the run with big changes in temperature in the Lab, and the second is an overnight with relatively stable temperatures. They were actually about 2 weeks apart, The KX LTZ reference was kept mostly powered up in between.Robert

author: TiN
author_rank: Super Contributor
timestamp: March 22, 2017, 12:03:47 am
content: Well, in that case you are+7.5ppmaway from me.Now we need 3rd person with <2ppm DC accuracy reference to jump in and save us.Anyone? Come out of the shadows...

author: mimmus78
author_rank: Unknown
timestamp: March 22, 2017, 12:20:31 am
content: Wish I could send mine ... but mine it's not shippable. After few power on/off 3458a is back to reading kx003 (and others two LTZ1000) as first day (+/- 0.2ppm).

author: sergioag
author_rank: Unknown
timestamp: March 22, 2017, 01:35:28 am
content: Here are the pictures I promised. Hopefully you enjoy them

author: VK5RC
author_rank: Unknown
timestamp: March 22, 2017, 01:46:00 am
content: I have no doubt my 3458a is incorrect, if I recall correctly last calibration was in Hong Kong about 7-10yrs ago (by Agilent no less) but another reference is always reassuring. The error of about 1ppm drift per year is not that unusual I believe.Robert

author: TiN
author_rank: Super Contributor
timestamp: March 22, 2017, 04:09:02 am
content: Quote from: sergioag on March 22, 2017, 01:35:28 amThose are small pics.There are is alarming item though - R3 must be 12.5-15Kohm , not 10Kohm, unless you plan to run your LTZ in freezer all the time.10Kohm is way too low for temperature setpoint for reference used in ambient.Also it's better to clean flux residues to prevent gotcha's.Your Z202 resistors look also very interesting as well, not usual marking font/typeface found on VPG resistors.

author: sergioag
author_rank: Unknown
timestamp: March 22, 2017, 04:31:11 am
content: Quote from: TiN on March 22, 2017, 04:09:02 amI wanted to upload something larger, but the forum will only accept up to 1000kb per file, for a total of 2000kb... and originals in RAW are ~50MB eachQuote from: TiN on March 22, 2017, 04:09:02 amYou mean R5, right? (R3 is 120 Ohm) In that case, I'll order both P/N Y107312K5000T and Y107315K0000T just to be sure. And maybe even Y107313K0000T (as seen in Linear's reference schematic). Taking into account that here the temperature is usually around 18 C on Winter and 25 C on Summer, would you make any recommendation?Quote from: TiN on March 22, 2017, 04:09:02 amYes. I still have work to do regarding cleaning. Even further, when taking the pictures I also found a flux bubble below the LTZ can. I tried to take a picture of it, but it didn't really show.Quote from: TiN on March 22, 2017, 04:09:02 amWould this be something to worry about? I bought them from UHP Resistors, which was referred to me by Vishay themselves. Perhaps a newer batch or something like that?Thanks!

author: branadic
author_rank: Super Contributor
timestamp: March 22, 2017, 08:05:58 am
content: Sorry, but I can't resist. The solder joints are looking very very poor. Most pictures of hobby electronics injure my eyes everyday, so I need to make this statement.As reliabability of a circuit is within the interconnections of the components in particular the solder joints you want them to be "as perfect as possible". Otherwise thermomechanical stress will lead to micro cracks within the solder joints and furthermore to failure.Design and fabrication of reliabable circuits and sensors is my everyday job and assembling technology is the major key to meet this requirements. So my request is to improve your soldering skills to guarentee that this expensive components are working fine for a very long time. Even if you think about shipping this reference all over the place it should be your goal that everything works just as it should. Better use non-RoHS conform solder instead of gluing things together with RoHS conform solder, please. You have spent a big buck in those parts, so don't make any compromise in the end by a poor aseembling. Thanks.branadic

author: sergioag
author_rank: Unknown
timestamp: March 24, 2017, 01:40:11 am
content: Yes, I know...It's not quite good... I'm just transitioning to lead-free solder and thought it would be a good idea to try there - obviously it wasn't. Add that to the fact that I'm just using SMD components for about a year.Anyway, I've already ordered the VPG resistors for 3 more sets. Lead time has been quoted as "about 17 weeks" so it'll be a while. In any case, those 3 will have regular leaded solder, the one I'm familiar with.As for this set, I'll try to resolder some parts with leaded solder, but I'm afraid about ruining the foil resistors and the LTZ can. Let's see how it goes. Of course I'll post new pictures after that. They won't be as pretty as the next ones I'll build, but hopefully better than my last pictures.Sergio

author: plesa
author_rank: Frequent Contributor
timestamp: March 24, 2017, 08:17:02 am
content: For next assembly keep the wires on foil resistors longer and cool them with tweezers at least.For your LTZ1000A the R5 should be >=13k too keep temperature margin.R5 and R4 creates divider to set temperature, so you can increase R5 or decrease R4.Also before next reference assembly train soldering on cheaper componentsSorry

author: VK5RC
author_rank: Unknown
timestamp: March 25, 2017, 09:06:33 am
content: I love the solder (leaded of course) with just a little bit of Silver, a percent or so - seems to flow much better - I used .3mm when building my LTZs. I managed to make a solder bridge on two occasions due to the closeness of the guard trace (and my shake!!!) . Found before power on fortunately.

author: TiN
author_rank: Super Contributor
timestamp: April 01, 2017, 06:29:44 am
content: You guys make me work... Received KX B03 PCB fromSvanGool. Looks quite nice, and substrate is lighter color, which is usually for higher Tg substrates. I'd expect these boards are bit more pricey than mine.Couldn't resist putting few caps already before taking photos, sorry. Now the "problem" is that I'm out of LTZ chips, so might just order one, likely ACH-version.Also this one will have Edwin's PWW resistors, as all my others are with BMF/MF.Are you excited? Which opamp shall I use, ADA4522-1 or usual LTC2057?(yes, LT1013 is enough, but that's not the point)

author: Kleinstein
author_rank: Super Contributor
timestamp: April 01, 2017, 07:03:16 am
content: The LT1013 is not only good enough, it is about the best suited OP available. There is a very similar version from Ti (OPA2234). If there is a negative supply available (or in the negative voltage circuit) there are a few more choices.The problem with AZ OPs is, that they are usually more sensitive to EMI and also produce EMI. So I see no good reason to choose an AZ OP in a circuit that really don't need it. An AZ OP can be a good choice for a stage behind the reference, e.g. amplification to 10 V.If one would really like to go beyond the standard circuit, the more obvious modifications are not different OPs, but more like better RF tolerance and maybe a linearized and power limited heater circuit or even a second layer of temperature stabilization. A different OP might be needed if for some reason a lower noise in the 10-100 kHz frequency range is needed - but this would not be an AZ OP.

author: Andreas
author_rank: Super Contributor
timestamp: April 01, 2017, 07:11:18 am
content: Hello Illya,try the ADA4522 then we will have an option when AD drops the LTC2057On the other side: the ADA4522 seems to have a capacitive load problem (stable up to 250 pF)So perhaps that is not the best option (together with the lower open loop gain).with best regardsAndreas

author: TiN
author_rank: Super Contributor
timestamp: April 01, 2017, 07:49:40 am
content: Perhaps I've used wrong word regarding 1013. The board design use single-amp package only, so 1013 is not a direct option here.Indeed if one need proven design, there is no reason to go for anything other than 1013, which is what we see in almost every commercial device with LTZ1000 ref.ADA4522 was already used in module built at very beginning of this thread. No visible difference from other 2057 or A9 3458A ref in terms of tempco or output noise, based on limited testing.

author: David Hess
author_rank: Super Contributor
timestamp: April 01, 2017, 11:01:22 am
content: Quote from: TiN on April 01, 2017, 07:49:40 amThe LT1006 is a single LT1013/LT1014 but has offset null and programmable supply current for low power or high speed (low noise) operation.I forgot; what makes the LT1013 uniquely useful in this design?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 01, 2017, 11:32:50 am
content: The LT1013 is a precision single supply OP with about the right balance of input bias / current noise and voltage noise.Single supply is convenient as the common mode voltage is about 0.5 V in the positive ref circuit.Voltage drift and low frequency noise is not that important, as the transistor in the LTZ1000 already provides a gain of about 200. The source impedance seen by the OP is a little below 70 K (of whatever resistors are used to set the transistor current).There are a few rather similar alternative, like OPAx234 or maybe even OPAx171.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 01, 2017, 12:40:25 pm
content: Quote from: Kleinstein on April 01, 2017, 11:32:50 amDefinitely not the OPAx234, as its common mode range doesn't include the negative supply. The OPAx140 may work rather well though.CheersAlex

author: TiN
author_rank: Super Contributor
timestamp: April 01, 2017, 05:15:55 pm
content: Assembled the board.But likely got LTZ's temperature sense transistor killed by ESD.Dropped chip on the floor by accident. Now heater section does not work, pin 8 stuck at 0.11V and output is +7.50x V. Removed chip, moved on my other module with socket, same stuff.Moral of the story : don't drop your LTZ's and wear ESD-protection.Now need to get a replacement. Digikey will be happy (need to get some other parts, so i'll just drop in fresh chip there).

