A Voltage Reference Lab Experiment: ADR441 "Burn-In" 1000 Hours (10 ICs) - Page 1
Forum section: electronics / projects

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 04, 2013, 01:52:40 am
content: I was kindly given a free of charge sample of 10 x ADR441ARZ by Analog Devices, Inc. Four of them are up and running as I write. All ten will be powered under 'controlled' and different conditions for 1000 hours (or more). I hope to use this thread to gather information and learn about 'burn-in' and 'ageing'. I will go to no 'extremes' like +125/-40 degrees Celsius and 'damped cycling' for 'nulling' of thermal hysteresis and similar treatments. Solder iron, sun, fridge and freezer it will be. After all - it's just a few (good but not best) precision chips ...Will be interesting to see what comes out of this. There is quite a lot of (different ?) 'knowledge' and experience distributed on this forum. I for one am in for learning ...

author: Vgkid
author_rank: Super Contributor
timestamp: November 04, 2013, 03:05:26 am
content: I can't wait to see the results of this.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: November 04, 2013, 05:06:33 am
content: This should be goodDo you have means to seal one or two against humidity? I've been thinking about performing similar aging tests with some REF102, and I've been thinking how I could reasonably isolate them from humidity (which varies quite a bit in my environment, and I'm guessing is the dominant source of instability in my REF5050.) One of DigilentMind's posts planted some ideas, but I have yet to pursue them.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 04, 2013, 06:53:54 am
content: That part is specified at an initial accuracy of ±3mV , which is ±0.12%. The 4 parts you showed were actually much better than this1) 2.50034 = +0.014%2) 2.49982 = -0.0072%3) 2.50035 = +0.014%3) 2.50021 = +0.0084%In the same way that averaging N samples of an ADC input will give a more accurate reading from the ADC, it also works with references. You can average these 4 references using a low-offset opamp in an inverting divide-by-4 configuration, followed by an inverting unity-gain buffer. Obviously, the divider should use precision, matched resistorsavg: 2.50018 = +0.0072%Now, this is the same accuracy as reference #2, but the point of the exercise here is that you can get this with a bunch of references, without knowing the exact values of each reference. .. i.e. you can average 10 references and get a more accurate reference.Bob Pease had a segment about this on the Bob Pease Show.This becomes clear when you look at the typical gaussian distribution of the initial error, in the datasheet:

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 04, 2013, 07:58:43 am
content: Yes, I hope it will be fun too.When it comes to humidity, I don't know. I am soldering the next 4 now on a board. The last two - code names 'The Black Widows' - could be placed in a small medication glass bottle with a resistor/transistor heater. And then maybe sealed after drying out. There is enough time (990+ hours) ...Averaging is the plan. Use the 4 best ones to make 5V or 10V. But we must know them separately first. When averaging there will be a compromise between voltage sum (close to target), direction of drift and noise.When I asked for these devices I think I said 'a handful different references from the ADR44x family'. I was planning to compare them to my LTC6655 2.5V and 5V references. Both are low noise references.But since I was given the A Grade (which according to specs is nominally 3-5 times worse than the B Grade in tempco), it is not really fair. I am OK with these devices - fun to have 10 equal chips coming in that elaborate packet. And if ADI sees that this thread gets x000 views, I'm sure they will give me a few ADR4550 B Grade for comparison. Anyhow - it is not the result that matters - imo the experiment has value in itself (even if it was for 10x 78L05).I am all open for ideas for treatment of the refs. But I need to get them all running first ...Datasheet for the 10 samples:http://www.analog.com/static/imported-files/data_sheets/ADR440_441_443_444_445.pdfDatasheet for the 'best' in comparable devices from ADI:http://www.analog.com/static/imported-files/data_sheets/ADR4520_4525_4530_4533_4540_4550.pdf

author: Harvs
author_rank: Super Contributor
timestamp: November 04, 2013, 01:28:12 pm
content: Quote from: quantumvolt on November 04, 2013, 07:58:43 amHow about just stuffing them in a small vessel with a fresh desiccate packet?

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 04, 2013, 02:14:43 pm
content: Quote from: Galaxyrise on November 04, 2013, 05:06:33 amQuote from: Harvs on November 04, 2013, 01:28:12 pmVery interesting you mention this. Problem is the parcel came from the Philippines in the Pacific. Even wetter than Thailand where I am. We are in the end of the humid rainy season. I will use a few days to think about it. I think they should be run hot in order to dry them out. Will also help on the tempco problem. We'll see.But it brings up another thing. I did my first sample request at the age of almost 60. I really want to buy and pay for the stuff. But the shipping costs are prohibitive.Another big chipmaker has Asia HQ in Bangkok. I want to buy a chip at USD 2.36 a piece. But the shipping cost is more than USD 20. Real postage (560 kms / 350 or so miles) with Thai Post is 70 cents or so.Result: If it can't be found on fleabay, I will now sample stuff, not buy it. If it can't be sampled, I will just forget it ...