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 01, 2017, 06:20:28 pm
content: At least you didn't do it live with witnesses like someone I know hooked up battery terminals backwards while a friend was watching remotely.

author: Andreas
author_rank: Super Contributor
timestamp: April 01, 2017, 06:42:30 pm
content: Quote from: TiN on April 01, 2017, 05:15:55 pmShure you didnt kill the resistors?(bending the wires without strain relief directly at the case).With best regardsAndreas

author: Cerebus
author_rank: Super Contributor
timestamp: April 01, 2017, 07:05:37 pm
content: Quote from: ManateeMafia on April 01, 2017, 06:20:28 pmI've done that often enough that breadboards and circuit boards that are likely to be 'messed about with on the bench' get reverse biased 1N4007's or similar slapped across the supply rails on the board before I do anything else. It doesn't help that my favourite bench PSU (favourite because it's fan free and also electrically quiet) only has a fixed current limit.

author: plesa
author_rank: Frequent Contributor
timestamp: April 01, 2017, 07:14:32 pm
content: Quote from: Andreas on April 01, 2017, 06:42:30 pmwhat me worry is long term stability because of stress in bobbin.

author: mimmus78
author_rank: Unknown
timestamp: April 01, 2017, 07:20:26 pm
content: Quote from: ManateeMafia on April 01, 2017, 06:20:28 pmMostly is bad luck.I tortured one of my ltz reference badly.Hocked power supply backwards on my fist KX reference build because Siglent and Agilent power supplies have swapped positive and negative binding posts.Than I soldered backwards because I had used "mirrored" footprint on my design.Soldered/desoldered it something like 10 times when testing many KX and my design.You won't believe me if I tell you is still working and stable. It's just a little bit noisier than normal, mostly cured by using 100 ohm resistor instead of 120.Inviato dal mio Nexus 6P utilizzando Tapatalk

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 02, 2017, 06:03:42 pm
content: TiN <respectfully, suggestions just based on long experience>:For all the time, money and effort you're going to, I'd just order some new resistors directly from Edwin. When you re-install, -don't- kink the leads against the resistor body like you've done. Not only does that create brand-new unstable resistors in the leads where you've cold-worked the alloy and strained it with high compression and tension zones, but that can also literally jack-pull the lead out of the body internally - which can tug on the weld point. In some cases you also destroy the resistor lead's ability to carry thermal heat flow in and out of the resistor wire - which in a PWW is where a lot of the heat flow must to take place if you want stability.Otherwise any tests you do from now on are just checking damaged resistors, not known good production quality PWW's.In our lab if we saw a precision resistor mis-handled like that it would immediately be rejected & tossed - just too many potential problems later on. Only use a gentle lead bend radius when assembling and never expose the body to lead stress - be it mechanical or high heat. Better yet: use a proper lead former jig, and follow good minimum bend radius specs (min radius is at least 4x lead wire dia or more) and as Andreas pointed out you want length of untouched exposed lead at each end of the body as strain relief. We use a heat sink properly when assembling -any- precision resistor, whatever type.If possible, for a more accurate test use the correct PC board layout pad spacing to accommodate the resistors also. Precision circuits call for good power in / power out stability, and that means stable heat flow.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 02, 2017, 07:05:37 pm
content: @MisterDiodesWould you recommend a simple bend or one that includes a strain relief bend in the leads?I have looked at some of the tools available but I cannot decide if it is worth the added expense. Personally, the simple plastic lead forming tools would be adequate for me. As long as I get repeatable bends I can make the right component in my CAD software.

author: ap
author_rank: Frequent Contributor
timestamp: April 02, 2017, 07:21:43 pm
content: You could use standard tools, just make sure when the leads are bent, the bend is between two tools (not a tool applying force on one side of the bend, and the resistor body being to other part that applies a force to that wire bend area, because then stress is applied to the resistor body).As always, good workmanship re. parts preparation (as well as soldering...) is specified in NASA/ESA or MIL documents.

author: Cerebus
author_rank: Super Contributor
timestamp: April 02, 2017, 09:22:51 pm
content: If you don't have a purpose designed lead forming tool to hand may I recommend the use of locking surgical forceps (also known as haemostats) for bending leads and for soldering. Such as these:They let you get a very positive grip on a lead without damaging it (they are designed to clamp arteries without damage) and you can bend it without transmitting any force to the component body. Use one pair to hold the lead and another as an anvil to get a nice radius in the bend.In my experience they make much better soldering heatsinks than most of the purpose designed tools. They are also great for picking up that tiny screw you just dropped into the depths of a chassis while reassembling something.They come in a range of sizes and, best of all, they are cheap, you can pick up a set of 4 on flea-bay for under £2 each. It's one of those tools that, once you have some, you'll wonder how you lived without them all these years.

author: VK5RC
author_rank: Unknown
timestamp: April 03, 2017, 05:51:20 am
content: +1 re forceps - that is what I used in forming the leads of the 'good' resistors of the LTZ KZ reference - pictures in reply no 257 of this thread - I also used them as a heat sink when soldering the resistors and the LTZ to reduce heat stress - but with the LTZ I think you may replace the heat stress with a mechanical one. You also end up with the LTZ 4mm or so above the PCB. Swings and roundabouts.

author: Cerebus
author_rank: Super Contributor
timestamp: April 03, 2017, 05:20:08 pm
content: Quote from: VK5RC on April 03, 2017, 05:51:20 amThe various types of forceps have names, the commonest one you'll find are called Kelly forceps. Mosquito forceps have, as you might expect, narrower jaws and are a better option if you're concerned about introducing a standoff between a device and board when using them as soldering heatsinks.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 04, 2017, 05:25:38 pm
content: Quote from: ManateeMafia on April 02, 2017, 07:05:37 pmGenerally as few bends as possible, but don't over-kink the leads. We define a kink here as any curve with a radius < 2X wire diameter - that can really inhibit heat flow. Keep the bends as gentle as will fit your application.We use an in-house built jig that forms several components at once and acts as an assembly heat-sink, but there are commercial adjustable component formers that are required for military / aerospace / medical use - and for prototypes we also have some good round-nose pliers we can use as a lead bend former (dia around 0.200").A well-equipped assembly contractor will have a thru-hole board stuffer / prepper with a handling head that puts on a smooth adjustable-radius bend to your precision components - you specify the pad spacing and minimum allowed curve radius, and they handle the rest. Sometime they will build a component former block that fits into the machine custom-made for your project.The plastic lead former tools are better than nothing, and can work well if you're careful but those can make an over-sharp corner on larger lead wire. You might have to modify the cheap lead former so that it puts on a larger-radius curve.The general idea is when you bend the component lead, keep all stress away from the resistor body - so that means you really want to grab the lead in two places and guide it around the former corner - don't make the resistor body take any bending stresses, and don't extrude or cold-form the lead as it goes around the corner.Don't let the soldering heat get directly into the body either - if that epoxy or body softens you can get into trouble and ruin a good component. Keep the soldering time short and precise - and make use of a heat sink. Even some stainless steel wool, de-solder braid, coax braid, etc. held against the component lead while soldering can act as an emergency heat sink if you don't have a clip-on style.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 04, 2017, 08:13:25 pm
content: Thanks to everyone for their suggestions.It seems all details cannot be ignored when working at the ppm level.

author: TheSteve
author_rank: Unknown
timestamp: April 05, 2017, 04:19:55 am
content: SvanGool was kind enough to send me a PCB so I am joining the club.I plan to build it using resistors sourced off of ebay. This does limit the values I can acquire a little bit. I will be using 12.5K for R5 and am wondering if people recommend keeping R4 at 1K or would 900 ohms be better to run the LTZ1000A a little hotter?

author: TiN
author_rank: Super Contributor
timestamp: April 05, 2017, 04:49:02 am
content: That really depends on your max ambient. Hotter gives you little higher long-term drift rate in theory, but in practice you wouldn't be able to measure, unless you has banks of 732A/B.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 06, 2017, 12:57:09 am
content: Quote from: TheSteve on April 05, 2017, 04:19:55 am12.5k at the very low end (based on experience), if your ambient is pretty much always on the cooler side. You'll have to see how your board works in your enclosure, insulation, etc. We use recommended 13k as lowest value, but on a warmer production line situation we'll go with 14k~15k, as used by HP in 3458a meters.If your circuit is running too cool it will stop being stable at higher ambient temperatures. You need that LTZ to be above ambient (ambient temp around the LTZ) at all times so it can stay at a stable point...It only has an on chip heater, not a cooler.TiN is correct: The change in drift rate at higher temps is not significant for a hobbyist to worry about and unless you have several 732a/b's to compare against. And maybe not even then. The bigger contributor to overall drift rate will be your unique LTZ die and the luck of the draw - beyond your control. It is not uncommon to see LTZ's that really don't have much measurable change in drift rate at higher temps... but some are more sensitive of course.I can also point out several 3458a's that we've used that run at their standard 15k / 1k that don't drift a ppm / year, if that makes you feel any better. They are perfectly happy at that heater ratio, and have been running for decades that way.I'd assemble your circuit, fire it up, get it in your enclosure and let it run a while - and then you can test what effect ambient temp has on -your- circuit situation. Let it run several months to settle in and establish a reference baseline. LTZ circuits take some patience to really study and if you've done it right it's really about the best reference you can build without a government-sized budget.

author: Andreas
author_rank: Super Contributor
timestamp: April 06, 2017, 06:53:29 pm
content: Hello Steve,with 12K5/1K the nominal setpoint will be around 52 deg C nominal (+/-10 deg Tolerance).I built all my 6 LTZ1000A with 12K5/1K (0.1% or 0.01%).All are tested to environment temperature up to around 40 deg C. (38 deg C in the linked picture)So for a maximum room temperature of 32 deg C I will be on the safe side.( If I do not place the reference on a very hot calibrator. )https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg928435/#msg928435With best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: April 06, 2017, 07:16:38 pm
content: It also depends on the thermal setup and zener current how much self-heating will rise the temperature above ambient. Especially with the A version, the self heating can be important - this is why it needs the higher set temperature. Working very close to the temperature limit also means low heater power.Due to the resistive heater with a square law for heating power, the heater control loop will see a lower gain at low power. So a low heater power might want a slightly modified (e.g. more gain at low power) temperature control circuit to get the same level of temperature control as with higher set temperature. With the original circuit temperature control will be not as good close to the limit.Of cause the is no problem using a slightly lower resistance for the divider.

author: TheSteve
author_rank: Unknown
timestamp: April 07, 2017, 06:59:27 am
content: Thank you for the advice guys. I'll probably stick with 12.5K/1K - my shop is generally quite cool.

author: TiN
author_rank: Super Contributor
timestamp: April 16, 2017, 05:27:59 pm
content: VK5RC's KX tempco test ramp finally complete.I had to replace diecast box to twice bigger one, to fit his reference with it's box, to keep it as it was received. Still had to crook input LDO box on the top to have it all fit.Concept is same, 50W TEC is attached on the bottom side of the box, cooled by CPU fansink. Whole thing controlled from K2510 in PID loop.Feedback RTD, which is Honeywell HEL-705 Pt1000 jammed right against reference's inner metal box. Due to this I had to really crank gain of PID and make everything very slow, about 0.005C/minute otherwise whole loop oscillate like mad.Reference's LDO power input was powered from K2400 SMU, set at +18.000VDC, 105mA compliance. Current consumption was around 15mA at +40C TEC BOX temp, and about 20.6mA at +22C. My KX reference design have two temperature sensors on PCB, which are MAX6610. One is near zener's opamp, second one is on bottom side next to LTZ. I've used handy K2002's to monitor temperature sensors. They were powered by 7805, which is in turn powered from 12V SLA. Due to long time I had to charge SLA from K2304 from time to time.LTZ's output directly monitored by 3458A. ACAL DCV performed automatically on each 0.2C of ambient temperature change. Otherwise tempco of my meter is about 0.28ppm/K, so it was being corrected out.Overall setup look:And data graph plot. Blue and purple line are MAX6610 outputs, and one can clearly see how LTZ's oven temperature regulation reaching less and less margin, as temperature of far PCB end getting closer to center spot.Final tempco of this run as result =-0.14 ppm/K ±0.02 ppm/K, which is quite bad for typical LTZ1000, to be honest.

author: Andreas
author_rank: Super Contributor
timestamp: April 16, 2017, 08:47:29 pm
content: Hello Illya,a negative T.C. can be healed by either shortening the legs of LTZ1000A or by putting a (smaller 220-270K) R9 resistor.with best regardsAndreas

author: TiN
author_rank: Super Contributor
timestamp: April 17, 2017, 12:35:14 am
content: There is nothing left to shorten on the chip, also you mean 400K R9? Afair, it's not on the module. However it can be added.Let's hear from the owner, what he want to do.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 17, 2017, 12:58:46 am
content: Quote from: TiN on April 17, 2017, 12:35:14 amTiN: Are you running 12k over 1k for heater resistor? That might be a little cool for your setup - being all sealed up in boxes, etc. watch your heat flow away from LTZ - it can't be zero - your heater could be running out of operating headroom for that LTZ. I wasn't sure if you've got a thermocouple on the LTZ itself.There is something wrong there - that TC is much higher than what we've seen with PWW, both Edwin's and GR's - and Films. It's usually closer to Datasheet TC value with recommend 13k / 1k to start...and then work to a lower value as your setup permits.Do you have the new heater ratio resistors properly mounted on the PCB this time (not mangled like pictures before, sorry), and thermally close together? I guess I didn't see the LTZ board itself, or I'm blind.Have you done several thermal cycles? Is this a brand-new LTZ or one you've used before?Why the '2057 instead of recommended LT1013? Not that it causes that high TC, just curious. LT specifically recommends against the '2057 for it's high current noise across the LTZ - it can be a source of instability long-term. We -never- use AZ amps for these LTZ current drivers.You might want to run the test circuit as the standard, recommended setup. That's what gives us lowest TC and best stability, time and time again - at least we haven't seen one with this high apparent TC. Usually its much closer to datasheet specs or better, at least that's our experience.You might run a few more cycles and see if there's any indication of settling down??