author: branadic
author_rank: Super Contributor
timestamp: November 04, 2013, 06:25:15 pm
content: Do you have the possibility to package the references on board to a hermetically sealed package? I'm thinking about hybrids like shown here:http://www.elbau-gmbh.de/de/produktloesungen/mikrosystemtechnologie/packaging/gehaeuseverschlussSeems that there could be enough space for a MSOP8 reference on a pcb/dcb.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 04, 2013, 09:42:21 pm
content: The hybrid "capsules" look very nice. Interesting concept (never knew you can get a "TO-3 style" package for DIY/Custom hybrids).But I feel it is overkill for these refs. Their specs are not outstanding. And also it will be more work and waiting time to get housings.Right now I feel more like "negative" testing of the chips in order to see if maltreatment produces any detrimental effects. Specifically I think of 4x in room temp, 4x going through fridge/solder-iron-heat-element-close-contact (10 hours just a few mm's from a 30W iron) and the two last ones placed on the weather-exposed balcony in an empty plastic water bottle (4 wires for 5V supply and measurement of Vref).I am sure I can get some references more worthy of super-care (but I already have some 10-30 references including LM399, LTC1236 and AD586LQ and many others I have yet to power up). The point with the 10x ADR441 from the same production batch is imo to see if they are somewhat "equal" after time and bad treatment. However - 10 pieces are not enough to make generalizations from.Anyway - I need a week to make a "test rig" with a PSU, MUX and 10 Ch. C++ program. My experience is that after continuous powering a week the refs will have somewhat stabilized and can - after measurement - be subjected to different treatment.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 05, 2013, 01:07:16 am
content: I don't think they will be the same after several sessions of bad treatmentHowever, what you are doing is characterizing them. If for example, you were considering a specific reference for use in your company's SuperSaunaMaster one-hour auto-sauna calibrator. That instrument might live in the back of a pickup truck in North Dakota during the winter, and Mr. Joe the sauna repairman is called out, so he runs out to get his instrument and uses it in the sauna while the auto-calibration is taking place (good job!), collects his pay, then throws it back into his truck again for overnight or until the next time hegets to use the sauna againcalibrates the sauna. So you want to know how that reference behaves after repeated cycles of -20C to 80C back to -20C . Then you can write a datasheet for your instrument that says it is within X% of true, where X covers the range of extreme changes you measured while characterizing it in your lab as you are right now

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 05, 2013, 08:37:56 am
content: Quote from: codeboy2k on November 05, 2013, 01:07:16 amI like the way you describe it. Characterizing.I am searching uses of the word "burn-in" now, and it turns out that there is only vague descriptions of the term. Duration is from "short time" and 168 hours (1 week) here, 200 hours there, and 300+ hours to 1 month other places. Obviously - these numbers are more or less picked out of the blue (or based on experience - not theory).Furthermore - the temperature 125 deg C is used just because it happens to be the usual data sheet upper limit. Not in any way a physical law of nature or a magic number.I will collect and document what I have found (which is not much). But it is clear to me that there is no obvious DOCUMENTED "best" way to stabilize a reference. And according to a wiki page the goal of "burn-in" is to force early failure of inferior devices (which is somewhat different from "forced maturation").So the concept of "characterizing, conditioning, breaking in, field testing, burn-in, cycling, ..." has imo many and unexpressed meanings.I would guess that as long as you don't subject the devices to more extreme conditions than what the data sheet allows, and if you use time waiting for "real" ageing (as opposed to fast ageing by burn-in), the refs will be OK and settle unless we are talking about a single case monday/lemon chip.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 05, 2013, 08:51:18 am
content: In the two videos below the references (GR1-GR4) are powered by 15 V DC from a Chinese wall wart. In the first video in an earlier post, they are powered by an almost dead 6 V (9 V nominal) battery.The first video is at room temperature 28.1 deg C and the second at 31.4 deg C (I assume both numbers have the same error), so there is a temp diff of around 3.3 deg C.It turns out that the worst ref has a tempco of around 7 ppm/deg C and the other around 4-5 ppm/deg C (which in all cases are better than the data sheet specs).Room temperature 28.1 deg CRoom temperature 31.4 deg C

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 05, 2013, 09:08:48 am
content: The next four (WH1-4) will be powered tomorrow. Nice paint job?(couldn't stand the brown cheap PCB ...)

author: Andreas
author_rank: Super Contributor
timestamp: November 05, 2013, 09:50:21 pm
content: Quote from: quantumvolt on November 05, 2013, 08:51:18 amYou have forgotten the different self-heating of the ICs.Quiescent current 3mA for the reference times 15-6V = 27mW difference.27mW * 130 K/W = 3.51 degrees more chip temperature. So temp diff is around 6.8 degrees.Regarding A and B grade: since the characterisation is done only at 3 temperatures the difference in tempco is mainly at the temperature extremes. The behaviour at room temperature can be better on a A grade than on a B grade.To your measurement setup: the 3 mA produce a voltage drop at the Gnd lines. The voltage of the references is specified directly at the output of the pins and not necessarily at your common gnd.In my ageing setup with around 30 references I have about 60uV voltage difference between the gnd pins of the references. (which are measured and calibrated out).The 2.5V references with your resolution of 10uV in the 10V range produces a 4 ppm resolution per 10uV step.You might wish to get a better resolution. With a stable 2.4-2.6V reference (eg a aged LM399 with a LT1043 voltage divder) you could use the 100mV range with 0.1uV resolution.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 05, 2013, 10:18:56 pm
content: Quote from: Andreas on November 05, 2013, 09:50:21 pmThanks for posting Andreas - it is always nice to have your expertise with us.Re self-heating: Yes, I know. It is just a misunderstanding. There are 3 videos:- [#01] Unknown temperature, Vin around 6 V- [#02] Temperature 28.1 deg C, Vin around 15 V- [#03] Temperature 31.4 deg C, same thermometer and Vin as in [#02]So briefly - the first reference GR1 on the green board - shows2.500112.50056 and2.500152.50059 in video 2 and 3 (same Vin, different temperatures). This is bit less than 5 ppm / deg C.The reason I mention the first video is that someone might be interested in knowing that the differences in measured values from the first to the second video will also be influenced by line regulation. This effect is absent from video 2 to 3.Re tempco: I have never thought of that - the low tempco devices are picked by ATE so that they fulfill the specs for the full range of 0 to +70 or -40 to +125 deg C. But obviously - now that you have said it - the standard grade can be just as good or better for single chips in the range 20 - 40 deg C (which is all that interests me). Nice to know.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 05, 2013, 10:48:02 pm
content: When it comes to wiring and measurement I will fix that today. Do you see the 1602 display to the left in the first video? It is an Arduino reading RS232 output from the 34401A with 7 or 7.5 digit resolution (I have proved in another thread that the 34401A dissolves 1 ppm - see video below).Also the 8 refs that are soldered up (GR1-4 (green board), WH1-4 (white board)) will go on a motherboard (just a piece of plastic) with a remote transformer (no SMPS) and on-board linear regulator with decent ground sense-force and increased resolution/average/min-max (P-to-P noise)/(later RMS noise) measurements today.---Agilent 34401A detects a 10 ohm resistor in series with the voltage reference connected to its 10 mega ohm input - i.e. 1 ppm. The "square wave like steps are the resistor connected in/out of the measurment wire.

author: Unknown
author_rank: Unknown
timestamp: November 05, 2013, 11:59:41 pm
content: Hi, I have a couple of questions, the HP 34401A according to the manufacturers specification has an accuracy of 0.0015 + 0.0004 for the 10V range, and that's if the meter is within it's 24 hr calibration; so, I think if you were measuring an ideal 2.5v reference the value the meter read would be subject to +- 75uV; the 90 day cal I think would be +-100uV; but that error is not accounting for the temperature coefficient error which would also add to the final reading.Are you taking the meter error into account in your calculations? Is the meter accurate enough for your needs?

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 06, 2013, 12:31:51 am
content: Quote from: jucole on November 05, 2013, 11:59:41 pmNo, the meter is not accurate enough nor does it have the wanted resolution. But it is the best I have. I will never know the 'real' output of these refs whatever meter I use.Primarily I am only interested in drift - or more correct - stability. The meter's ability to detect non-change or stability is much better than the accuracy (even if the meter was calibrated, which it is not).Later on I will compare 4 stacked 2.5 V refs with a 10 V ceramic chip ref from gellerlabs that is the best documented 10 V ref I have. But whether this ref is in calibration several months after purchase is only guessing (it is calibrated with a HP 3458A when sold). That's the way it is ...

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 06, 2013, 09:14:27 am
content: Eight refs running - named GR1-GR4 and WH1-WH4 (left to right).EDIT:Comments in next post.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 06, 2013, 04:40:50 pm
content: Comments to video in the previous post:The video contains1612 measurements: For the refs WH1-4 there are 8 measurements - 2 for each ref starting with WH4 - with the ground test lead on common star ground and on chip pin 4 GND. The refs GR1-4 has only one measurement each, starting with GR4.For the ref WH4 (far right) - which is measured first of all - it produces a difference of about 20 uV due to voltage loss from the 3 mA supply current in around 5 cm thin test lead. Thanks to Andreas for pointing this out.Since I will may be use a MUX for noise graphs, I have decided not to draw ground sense wires. I am not really interested in the values of the refs, only the change in values over time. The loss in the resistive wires will not change much as the supply current is almost constant. So - knowing that the values are biased - I choose to ignore it.My "board" must be changed a bit, I need measuring test points where the probes do not slip.The supply voltage is now 5V - unregulated DC from a transformer fed to a 7805 and then to the chips.This setup will stay untouched at least a week. Measurements every day.I don't know yet what to do with the last references, so I just keep them for now.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 06, 2013, 04:57:47 pm
content: Quote from: Andreas on November 05, 2013, 09:50:21 pmI would like to do this - subtract a fixed value from the measurement by connecting a stable external ref back-to-back (opposite polarity) so that the resulting measurement is just a few milliVolt (for example 2.50047 - 2.490 = 10.57 (10.57 milliVolt)). But I don't have any aged quality reference yet (I started this madness just a few months ago).But at least now have one more digit that is significant for difference measurements (I only need resolution, not accuracy).

author: Andreas
author_rank: Super Contributor
timestamp: November 06, 2013, 10:21:09 pm
content: Hello,just as comparison:I have tested 1 ADR4550B against my LTZ1000 reference voltage.The ADR4550B is used as reference voltage for a LTC2400 (ADC18)and the LTZ1000 voltage is divided by 2 by a LTC1043.Tempco of the ADR4550B is measured and compensated.So what you actually see is the "inverted" ageing curve.If the reference voltage goes up the LTZ1000 value goes down.Y-axis is the divided voltage of the reference.ADC18 (with ADR4550B) has "aged" by about 100 ppm during 160 days (x-axis).Day zero has started after full calibration of ADC18 (about 4 weeks after "first firing")I have not found an explanation for the "jumps" of ADR4550B.It may be humidity or due to the hysteresis of the device.But since the stability is wide off my needs I will not further investigate on it.Additionally you see ADC13 with a well aged AD586LQ as reference.And ADC4 + ADC8 which have both a well aged but humidity sensitive LT1027CCN8-5.I am curious how the ADR441 compare against the ADR4550B.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 07, 2013, 12:01:36 am
content: Quote Andreas:---ADC18 (with ADR4550B) has "aged" by about 100 ppm during 160 days (x-axis).Day zero has started after full calibration of ADC18 (about 4 weeks after "first firing")---So this means that the ref has been running for around a month before the 160 days plot? Very strange that the Analog Devices 586 is flat, but the Analog Devices 4550 has so much drift. But different chip technology / topology... Very strange - especially because ADI presents it as a very good ref:"For a precision, ultralow noise, 5V reference, we recommend the ADR445 or the ADR4550."Just for sanity check of my setup I think I have a good idea: I add the Geller 10 V and Voltagestandard 5V references to the board, and when I make a graph in the future I present (10/4) and (5/2) Volt together with the ADRs (which are 2.5 volt already).---NB I will edit my previous post from 16 measurements to 12.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 07, 2013, 01:13:38 am
content: Yes, the AD586LQ is extremely stable in that graph.@Andreas, when you say it is "well aged" what does that mean? 1 year? 5 Years? 10 Years?