author: TiN
author_rank: Super Contributor
timestamp: April 17, 2017, 04:03:11 am
content: That's a good lot of questions, great!QuoteThat's right, 12K/1K. Previous test reveal that oven runs out of margin bit over +42°C, so as result TC ramp goes only to 40°C. It's very clear when there is no headroom left, by obvious +42ppm/K zener TC.QuoteI agree with this. However it's not mine, so owner has to decide if he wants surgery. I can try one minor thing, but that will be next week as gear runtime required for other stuff now. The original idea of me checking VK5RC's ref was just calibration test/comparison. But I feel of providing single data point, even median without knowing tempco is half-ass job, so much longer testrun is done as result.QuoteSorry for bit of confusion, you are not blind. Mangled board (no offence taken, it's true) is my test module, which is waiting for LTZ chip now, so it's not the same ref. VK5RC posted photo of his modulehere.QuoteYes, it had about of week of cycles prior to the ramp on post above. It was aged for a month at VK5RC site in Australia, then he shipped it to me for tests and it was compared vs my other 5 LTZs for another ~300 hours, before any temperature cycles even start.QuoteLong story short - it's by historical reasons. By that I mean my first volt-nuttery entrance3 years ago, when I've designed KX PCBA, which takes two single-opamp SO8 packages for the LTZ circuit. Back then I had less understanding about opamps, their performance measures, etc. So PCB physically incapable taking LT1013 without doing bodgewires. And it was not expected that anyone order my gerbers or make modules, but here we are. I'd design things bit different today, having negative supply rail, larger footprint to support multiple options for precision resistors, not just tiny Z202's, use LT1013, provision larger capacitor footprints for films...QuoteI'm not going to argue on this, valid points. Just so far on hobby level I doubt difference between 2057 or 1013 or other opamps can be distingueshed with equipment we have available, be it 3458A or null-meters and 732B, looking at the output. I have 4 my modules with LTC2057, one with LT1097 and unmodified HP3458A's A9 STD REF module, which I compare from time to time over last few years. I was not able to tell the difference from data in short-term noise on any of them without actually looking at the board.QuoteYep, but that would mean making new design, new boards, ordering another boatload of expensive parts and spending another year on testing everything. With likely the very similar unmeasurable difference outcome, as down to ppm level there are so many things that can go wrong. At this point in my life, I'd rather spend efforts on few other projects. Perhaps new wave of LTZ-nuts would be willing to try this road, so we can see more different and interesting designs here.QuoteHaving reference return to original voltage after ramp down suggest not settle/unstability issue? If it's unstable, we would see different end voltage. Power cycle for 30 minutes (moving VK5RC's REF from TEC box to near LTZ bank and K7168 scanner, reference voltagerestored to -0.4 ppmof original assigned value, including 50% error from different 3458A.Attachedfull loggraph, with rescaled ppm scale at +140/-2ppm. Clearly can see when oven failed to stabilize die temperature around 6pm April 10. Rest of the crazy stuff I was tuning PID for TEC controller before I got right magic and started test April 13.

author: Andreas
author_rank: Super Contributor
timestamp: April 17, 2017, 06:48:15 am
content: Quote from: TiN on April 17, 2017, 12:35:14 amHello Illya,yes I mean the 400K resistor which is populated as R9 on my cirquit.As a rule of thumb I calculate a 1 Meg resistor to compensate for -0.04 ppm/K.Quote from: MisterDiodes on April 17, 2017, 12:58:46 amThe 2057 has nothing to do with a bad T.C. My worst sample with -0.23 ppm/K uncompensated T.C. (LTZ#4) is built with a LT1013A.Both 2057 samples have below 0.03 ppm/K T.C.Do you have a application note or a serious source where LT recommends against the 2057?Only notorious repeating without founded measurement data doesnt make it plausible to me.with best regardsAndreas

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 17, 2017, 04:27:05 pm
content: Andreas:Call LT analog apps engineering - compared to a '1013, that '2057 will have somewhere between 200 to 400 times current input noise as spikes on the inputs, @ switching freq - and noise probably won't show up on the output due to a low speed amp, but will really show up on the inputs and power rails.ON AZ amps: EVERY time the input pins switcher FETs change polarity, there is an injected gate charge current onto those inputs -That injected gate charge has to go to/ come from somewhere, and the only route open to it is to flow on the input pins, while even more charge has to be drawn from power rails. That's the dirty little secret of all A-Z amps. Yes the output won't show noise at switcher freq, but you'll find it everywhere else around the amp...be warned. All A-Z datasheets will tend to gloss over this problem...AD has some A-Z amps with dithered switcher freq at least, and so they admit to the problem since they are trying to address it.Look for short, tall input current spikes on '2057 inputs, at around 100kHz. Also on power rails. They can be in the uA (peak) range, and they are not included in the other noise specs at all. The datasheet does briefly mention 0.7nA RMS input current noise at 100kHz...but that's not the story on current PEAKS: which are short and tall.NOTE: This effect is NOT modeled at all on LT-Spice. In fact the switcher noise isn't modeled correctly for most of their AZ amps, '1043, etc.That's not something LT measures for their datasheet, nor do they talk about it on their datasheet. So measure for yourself - I have posted links to the measurement techniques here before, and you can see that effect for yourself - you don't have to find it in print or listen to me. We have done those tests, but at client's expense and is not public - otherwise I'd be happy to show you our data. Also, LT has confirmed to me that '2057 input noise spikes are certainly not the quietest for among common AZ amps either...but for some applications (resistor bridge input buffer) maybe the effect can be ignored. Not so for LTZ, where the noise spike current is injected right onto the LTZ die - which you don't ever want. Why would you choose to generate -more- noise across the zener and reduce LTZ stability for no real final benefit?Will a '2057 work? Sure. Any better than '1013? Nope. So go with the much lower noise, recommend solution. You have not invented any better wheel with a '2057 in this application.For that reason, LT really doesn't want anything but LT1013 as the best op-amp to pair up to LTZ. It really is the best middle-of the road compromise between input current noise vs. voltage noise. If you get an amp with low voltage noise you'll get high input current noise, and low current noise amps will have high voltage noise, etc. Always a compromise. '1013 sits right in that middle sweet spot, and that's why it's the amp that is the perfect fit for LTZ.Oh - If you want to read more about it, check the Art of Electronics, 3rd edition (Horowitz & Hill), where you can find theory for you to learn more about A-Z amp noise. Look in the chapters about Op-Amps, and Precision Amp circuits etc. I think around chapter 8 - maybe. I don't have page numbers for you but I know it's there - in fact the current input noise range they quote will be say 400 times that of a non-AZ amp...but our tests weren't quite that high, but in that ballpark. The authors ran tests also, if you don't want to believe me. Or just test for yourself.Once you learn about input current and rail noise noise, those AZ amps used for LTZ current drivers aren't all as rosy as they seem, especially for long term stability. They have their place for sure, but not as an LTZ current driver.Can '2057 be used as a low drift voltage boost amp / buffer? Maybe. But again, watch out for those danged AZ switching spikes that get everywhere else if you're not ready for it. We're working on a 24 bit fast ADC now, and at those high resolutions ...boy, it gets very tough to keep the noise down in the mud. It is sometimes more forgiving if you have a radiometric input for your hi-rez ADC, but this one isn't and needs a very quiet absolute Vref - so low noise is critical. It turns out that a '2057 isn't the best choice for that either - watch out for very low drive current from these AZ amps, and adding an LT1010 isn't always the best either. Traps everywhere at high bit counts!!Here's that link I posted before on a chopper noise measurement technique - with some modifications this strategy can be used to explore '2057 noise and compare to other AZ amps. Have to use shielded can. '2057 will not have lowest or loudest input noise compared to amps described here, but it's up there:https://e2e.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-14-01-00-00-70-21-03/Chopper-Noise.pdf

author: TiN
author_rank: Super Contributor
timestamp: April 17, 2017, 05:00:44 pm
content: Since you mentioned fast hi-res ADC, you got me here though. Chopper amp definitely have source to generate extra noise, but LT still recommend using 2057 as input buffer if near DC signal need to be digitized accurately for new generation of their 32-bit SAR ADC, such as LTC2508-32. What would be better solution for DC accurate preamp for such ADC frontend/reference buffer, to digitize low signal levels in 0.1-1kHz band (e.g. as servo system for DAC).Also 2057 datasheet covers charge injection a little, having DC average current included in bias specification.

author: branadic
author_rank: Super Contributor
timestamp: April 17, 2017, 05:32:17 pm
content: @ MisterDiodesAnd what is your recommandation and experience on LT1013, which one would you use:- hermetic LT1013AMJG which is e.g. still available at RS Components made by Texas Instruments (http://de.rs-online.com/web/p/operationsverstarker/7320847/)- one of the original available Linear Technology LT1013AC/LT1013C/LT1013D/LT1013I- DIP (CERDIP) or SO8?- if DIP (CERDIP) with or without precision sockets?