author: Andreas
author_rank: Super Contributor
timestamp: November 07, 2013, 06:12:23 am
content: Hello,well aged is a bit depending on how the reference itself is behaving. (Until there is only randomly / seasonally change).For buried zener references in hermetically case (AD586LQ) you will typically need a minimum time of 4000 hrs.Some devices will need longer and some will drift infinitely. So if you want to built a good instrumentyou may have to select the about 3-4 best devices out ouf about 20.ADC13 is now running about 2 YearsADC4 is running for nearly 5 YearsWith best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 07, 2013, 08:41:08 am
content: Well - then I have my first multi reference board. Not very beautiful or advanced. But it's the way I am.The most important objection is that voltage values will have bias due to loss in ground force cables. No problem - I am trying to track drift only.So tomorrow I will fix the program in the Arduino (a factor of 10 off when introducing the 10 V ref), and start predictable measurements and look for "theory" and anecdotes in The Gentle (?) Art of Rearing Voltage References

author: codeboy2k
author_rank: Super Contributor
timestamp: November 07, 2013, 07:30:08 pm
content: Quote from: Andreas on November 07, 2013, 06:12:23 amThanks Andreas! ADC4 although aged longer is not nearly as stable as the ceramic packaged ADC13 which is aged less. Is this purely due to ADC4's packaging?Seeing your graph really helps me understand these references better. Thanks for posting that.

author: Andreas
author_rank: Super Contributor
timestamp: November 07, 2013, 08:16:11 pm
content: Quote from: codeboy2k on November 07, 2013, 07:30:08 pmNot purely. But the bare dies of the LT1027 and the AD586 play in the same ballpark.The average ageing rate of the LT1027 is also relative small (around 1-2ppm/year against the LTZ1000). What you see is mainly the humidity difference between winter and summer.Unfortunately the LT1027 is no longer produced in a hermetically package.It would be interesting how they compare to the AD586LQ since hysteresis of the LT1027CCN8 is extremely low.With best regardsAndreas

author: tszaboo
author_rank: Super Contributor
timestamp: November 07, 2013, 09:26:14 pm
content: Quote from: quantumvolt on November 06, 2013, 12:31:51 amThe bigger problem is that your meter will drift 50PPM and your ref will drift another 50PPM according to AD. If we can believe them.http://nandblog.com/why-i-dont-fully-trust-datasheets-anymore/Again, no measurement method for the long term stability...The main problem is with such measurement is: You just built a temperature sensor, that will accurately tell you, what is the temperature in the room. If not the reference, then your multimeter.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 07, 2013, 10:32:48 pm
content: Quote from: NANDBlog on November 07, 2013, 09:26:14 pmTo eliminate any effect from the LEVEL of temperature, all you have to do is to take your daily measurements at around the same time when the room temperature is the same as yesterday and the the day before and ...This method fails first when your chosen temp is not in the daily span of the room anymore. In comes heaters and aircon. They might change the LEVEL of humidity and so it goes again ...What Andreas talks about over is (quasi)permanent effects of the HISTORY OF THE CHANGE IN THE LEVEL of temperature and maybe more. This is called hysteresisThen you may have DEVICE CHARACTERISTIC changes that can come with time, after soldering, expansion of package, application of too high voltage, physical damage to the package etc...Some of these things you can correct for on the measurement level. Some can be conditioned away by treatment of the chip (removal of hysteresis), some are permanent and you know why they came (you stepped on the chip), and some are unexplainable. All this is OK if you look at it from a scientific point of view. Some things can be accounted for and adjusted when you present your results - other things are just unexpected and unexplainable shifts. And you just say so. No need to try to hide them or smooth them out.I will notreadcomment on your blog link - in stead I'll give everyone that is really interested the following challenge:1/ Try to find an old datasheet or whatever where it is claimed 0.2 ppm long time drift for an unsupported chip. Then ask yourself: What the h... were they thinking (or not thinking) when they wrote it.2/ Readhttp://cds.linear.com/docs/en/design-note/dn229f.pdfand ask youself why did LT react as they did.3/ Readhttp://www.edn.com/design/analog/4363748/Voltage-references-hold-steadyand ask yourself how could a supposed electronic engineering journalist/writer print the last table of the article.4/ Readhttp://www.edn.com/electronics-blogs/anablog/4311058/Voltage-reference-drift-considerationsand ask yourself why did the late Mr. Pease ofLTCNational Semiconductor react as he did.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 08, 2013, 01:38:20 am
content: Well - I'll start measuring today without touching anything for a week or more. But in order to let everyone know what my best equipment is - here is a video. Do the math yourself.I have some other things to do, and my internet is crap, so I don't know when I get the chance to post. Anyways - the ceramic AD587LQ 10V ref from gellerlabs.com has been within 10.00001 and 10.00014 for all temps in my 'lab room' and all cables I have used since I bought it some 3-4 months ago. So the composite error from ref and DMM is imo low enough for this practical experiment. Nice meter and nice board - well behaved ..