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 17, 2017, 05:38:50 pm
content: Andreas:Info in print for you - this way you don't have to believe me, and a good discussion of the theory of what's happening. Make sure you have a copy of Art of Electronics, 3rd edition at hand.Go to page 337 and you will see an example of an AZ amp noise measured at 400X the datasheet value, and look how much higher that is compared to a low current noise bipolar amp.Check section 5.8 thru 5.11 for a pretty thorough discussion on A-Z amps and various problems (especially current input noise spikes) and watch out what happens if output saturates.You will find some real spectra plots of current input noise that run all the way up to the switcher freq and above - something you don't really see on A-Z amp datasheets. '2057 is mentioned in text in a few places but it is the similar design as other LT choppers listed.Also check 8.9 and beyond.After that, test your own - Input current noise density typically WON'T be on the amp datasheets, or - like LT - they just gloss over it and mention an RMS value, which completely hides the fact that the noise is in the form of a short, big spike.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 17, 2017, 06:02:19 pm
content: Quote from: branadic on April 17, 2017, 05:32:17 pmWe've had good luck with plastic DIP as is done in 3458a. If you really want a metal can, they do have those from time to time at LT's site - around $48 each. We've never seen any cost-benefit from those, but whatever your spec calls for.From what we've done, regular DIP seems to have less problems mechanically and from vibration pickup, and solder straight to board - no sockets. If you're worried about very small humidity effects, go for a hermetic box with a nitrogen or C02 purge valve, or semi-sealed box with silica pack, or vacuum deposition coating. Only if customer desires those features though. The cost to go that route just to chase down a small fractional ppm is very high.Normally we don't worry about just using just a plastic DIP pak in a protective (emi and air draft) enclosure, and protect the LTZ itself from air drafts - just like HP has always done in 3458a and all seems to be fine for most any use on a production line situation. Our products do go through periodic cal and adjustment, and are normally within spec.We have used PWW resistors from G.R., Pettis, Riedon, Vishay and all work well with LTZ - Sometimes customers really want hermetic film and we'll do that also, but no real improvement in Vref operation cost per ppm stability. If you're temp range is small enough PTF56's work on the cheap <Laughing> ..but at the cost of LTZ you might as well use good resistors. For DC work PWW work well and cost is very reasonable compared to expensive film units, plus you get the exact values you want - but if you have a place where lots of high freq noise around you might have to use better box shielding or film resistors to reduce pickup.Just depends on what you're going after. If you're chasing absolute lowest possible 1/f noise effects down to DC, then PWW resistors are where it's at.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 17, 2017, 06:47:12 pm
content: Quote from: TiN on April 17, 2017, 05:00:44 pmTiN:That's funny you mentioned 2508-32, and I was JUST on the phone with LT. I have to tred very lightly here on public forum, and I was asking them the same questions about Vref noise / '2057, etc. I am under NDA with LT since we do some work for them BUT:1) The 2508-32 is NOT a -true- 32 bit ADC, as they are quick to point out. It has 32 bits max -resolution- with all filters turned on and only at max decimation rate, but that is NOT 32 bits true DC resolution. This is NOT a poor man's 3458a voltmeter. If your input signal or Vref noise is not Guassian, forget it - those SINC / Averaging filters won't help you at all.2) They will discuss techniques trying to use a 6655 as Vref source, but putting a multi-stage '2057 LP filter at 0.8hz, and then you still need a buffer to buffer / drive Vref input on the 2508. Which still leaves 1/F noise problems. The only trouble is that only gives you a realistic measurement time span of some minutes, not even a 10 minute's worth of stability for repeatable measures. OOps. where did that 100kHz show up from?? Ooops...that '2057 is getting noise into the Vref driver buffer. Ooops...maybe a Bipolar buffer amp is better... Maybe we deal with a little bit of drift somehow.OOPS - don't let that '2057 saturate in the filter, or it'll take some time to recover....Ooops...when it recovers it's got a little hysteresis... and so on.I'm not saying '2057's are bad, but these are really tough problems in general at high bit counts. Every bit of noise becomes a problem.3) The clue on these ADC chips with very high sample rates (1MHz) and associated noisedon'tmake them the best choice for an absolute DMM-style voltage measure device. These are generally more for weigh scale / pressure transducer / seismic transducer where your sensor is typically a resistor bridge and driven by the same Vref the ADC is running from - so your input signal is always a RATIO of Vref. That way your Vref can wander around a little bit and you've still got some fairly decent signal data.All in all that 2500 / 2508 are probably good 16~18 bits chips if you need faster sample speed, but be careful: Notice that the SNR and distortion aren't even good for 20 bits or so even at lower freqs?Still faster than a 2400 / 2408 BUT one thing with those chips is the 4ppm INL is fairly predictable and curves trimmed out in software. The 25xx. chips have lower INL but not as trimmable.Yeup: That still exposes the elephant in the room with Vrefs: For stable absolute measures down into the sub-20~22bit range, you have to have a quieter and quieter Vref and NO 1/f noise (or as low as possible) if you want to make repeatable measures over longer time spans. This is at the point where even LTZ's and 732a's aren't going to be good enough for a true, quiet 24 bits flicker-free at DC. That ADC system is only going to be as good as the Vref in terms of noise and stability. And that's one of the reasons why when all is said and done even the best 3458a is only good for several low ppm for DC accuracy, and they are not longer-term DC transfer accurate instruments. Notice there is also a 24hr accuracy / uncertainty also that is much higher than what 8.5 digits seems to be offering.NOW: For one solution, I know how its done for critical absolute measures at an aerospace company for space vehicle instruments: You don't rely on ONE 20 or 24 bit ADC. You average not from one ADC / Reference but you have to average across 5ea. ADC's each with their own Vref. So five different -systems- involved feeding the digital math filters. And that will get you down to around a good 1 or maybe 1/2ppm stable absolute measure: say 20 or 21 bits. It's hard to get past that. It can be done... but you have to get more creative for reading an absolute voltage value without having a JJ-Array on hand.You can try filters on the Vref with really, really low cutoff freqs, but then you realize how long it takes to stabilize after power up <Laughing> and that still doesn't address 1/F noise.If you look back at Jim William's Linear Tech app notes on true 1ppm voltage refs - notice there are always 3 or 5ea. 3458a's involved? That's what it takes to get into those low uncertainties.Did you notice the price of 250x chips? What happens to the cost when you need 8 SIMULTANEOUS inputs? Yikes! The customer isn't going to like that...

author: Kleinstein
author_rank: Super Contributor
timestamp: April 17, 2017, 07:03:51 pm
content: It should not be important which version of the LT1013 is used. So even the SO8 version should be OK - though the DIP version has advantages (less sensitive to board stress). The LT1013 is very convenient because it is single supply. If one has a negative supply available anyway, there might be alternatives (still BJT base and otherwise quite similar to the LT1013) with slightly better specs, but the OPs don't make a big difference anyway. The amplifier following the reference circuit will have a much higher (e.g. 200 times) influence - so that choice is important.The choice of resistors and the thermal layout (board and case) is much more important than a little less noise or drift of the OPs.For compensating residual TC with R9 (the 400 K resistor in the LTC1000 circuit), this effect depends on the temperature setting and the thermal design. It uses the change in heater voltage as a temperature dependent part. This is more like indirect and nonlinear in temperature, especially with a low temperature setpoint. So there is no such universal number saying an extra 1 M gives a certain change in TC.