author: bingo600
author_rank: Super Contributor
timestamp: November 08, 2013, 07:07:37 pm
content: Your 34401A is blinking quite fast in the "Aquisition asterisk" , are you sure you have set it to 100-NPLC & 6-digit slow (Geller reading)?My 34401A does blink with 2Hz (here in 50Hz line freq land ... EU)Edit :Right now i have 2 Geller's active (since april).One on a Keithley 2015 Cal'ed May-2011 - (Geller SVR) , and one on a 3457A Cal'ed 40 days ago -(Geller SVR-T)I have noticed that the SVR-T on the 3457A is drifting a lot more than the SVR on the 2015 , when temperature changes in my lab (22.4 to 26.7 degrees).If i swap meters on the SVT & SVR-T , then the SVR-T is spot on on the 2015 , and the SVR is actually also close to spot on , on the 2015.I mean on the 3457A i see 9.99998 to 10.00012 within the range.On the Keithley i see 9.99998 to 10.00002 within the temp range.This leads me to think that the 3457A is a lot more sensitive to temperature changes , than the K-2015 is.Has anyone noticed that the 3457A is very sensitive to temperature changes ?I might have to do the excercise with my 34401A instead of the 3457A , t see if they still fiffer/Bingo

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 09, 2013, 01:57:41 am
content: Quote from: bingo600 on November 08, 2013, 07:07:37 pmTo be honest, I never thought of it. I use FAST 6.5 Digit because I want averages and max-min on the external display. But I changed to SLOW.This video - [#06] - was supposed to be the first "flawless" measurement. Note that GE shows 10.00006 which is a correct done measurement. Why it doesn't read 10.00000 is everyone's guess - drifted ref or error in DMM or both. Notice that WH3 shows 2.50000 Volt.NB! In all videos from now on the measuring cycle will be:GE, WH4, WH3, WH2, WH1, GR4, GR3, GR2, GR1, VS, GE(where WH(ite), GR(een), GE gellerlabs.com, VS voltagestandard.com).Why is WH3 suddenly so "good"? The answer is the common/ground lead to the DMM (the black crocodile clip to the right) - I forgot it at the 'GND Sense' of GE, and the voltage loss introduced by ground cables happened to reduce the measured voltage so that it shows 5.0V exactly.I have made a new video (due to my bad internet it will take some hours to upload it). I post this one to illustrate Andreas' point from an earlier post. Also if I am going to wait until everything is "perfect" I will never get anywhere. I am in here to err and correct - the only way to learn ...

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 09, 2013, 07:52:00 am
content: Unless there is something seriously flawed, I will not change this setup. Notice that WH3 is up from 2.50000 to 2.50012 due to change of ground reference. So for ALL refs - including GE - the display does NOT show ref voltage output (but Vout+Vdiff-chipgroundpin-to-starground). The bias error are in order 100uV.Of course I could solve this bias 'problem' for all refs by moving 2 probes for every measurement, but I will not. The voltage levels are irrelevant for tracing changes (as long as the ground lead currents are constant). Given that I will do this measurements for more than a month, I will reduce the possibility for error by not changing anything and just move the red test clip lead in the clockwise circle GE, WH4, WH3, WH2, WH1, GR4, GR3, GR2, GR1, VS, GE. I cannot MUX the grounds, but if I get 10 DPDT relays, I might do Vout/GND sense and automate the measurements.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 11, 2013, 06:13:04 pm
content: Forgot to say - using 6.5 Digit SLOW mode on the 34401A was a bad idea for this setup, so I am back to 6.5 FAST.I have tried to measure the unbiased "real" voltages on the output pins of the ICs (Vout sense and GND sense - no currents flowing). The chips are very small and I used a pair of Agilent modern probes that I got from Agilent as a thank you for some reports of errors in some documents. I don't like them. Too small and flimsy. Anyway - this is the best I will do.So I am back to the "standard" loop GE, WH4, WH3, WH2, WH1, GR4, GR3, GR2, GR1, VS, GE by moving a single test wire - the red crocodile Vin for the the Agilent 34401A.I am too lazy to take notes, so I will continue to spam YT with videos. At least the links take no server storage here on this forum ...

author: tszaboo
author_rank: Super Contributor
timestamp: November 11, 2013, 06:57:28 pm
content: Quote from: quantumvolt on November 11, 2013, 06:13:04 pmHow dare you! Those are the best probes I can wish for! Absolutely love the "contact" I can feel when the spring kicks in, they are small, so I can measure two things with one hand! They are awesome.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 13, 2013, 01:30:03 am
content: Quote from: NANDBlog on November 11, 2013, 06:57:28 pmSorry.Shame on me.---ooo---More voltage video notes. Unless you want to know what the refs read the last 2 measurements - just ignore them. I am too lazy to write, so it is my notes ...

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: November 15, 2013, 09:55:41 pm
content: Quote from: Andreas on November 07, 2013, 06:12:23 amThat was a wonderful chart, thank you for sharing!Do you have any thoughts on how power cycling affects stability of these? Certainly high temperature stabilized references will suffer from cooling and reheating. But for room temperature references, is it better or worse to turn them off when not in use? How about the reference inside my bench DMMs (which presumably warm up a little?) This is one of the experiments I was considering conducting if I built my own array of references.

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 08:19:05 am
content: I leave mine powered on all the time, and it will only add about $1 to the bill over a year so no worse than any always on load. To compensate I unplugged the TV set and have not used it for the last few months.

author: Stonent
author_rank: Super Contributor
timestamp: November 16, 2013, 09:58:39 am
content: Quote from: SeanB on November 16, 2013, 08:19:05 amYou could fly to the moon on that much electricity!

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2013, 10:20:33 am
content: I could, it will just take a few million years to get the potential well energy differential needed from this though.

author: Andreas
author_rank: Super Contributor
timestamp: November 17, 2013, 06:57:38 am
content: Quote from: Galaxyrise on November 15, 2013, 09:55:41 pmHello,on precision references power cycling usually has little effect on stability.Voltage should be restored within 1ppm after 15-30 min power up time.Perhaps there is some (small) influence on ageing speed.And the behaviour depends on many factors:- Humidity sensidivity of the package.- Lead frame (copper or covar).- viscosity of the die attach (usually a silver filled epoxy)One reference that I have found to be unstable on power cycling is theISL21009BFB850. A low power low noise FGA reference.After a short voltage interruption the reference starts some 100uV lowerand needs some days to fully restore to the final value.Note: the behaviour is well within the datasheet accuracy specs.But you cannot get much better than this with calibration.With best regardsAndreas

author: chrome
author_rank: Regular Contributor
timestamp: November 17, 2013, 04:34:11 pm
content: Won't desoldering these IC's not ruin this burn in?

author: dannyf
author_rank: Super Contributor
timestamp: November 17, 2013, 04:56:27 pm
content: QuoteIs those chips were so sensitive to burn in, wouldn't that render them useless in the real world?

author: SeanB
author_rank: Super Contributor
timestamp: November 17, 2013, 05:01:29 pm
content: You normally solder them in once, then power them in a burn in fixture for a while to get most of the initial drift out. After that they will be stable enough. Desolder them though and you will start off somewhere between what they currently are and what they did as new drift wise though.

author: captbilly
author_rank: Newbie
timestamp: November 19, 2013, 05:35:05 am
content: Remember that the Agilent 34401a (I think that is what you are using) also has a temperature coefficient, as do your leads and connections (they all form thermocouples that will generate significant voltages), so you can't necessarily attribute all the voltage difference to the reference. In fact it is even possible that all the voltage difference you are seeing, when measuring at one time vs another, is due to chanages in the meter or leads or solder joints or... When trying to get down to PPM voltage accuracy there are all sorts of possible error sources. Even the best meters in the business will not give PPM accuracy or stability (over temperature or time. You certainly cannot hold the test leads in your hand and expect to get anywhere near PPM stability or accuracy (your hand will warm the leads and cause them to behave as thermocouples). The voltage of the reference will also change due to the input voltage changing (the change will be in the PPM/volt of input voltage change range). The voltage of the reference will also change due to changes in stress on the package as you touch the leads with your probe or due to the perf board swelling from humidity (can be 10s of PPM).The point being that without some additional care being used in your test setup it will be very hard to figure out what the cause of the voltage drift is.Quote from: quantumvolt on November 05, 2013, 08:51:18 am

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 20, 2013, 01:45:55 am
content: Thank you for your post. Although most of your points are valid in one context or another, many of them do imo not apply here.The measurements I do are not aimed at determining "accuracy" with any precision. My goal is to detect long time drift. This is quite a simple task. The set up I use is not - except from the dust falling on it - changed at all, and the temperature (as read by a crude fleabay thermometer) is recorded.So in a sense the fixed errors in my setup doesn't matter. I am out looking for long time permanent changes. By keeping the fixture fixed (pun), I eliminate most variable errors. Hence - any measured changes probably come from the DUT.This forum has quite a lot of knowledgeable people. See for instance the thread on 'LTZ1000'. I think I have learned enough from them to be able to estimate what must be attributed to the rig, the instruments, the measurement procedure etc. - and what is a real measured change in the measured attribute.I enclose a small video with a Processing sketch that lets me supervise these refs hands-off for intervals from second to days. Any change that cannot be attributed to the environment is probably a characteristic of the tested device.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 21, 2013, 07:04:15 am
content: I have had a feeling lately that these refs are quite stable. Today I checked measurements against 2 weeks ago. All 8 refs read the same (except from some cases that are 1 digit off on the LSD. This is not significant - it falls within the spec error of the 34401A).So while still powered for months to come - I will not report so frequently on the refs (unless something special happens).The refs seem to be very good indeed.Appr. 2 weeks ago:Today:

author: blackdog
author_rank: Frequent Contributor
timestamp: November 21, 2013, 08:26:01 pm
content: Hi quantumvolt,May i also play ;-)I made a test setup of 4x MAX6126-AASA 5V reference.Thisa is not the final setup, just for testing, i wanted to see how much noise i get, with 4 Reference's parallel. (0,5 times)It is a in a 30KHz BW about 4,5uV RMS.Datasheet of the MAX6126...First the schematic i used for this test.I placed the 4 Refs "Manhatten Style" in a small steel box.This is a picture of the open box, the Ref's are floating, it is easy to remove them and place them in an small oven.The coax cable goes to the multimeter.This picture shows the low noise of the for References, time 2,5 Minutes and 4,5uVPP maxAnd now a 10 minutes measurement, 5,5uVPPThis is the display of the "Audio Precision" Analyser bandwith <10H - 30Khz.This scoop picture is the output of the Analyzer, ignore the 50mV setting of channel-4.The Analysor is autoranging, this picture is just for a impression how the noise looks...Later i wil place more pictures :-)Kind regartsBlackdog