author: VK5RC
author_rank: Unknown
timestamp: April 18, 2017, 11:33:41 am
content: Hi TiN et al,Thank you for doing so much work and publishing the results - it seems to be providing some interesting discussion points.I would be happy TiN if you want to try anything with that unit e.g. R9 etc. Let me know the parts costs and I will happily reimburse you.The LTZ is mounted a little high (I used forceps as a heat sink when soldering) so it is about 3-4mm above the board. I have a quote request in place for some of Edwin's 13k pww resistors to replace the 12k.Robert

author: Andreas
author_rank: Super Contributor
timestamp: April 19, 2017, 08:13:44 pm
content: Quote from: MisterDiodes on April 17, 2017, 04:27:05 pmThanks for the link.It confirms that I have it done all right in my design (mainly against EMI).Every input of a OP-Amp is at least filtered with 22-100nF so that the poor LTZis not scared if I take a chopper OP-Amp instead of the LT1013.With best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: April 19, 2017, 08:33:39 pm
content: Quote from: Kleinstein on April 17, 2017, 07:03:51 pmHello,I have to disagree.The SO8-version is only available in D or I grade which is specced with double value in offset drift.When you regard the worst case with 5 uV/K and a temperature span of my lab of 18- 33 deg C (15 deg span):this may give about 75uV drift in tempererature setpoint voltage corresponding to around 2 ppm drift in output voltage.so the max 2 uV output voltage drift due to the LT1013 over a 50 deg C span is valid only for the "typical" value of the A-grade of the LT1013.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: April 19, 2017, 08:47:27 pm
content: Quote from: VK5RC on April 18, 2017, 11:33:41 amHello,if you plan to do any changes on the key components it does not make sense to experiment with R9 now.The T.C. sensitivity might change with a different setpoint.The 3-4 mm above the board also let not much room for improvement.I would let at least 0.5 - 1 mm play between the board and the body of the LTZ. (no board stress directly on the body).From full length to nearly zero length I got about 0.12 ppm/K difference.With best regardsAndreas

author: Echo88
author_rank: Frequent Contributor
timestamp: April 20, 2017, 12:37:55 pm
content: @ MisterDiodes: Always a pleasure to read about your experiences, especially since i have the 2508-32-Evalboard sitting in a corner!Maybe you can have a look at the proposed voltage-reference-filter-design mentioned here and share your opinion:http://electronicdesign.com/energy/filter-trims-ultra-precision-voltage-reference?Also: do you know any good ref-filter-design for a LTZ1000 regardless of the stabilizing-time?Edit: Since the LTZ1000/Ref-Amps are the best voltage references out there apart from the superior JJA and companies like Fluke/Keithley surely like to improve their stuff: Do you know of any successful projects which improve stability/noise of those references or does it just not make sense and the only good way is to handselect and parallel those references like it is done in the Datron 4910?

author: VK5RC
author_rank: Unknown
timestamp: April 20, 2017, 01:05:03 pm
content: Hi Andreas,The other parts (13K) will be mainly for my other two LTZ references, re R9,ifTiN is interested and has the time I thought it might be an interesting experiment. I can't get easily such nice data as he is able.Robert.

author: TiN
author_rank: Super Contributor
timestamp: April 20, 2017, 02:14:31 pm
content: I'll play with compensation resistor. Best case would be after this to leave this reference be, and use it as comparison vs rest of the references.But that will be next month, as all my gear is tied up now, running other python snakes, and I have few more items to clear out first.For time being it's attached as is to my scanner setup (2x3458A/K7168) with rest of the LTZ crowd for logging.If we get tempco fixed (<0.05ppm/K), then VK5RC could use this known tempco ref to test his own 3458A tempco, so he could later "transfer" better stability into rest of his LTZ's.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: April 20, 2017, 05:42:44 pm
content: @echo88,I remember this article, while there is some reduction in 1/f noise from this filter, the application of it with a LTZ reference is questionable. First, the LTZ has significantly lower noise than any of the Maxim Vref chips, the lowest appears to be about 4uV P-P typical vs. the LTZ's 1.2uV P-P. In the case of the LTZ, the filter would also increase the DC drift of the output noticeably, there are always trade offs to be made and frankly I doubt this filter will reduce the 1/f noise of the LTZ all that much. In this case, the trade offs of perhaps slightly less 1/f noise vs increased DC drift is likely a washout at best.I also question the measurements being done with a DVM, it is a sampling/averaging device by nature and therefore is not the best instrument for measuring P-P waveforms, an analog o'scope or strip chart is much better or perhaps a spectrum analyzer. 1/f noise averaged will not produce an accurate result and that is all a DVM can do. Of course, comparing a DVM's averaged noise measurement has some small indication of 'total' noise but nothing more. You simply cannot average out 1/f noise.The best noise reduction technique is to use the lowest noise components in the circuit, since the LTZ represents the lowest in noise available, that leaves the other components, the LT1013 is intended to be used with the LTZ, it was designed with that in mind and the lowest resistor noise components are wire wound. The next level of noise reduction is the circuit layout and power supply noise. There are always trade offs in circuit designs and you have to pick the places in the circuit where you can reasonably reduce the noise, unfortunately filters in this case are very difficult to implement when you're working at such low frequencies and the DC output is also very important.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 20, 2017, 06:46:39 pm
content: The main source of 1/f noise in the LTZ reference it the LTZ1000 itself. So there is not much to gain from using super high quality OP or resistors. So the obvious choice would be a slightly higher current for the LTZ1000 or two of the references in parallel. Also an other, lower noise reference and slow compensation of the long term drift of the low noise reference might be an option.This filter circuit adds twice the noise of the OPs. So for a low noise reference it needs lower noise OPs, which will cause more current noise and possible drift. The listed MAX4238 is specified at 1.5 µV_pp für 0.1 - 10 Hz. So you trade in a reduction of the 1.2 µV_pp by an additional about 2.1 µV_pp from the 2 OPs. So the OPs uses should be much lower noise, more like LTC2057.The 0.1 -10 Hz frequency range is used in datasheets, because it can be measured in reasonable time and with analog AC coupling. However in many applications of a stable reference the actually interesting noise could be the 0.001 -0.1 Hz range. Filtering is even less practical here.Using a DMM to measure the LF noise is not that bad. However one has to include the averaging of the meter as part of the filter that sets the bandwidth. With fast enough readings (e.g. 1 PLC) this should not be an issue. The more important point could be noise of the input amplifier - so it might need an extra amplifier stage or a low level meter like the 34420.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 21, 2017, 03:47:03 am
content: Quote from: Echo88 on April 20, 2017, 12:37:55 pmHa! That circuit's been floating around a while for sure, in various forms. Nothing to see there, and a poor ad for Maxim - another capacitance multiplier. A great teaching moment in 1/f noise and how hard it is to get rid of.Just try building a LP filter with cutoff down in the 10's of mHz - watch what happens when you turn it on. You'll be waiting a while... <Grin> You'll still have noise over longer time spans now, and you'll be kicking yourself for blowing that much on those $65 caps, etc.You don't need the "Teflon standoff's" either if you understand guard circuits - and you sure don't need that extra shunt regulator. That was there just because those goofy Maxims were only 5V parts - typical of the early crop of AZ amps. Noisy buggers also, compared to later offerings. Maxim seemed to always miss the mark there.Not making noise in the first place is the concept, and paralleling Vref's (up to a point) is probably the better bet. Probably 9 or 10 Vrefs is a practical limit and point of real diminishing returns. 4 Vrefs might be even a better upper limit. Only if the customer is willing to pay though.If you build this stuff for a living, you'd better make sure there's a practical sense of profit also. If you chase low PPM's for no real reason and no profit - you'll be out of business.At some point you have to tackle the problem the other way and decide what noise you can live with...and what is "good enough" if you have multiple measuring systems. The 3458a has great linearity and has good resolution for relative measurements over shorter time spans. As good as it is you still have 1hr, 10hr and 24hr uncertainties that are unavoidable - and that's why the most practical approach is to average acrossmultiple systems(Vref and ADC or whole DMM's) to help deal with 1/f noise.Better yet is to spread your measurements acrossdifferent devices and techniques- so that why we have 3458a's as well as 732's, KVD's and null meter sets. That way you get a better spread of drift rates and noise, and more likely to fence in an accurate estimate of a DC voltage. What you don't want is everything drifting together with similar 1/f noise characteristics.Remember: It's always only an estimate measure when you're in low PPM territory. Even a JJ-Array has uncertainty. Most of the time trying to spend an exponential amount of effort trying to shave another half-ppm of uncertainty is a major waste of time AND money.

author: TiN
author_rank: Super Contributor
timestamp: April 21, 2017, 04:18:10 am
content: Quote from: MisterDiodes on April 21, 2017, 03:47:03 am$65? Cheapskate! How about$707?QuoteHm, you got me an interesting idea for that old DMM noise test experiment. Sample 4 DMMs (2x3458 + 2x2002's) in sync together and average their common result minus the offset, to get total noise figure. That could show if noise of such rig lower than single DMM.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 21, 2017, 04:44:17 pm
content: Again: Learn from the app notes where 1ppm-level values are being tossed around. You'll never see just one DMM being used, it will be usually 3 or 5 units at least.TiN: Using a $700 cap is unfortunate- let alone a $65 X 2 in that rip-off Maxim LP filter circuit (Burr-Brown was doing that in the 80s, and I think they ripped it off the idea from maybe National, if I remember right). The original idea dates back to mechanical chopper / tube days. If you're having to buy those caps, there is -probably- a better way; or you're not really selling the circuit for a living. The real companies that use wet tant caps won't be paying $700 a pop, guaranteed.Here's the rule: If you don't like the price of a component, you're not buying enough per year.Just some other random thoughts here...Even more stuff that has nothing to do with "Story of Little Jumper"Now class, looking at that Maxim circuit (Which is doubtful it was ever used, it's just an ad for a trade rag) - someone tell me how long it takes to charge that 10uF Teflon cap C1 via 3M at the input to let's say a 10V Vref to within 0.1ppm of Vref (where you'd like it to be to start stabilizing output). Now look at how long it takes to charge that second cap via 1M (actually, what is the net charge across second 10uF Teflon cap?). Like I said, you'll be waiting a while. You'd like to use the circuit in some reasonable amount of time. "Reasonable Time" might be open to interpretation here - but this is something you have to calculate if you're designing a real project. Maybe the device is left on all the time...or maybe the device has to be battery powered, in which case you don't want to wait a long time after power up before you can even measure anything.Your end application makes all the difference here.Back to Maxim circuit:WHOops...Now check the influence of that op-amp input DC and noise current and overall effect of amp switcher spikes, and how does that affect charge time and accuracy? With a 3M resistor is place and the op-amp running, what is the net effect of switcher current spikes when they are not exactly bipolar / cancelling in nature? (That's the other dirty secret of AZ amps ). Will that cap C1 gain or lose more charge over time, and what noise effect does that add to the output?WHOoops...What happens when you power off or glitch the power rails (maybe another device fails on the power rail)? That 10V stored on the cap C1 has to go somewhere, and that input pin and internal surge diode on the amp is the only real path. Now you find out how fragile that diode in the amp is. You learn to look for this in amp circuits whenever you see a larger cap hanging off an input pin directly, with no limiter resistor. That's a red flag right there nobody really used that circuit in practice - or never designed for reliability.And on and on and on.That capacitance multiplier filter isn't a very good approach, and its doubtful it was ever put into real practice beyond a trade mag advertising blurb. For the cost of that filter you could add another paralleled LTZ and resistors at least.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 21, 2017, 05:28:32 pm
content: The filter circuit with the OPs as shown would have a background noise level of around 45 nV/Sqrt(Hz) (more at low frequency) from the OPs and the additional high noise from the AZ switching (in the 10s of kHz range). So about the noise level one could get from 2 LM329 in the kHz and above range. So if you start with a good reference like the LTZ1000, noise at the output would be higher than at the input side.The bias current and current noise should not be such a big problem here: the input impedance seen at higher frequencies is relatively low and the bias current is still low for the modern AZ OPs. Even lower noise AZ OPs are often below 200 pA, and this bias is relatively constant over temperature. The offset of A1 is not critical at all (maybe 1 mV DC at the filter cap), and A1 sees a 10 K input impedance. Thus only 1 µV from a 100 pA input bias.Still the circuit should have a second passive filter stage (before A2) to get rid of much of the higher frequency noise of A1.One possible nasty part hidden in this circuit is dielectric absorption in the C1 capacitor. The RC time constant is something in the 300 s range, thus something like 1 hour waiting to get it stable - however dielectric absorption can be a really slow process, depending on the capacitor.

author: TiN
author_rank: Super Contributor
timestamp: April 22, 2017, 04:00:50 am
content: MisterDiodes, little jumper is working happily since, other than jumpy, it's actually stable. And to be fair, those wet slug caps are not for any kind of filter, they are bought for far less than mouser list price for AN124 style low-noise preamp.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: April 22, 2017, 04:33:10 pm
content: CORRECTION to my previous post:The capacitors mentioned in the Electronic Design mag article above - 935C1W10K - are not $65 as I wrote above, but I see TTI has some for $19, generally around $20~$25ea. elsewhere. Somehow I was guesstimating the BOM cost of that LP filter circuit with newer AZ amps, and that number stuck in my head. It will still take a very long time to settle, important if you're building some sort of battery powered application.Sorry about that. My gift is I know everything there is to know about everything, my bane is I just don't know it all at the same time

author: ap
author_rank: Frequent Contributor
timestamp: April 22, 2017, 06:25:36 pm
content: There are other PP capacitors available at a much lower cost per uF.

author: Echo88
author_rank: Frequent Contributor
timestamp: April 22, 2017, 10:20:05 pm
content: Thanks MisterDiodes and Kleinstein for dissecting the circuit. Since theres no real cost-effective solution to improve those LTZ1000-references i will stick with temp-stabilizing my reference and be done with it.

author: Keith956
author_rank: Regular Contributor
timestamp: March 10, 2022, 06:38:49 pm
content: Sorry to revive this old thread, but I thought I'd have a go at this reference. Boards from OSHPark arrived and look good. I have most of the parts on order, except for the Vishay resistors. Where do people get these from - direct from Vishay?

author: Andreas
author_rank: Super Contributor
timestamp: March 10, 2022, 07:16:50 pm
content: Hello,in the US: Texascomponentswith best regardsAndreas

author: Keith956
author_rank: Regular Contributor
timestamp: March 15, 2022, 04:01:46 pm
content: Thanks Andreas,I have a question on the resistors. In the xdevs schematic, it shows the resistors as:R3 120 0.1%R4 1K 0.1%R5 12K 0.01%R6, R7 70K 0.01%And in the BOM it shows them asR3 120 0.01%R4 1K 0.01%R5 13K 0.01%R6, R7 70K 0.1%Which is right? Does it matter? I'm using a LTZ1000CH not A version).

author: TiN
author_rank: Super Contributor
timestamp: March 15, 2022, 04:13:14 pm
content: 13k is correct abd suitable for usual conditions up to 40C ambient.

author: Keith956
author_rank: Regular Contributor
timestamp: March 15, 2022, 04:16:59 pm
content: Quote from: TiN on March 15, 2022, 04:13:14 pmThanks! And the tolerances? 0.01% for all?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 15, 2022, 04:25:03 pm
content: No need for tight tolerances. 2% is well good enough and many could even be 10% if you can find them. The nominally 70 K could be somewhere in the 50-100 K range. For R4 , R5 only the ratio really meters. So 20 K and 1.5 K would also be an option.