author: Andreas
author_rank: Super Contributor
timestamp: November 21, 2013, 08:58:40 pm
content: Quote from: quantumvolt on November 21, 2013, 07:04:15 amIm still waiting for a graph over time (drift in ppm over days) from your side so that I can compare it to the ADR4550 ageing.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 22, 2013, 10:56:27 pm
content: @blackdog Nice work. As usual you just don't do it - you do it thoroughly. I have seen your power supply projects on the Dutch forum. Very good. You use steel, copper, aluminum and BNC. I am more of a plastic, tape and banana guy@ Andreas. A diagram will come in the first days of December (appr. 500 hours). I will also comment on tempco, noise and some small level-shifts that appears randomly. When I say that some of the ADR441 refs seem to be "very good", I do not mean super stable and ultra low noise and tempco. I mean "quite good and usable - and seeming stable to around 10-20 uV (4-8 ppm for 2.5 V) - which is the best I can measure with 5 decimal digits." I will try to use the Processing Scatter-Plot shown in the video over to estimate tempco, p-p noise and document the shifts. But in general - I can say that a few of the refs have shown little or no permanent long time drift at all in the two weeks that they have been powered in the fixed (unshielded plastic) rig.

author: bingo600
author_rank: Super Contributor
timestamp: November 23, 2013, 11:01:35 am
content: Quote from: blackdog on November 21, 2013, 08:26:01 pmNice setupI have a lot of MAX6198-AESA (4.096v) , it seems they are not as good as your MAX6126.But if i want to make the same same setup , for testing should i then use 1nF as the output cap ?The DS says : Max 35uA supply , and stable with up to 2.2nF capacitive load ?I have a lot of 100nF , and prob. also some 10nF , but i'm not sure i have 1nF in the drawer.Can i use those or ... Should/must i use 1nF ?I'm an analog "noob" bit this seems like fun to try , and i have 100+ of those refs (*Bay offer)MAX6198 DS:http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf/Bingo****** Somewhat off topic , but related ***********Btw: What are you guyzz using as PSUs ?? .... a DIY ?I had a lot of trouble with a 18v wallwart switcher , a 7815 , and a gelller 10v-ref.Where there were quite a lot of switching noise in the 10v output.I had significantly better results using a used Cisco Router 18v switcher , where i (thanx to advices from my EE friend kkp) could somewhat "tame" the noise connecting the 18v input via 1uH to the 7815 input and then 2x220nF across the 7815 input legs , and 220nF on output. But the Cisco switcher gets "quite" hot even just feeding the geller-ref , so it's burning a lot of 24/7 wattage.So later switched to a HP E3610A@15v , to be on the safe side.I'd like to free the E3610A but not for the unit , as i also have a TTI PL-310 and 2x PL-154 witch i consider low-noise.But more to get a lower 24/7 power usage if possible.If anyone has a nice "easy" low noise DIY schematic for those few ma's .. i'm all ears.I have been considering using a real trafo "gasp" ....

author: Andreas
author_rank: Super Contributor
timestamp: November 23, 2013, 04:16:27 pm
content: Quote from: bingo600 on November 23, 2013, 11:01:35 amHello,I am using either 9V NiMH blocks or 8-12 AAA NiMH cells depending on needed input voltage on the references.The batteries are charged when no measurement is active.The input voltage is usually stabilized by a low noise LT1763 voltage regulator to either 14V, 9.35V or 10.5V depending on the minimum input voltage needed by the reference for a good PSRR.If you MAX61xx datasheet mentions that a maximum of 2.2nF is allowed then the output will oscillate probably with larger loads. Perhaps you can use larger capacitors with a additional "boucherot" or snubber cirquit. A R/C combination additionally placed at the output like recommended in the ISL21009 datasheet. (figure 58).With best regardsAndreas

author: SeanB
author_rank: Super Contributor
timestamp: November 23, 2013, 08:52:41 pm
content: I recycled an old phone wall wart ( Siemens one IIRC) that had a pair of 9VAC secondaries ( labelled 6VAC and 8VAC but identical windings) that I put in series and used the existing bridge rectifier there and upgraded the capacitor to a 1000uF 35v unit. This then fed a 7815 regulator inside the case, and then the lead to the VR was the original flat phone cord hard soldered both sides. Regulator had 100n each side and 100uF on the output, with a single green LED to show power on. Voltage regulator just has the AD581KH on a board, with an input LC filter ( used coil from a SMPS and a 100uF capacitor) and a 10uF 35V tantalum on input and output of the regulator. A second LED to show power and that was it, all in small wall wart cases recycled for the purpose.

author: bingo600
author_rank: Super Contributor
timestamp: November 23, 2013, 11:33:35 pm
content: Thanx Andreas & SeanAndreas how do you get those odd voltages out of the LT1763 ?I have some MIC-2940A-5 LDO's would they be ok (stability or noise wise) for 5v ,the MAX6198 (4.096 volt) only needs +.2v to regulate.http://www.micrel.com/_PDF/mic2940.pdfA whole bookhttp://www.micrel.com/_PDF/other/LDOBk_ds.pdfSeanQuote from: SeanB on November 23, 2013, 08:52:41 pmWas that a switcher or an IronCore , i'd guess Iron but ?/Bingo

author: SeanB
author_rank: Super Contributor
timestamp: November 24, 2013, 05:01:20 am
content: Mains frequency transformer. Luckily the one in a separate case, the current versions pot the whole transformer and lead with a moulded in Euro 2 pin plug to make the case, so you cannot open it without using a destructive disassembly. 9VAC at around 200mA max, happy with the 50mA load that is mostly the regulator and the 2 LED's. Separate cases both for convenience and to remove the voltage regulator from a source of heat from the transformer and regulator, as the transformer does run a little above ambient, the case is 11C above ambient at the moment.