author: Andreas
author_rank: Super Contributor
timestamp: March 15, 2022, 08:02:17 pm
content: Quote from: Keith956 on March 15, 2022, 04:01:46 pmIt depends on your environment temperature where the LTZ will work.For the non-A version common understanding is not to go below 12K for R5 up to 40 deg C environment temperature.One of my LTZ1000 (#8) needed a trimming with a parallel 22K1 to the 1K resistor in order to get a better T.C. linearity above 33 deg C.https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2301414/#msg2301414Generally I would use 0.1% or better resistors for R4+R5 in order to have the ratio tolerance within +/-1 deg C (+/-2mV) to nominal ratio.(of course the Zener voltage tolerance will add addtionally setpoint tolerance).with best regardsAndreas

author: Keith956
author_rank: Regular Contributor
timestamp: March 21, 2022, 05:21:02 pm
content: Quote from: Andreas on March 10, 2022, 07:16:50 pmIs resistorinfo@texascomponents.com the right email for them? I sent an email a couple of weeks ago asking for a quote for resistors and got no reply.thanksKeith

author: Andreas
author_rank: Super Contributor
timestamp: March 21, 2022, 07:12:28 pm
content: on the webpage they have a different E-Mail see:http://www.texascomponents.com/store/home.asp

author: Keith956
author_rank: Regular Contributor
timestamp: March 21, 2022, 08:14:22 pm
content: Quote from: Andreas on March 21, 2022, 07:12:28 pmHmm, not sure where I got the email address I used from! I will give that one a try.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 21, 2022, 10:13:38 pm
content: Hi Keith,as you are located in the UK, you might have a look on precision wire wound resistors, 'econistors' or BMF from Alpha Electronics, FLCY, which are available on stock from rhopoint electronics in your country.I have successfully built very stable references with both technologies; the Vishay ones are technical over engineering and budget overkill.0.1% is fully sufficient for all 5 resistors.Frankhttps://www.rhopointcomponents.com/product/components/resistors/precision-ultra-precision-resistors/general-resistance-8g16-econistor-series/

author: Keith956
author_rank: Regular Contributor
timestamp: March 23, 2022, 06:48:48 am
content: That is good info Dr Frank! I did get a response from Texas Components but the minimum order quantities are 10 per value which would be expensive unless I could get enough interest for reaching the MOQ. These look good but of course they are only 5ppm/C not 0.2ppm/C.Keith

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 23, 2022, 09:35:33 am
content: the Vishays are 0.2ppm/K typ. only, see datasheet for their max. values, instead.I also bought these 0.05ppm/K Z-types, just to measure them as having 0.3 ... 1ppm/K.the econistors might have between 1..5ppm/K, you need to characterise and match them, but the attenuation factors are so high that you can ignore their influence on total T.C. and you need to trim that anyhow.Most dominant is the LTZ itself.The bmf types are typically 1ppm/K.I like the PWW, because they have lowest hysteresisFrank

author: Keith956
author_rank: Regular Contributor
timestamp: March 23, 2022, 07:17:09 pm
content: Thanks you Dr Frank, that is very helpful.Keith

author: Keith956
author_rank: Regular Contributor
timestamp: March 24, 2022, 10:04:02 am
content: Just to add I had a quote from Rhopoint here in the UK for the resistors Dr Frank recommended. At between £5 to £8 each in 1 off quantities they are a lot cheaper than Vishays. I think I'll give them a try.

author: TiN
author_rank: Super Contributor
timestamp: March 26, 2022, 03:32:03 am
content: Quote from: Dr. Frank on March 23, 2022, 09:35:33 amMy experience shows that such generalized statement not exactly true for all PWW, many PWW are much larger hysteresis then expensive BMF (VHP10x, VHA, etc).There are many very different PWW constructions and designs so while some have excellent performance specs and low hysteresis, many others are not so great. And PWW can be more sensitive to handling and physical implementation of design.I'm not saying BMFs are best there is, but if budget and schedule (9+ months lead time is normal, even way before current chipmageddon times) allows it, they often provide performance without much selection.

author: syau
author_rank: Frequent Contributor
timestamp: March 26, 2022, 04:04:17 am
content: Have ordered some Vishay from ELcoPC, West Chester last October 2021, package now on the way to me.VPG VHP202Z Z-Foil Hermetically Sealed Oil Filled Resistor cost between $50 - $85 (not sure why have such huge price range)VPG VHD200 BMF Small Package Ult. Track. Herm. Voltage Dividers cost between $37 - $40All are 0.01%. “EXPRESS LINE” service added $1.2k

author: syau
author_rank: Frequent Contributor
timestamp: April 02, 2022, 03:34:20 am
content: After taking some effort to clear the USA Custom, received the parcel today.

author: Keith956
author_rank: Regular Contributor
timestamp: April 08, 2022, 08:32:37 am
content: Well all the parts arrived and last night I built the board. Checked it out and hooked up to a 12V power supply and measured the Vref with a calibrated HP3458A. So far it's looking good with the output 7.008220 and noise down in the 1-2uV, time to leave it on to burn in.Some comments about the board for anyone else building one. The PCB (rev B03):- It would be nice to have capacitors labelled on the silkscreen. True there isn't much room but at least C4 and C8 could also be marked.- Add holes for mounting the board on standoffs. This would mean a bigger board but then more component info could be added too.- The low tempco resistors were mounted vertically, fortunately they just fit.- The BOM on the xdevs site misses R9 (0 ohm), R12 (2.2K) and VD1 (LED).- The pin numbers of Q1, 3904 are incorrect on the schematic.- The silkscreen could show the tab on the LTZ1000. OK so you can figure it out.- The silkscreen should show the polarity for J1 and J2. Again this may need the board being slightly larger.- I'd have liked to see some protection from reversed power supply connection.These are not criticisms of the good design just suggestions.Keith

author: nedrysoft
author_rank: Contributor
timestamp: February 23, 2023, 05:15:05 am
content: Hi,I’m just about to build one of these, I’m waiting on the PCB to arrive from OSHPARK, I managed to snag the ltz1000ach from mouser.The only parts I’m missing is a couple of the Vishay resistors.I have seen talk of alternative parts, so I’m asking the following questions with the fact that this thread is over a year since the last result, given the great conponent famine I’m hoping people will be able to make suggestions.So does anybody have a source for these Vishay parts, I have the 120R and the 1K foils but the remaining ones seem harder to find, I should also probably mention that I’m based in the U.K as that may impact on availability of either Vishay or alternatives.I saw mention of Rhi point in the U.K. and I’ve contacted them and waiting for a response, although 13K isn’t a standard econister on their site so I had to select custom, so I’m not sure whether they are able to supply such low quantities.Obviously I am at the mercy of what’s available and what companies will deal with individuals.Furthermore I have seen the offer of calibration services being offered by members, are people still willing to offer this service should I manage to source the remaining missing resistors.Many thanksAdrian

author: Kleinstein
author_rank: Super Contributor
timestamp: February 23, 2023, 07:49:38 am
content: IT looks like Mouser still has 1 piece of 13 K BMF (S102K) in stock, at least from Germany. The 13 K are used as a divider with the 1 K so should ideally be the same type.The 70 K resistors are supposed to be a bit less critical and the values does not have to be exact 70 K. Smaller slightly increases the TC before regulation, larger slightly increases the noise.Good thin film types may be good enough.

author: nedrysoft
author_rank: Contributor
timestamp: February 23, 2023, 11:27:33 am
content: Thanks, sadly by the time I was able to look somebody else had bought it.I’m waiting on a response from rhopoint to see if I can get the required values of resistors from them, I’m happy to wait for the right parts to become available, I have the bulk of the components including the ltz1000ach which was up until yesterday, the problem part, but I checked at 2 or 3am this morning on the off chance that some were in stock.

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 23, 2023, 03:18:09 pm
content: Please have a look into the big 'Ultra Precision Reference LTZ1000' thread, for different values of the resistors.I have published a table for all my references, which resistors I have used (econistors from G.R., or BMF from AE, supplied by Rhopoint) and which oven temperatures I have measured.https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3263778/#msg326377813k/1k (divider ratio of 14) gives an oven temperature of around 70°C, which I do not recommend at all for long-term stability.12.5k/1k gives about 60°C, and 12k/1k gives 50..55°C, which I have used for all of my references, A-type as well non-A.Depending on your application, you could also run the A version on that lower temperature, if your lab temperature is never higher than ~35°C.12k is available at Rhopoint as standard value for an econistor, I don't remember if this value was also available for the BMF seriesBMF resistors with 10k / 800 will give the 13.5 ratio for 60°C, and 10k / 900 gives 13.11 ratio, as a replacement for 12k/1k.FrankPS: 12k is not available for BMF. As can be seen in the link above, I have used BMF resistors 120 Ohm, 1k, 2x 70k, and a 12k econistor, the green one.

author: nedrysoft
author_rank: Contributor
timestamp: February 23, 2023, 06:18:00 pm
content: Many thanks for the reply, I appreciate it.I’ve had contact with rhopoint so I will be getting them from them, just going through the invoice back and forward.My mouser parts have shipped as well.