author: Andreas
author_rank: Super Contributor
timestamp: November 24, 2013, 07:57:13 am
content: Quote from: bingo600 on November 23, 2013, 11:33:35 pmHello,I'm using the adjustable version of the regulator (LT1763CS8 without any other suffix).The output voltage is programmed by resistors. See page 15:http://cds.linear.com/docs/en/datasheet/1763fg.pdfFor the voltage regulator.Any regulator is better than none.It reduces at least drifts from input voltage changes by self heating of the reference.At least when the regulator is not placed directly near the reference.If you really need low noise depends on your application (depends on what you are doing).I am using usually integrating ADCs where the broadband noise plays no role.And at low frequencies the noise reduction of the reference is usually good.But the LT1763 has many advantages: low noise, low quiescent current and low drop.The only disadvantage is the low PSRR compared to other regulators.But since I use batteries this plays no role for me.I personally choose the input voltage of the reference near the optimum PSRR voltage.For the LTC6655 this is around 9.3VWith best regardsAndreas

author: bingo600
author_rank: Super Contributor
timestamp: November 24, 2013, 04:37:38 pm
content: Thanx Sean & Andreas.I have a few 2 x 9v PCB trafos rated for .3A i think per winding.Looks like i'll be using one of those , a bridge rectifier and 2 x 470uF 25v.And then just add a few Vreg's after.1 x 78151 x 78121 x MIC2940-51 x MIC2920-3.3/Bingo

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 01:11:38 am
content: I finally have a full day to document what has been going on until now. I start with one of my spam videos for todays measurementsI am impatient as usual and will post bit by bit as I try to make order out of the data mess.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 01:47:56 am
content: THE SETUPThe setup is all plastic and tape. No shielding. Power supply 5 volt is a wall wart with transformer followed by a 7805. The voltages are measured referenced to a common ground point (i.e. not the ground pin on the chip).This means that there are bias in the measurements - the numbers will include both the ref voltage and a small voltage over the ground supply cable (order 100 uV).This is just a constant (dependent on the length of the ground wire for each reference) and has no significance in measuring differences (drift). It saves me from moving the "minus" lead when measuring.The rig is untouched for more than two weeks - measurements are done by moving a single DMM input "plus" wire with a crocodile clip.The naming/measurement order is:GE, (green board to the right)WH4, WH3, WH2, WH1, (white board center - WH4 rightmost)GR4, GR3, GR2, GR1, (green board to the left - GR4 rightmost)VS, (green board behind GR1-4)GE(where WH(ite), GR(een), GE gellerlabs.com, VS voltagestandard.com).GE and VS were included as "checks".Edit - Bold.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 02:18:37 am
content: A MIDDLE OF THE ROAD EXAMPLE -GR4NB! It turns out that - for almost the same temperature - the 34401A reads consequently around 100 uV (4 ppm for 2.5 volt) higher after being powered an hour or more (don't know yet how long warm-up time it needs). This is not a big problem as long as I am not trying to document any measurement HISTORY (but it probably means that some of the measurements are a few ppm low). I am only concerned about long time shift trends. These will reveal themselves in the future.There are 15 measurement of GR4 since Nov (7 or) 8 (first day with fixed set up. A few days were not measured - and a few days were measured with "wrong" ground reference point, and are accordingly discarded. This doesn't matter for determining long time drift relative the first day of valid measurements. The refs will be followed at least until next year. Time enough ...GR4Nov 8-26, 15 measurementsVoltPPM total drift2.5002702.50026-42.5002702.50023-162.50025-82.50023-162.50021-242.50021-242.50022-202.50022-202.50024-122.50024-122.50025-82.5002702.50028+4There is no correction for temperature (ca. 27-30 degrees Celcius). The tempco will probably more or less drown in measurement errors. For now I am only looking for steady drift in one direction. Later I will estimate tempco using forced heating/cooling.

author: Andreas
author_rank: Super Contributor
timestamp: November 26, 2013, 05:34:26 am
content: Quote from: quantumvolt on November 26, 2013, 02:18:37 amThe 34401A needs at least 1 hour of warm up time to fullfill 6,5 digit specifications. (page 216 of user manual).For transfer accuracy it is a minimum of 2 hours of warm up time (page 217).A LM399 itself needs around 15-30 minutes until the heater of the reference reaches steady state with changes less than around 1 ppm of the output voltage.Since tempco is the largest measurement error I would try to calibrate it out by regression analysis.If you would draw graphs with temperature and output voltage over time and output voltage over temperature you would see if there is any correlation.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 06:21:15 am
content: Thanks Andreas.May be I have become too sloppy. But at least there is room for improvement.I do have the recorded temperatures, and will put them in the table/graph next time (in two weeks time).In any case, this points out that these data must be taken for what they are. They contain errors from:- bias- cold instrument- tempco- EMF*- more ...(*I just came back from lunch and can see from the door that when I enter the room and come closer to the setup then 2 meter, the reading goes up with one last digit (10 uV).)However - since there is drift in two directions, it is anyones guess where the GR4 will be in 2 weeks.Anyway - my next table will be something like this:TempVoltuV tot.ch.Temp %ch.PPM tot.ch.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 06:57:17 am
content: NB! The ref I am working with is GR4 - not GR1. I will edit the post over.A 3 minutes plot of the RS232 data stream from the Agilent 34401A. The number "P-P" is (Max-Min). According to the datasheet this ref has noise 1.2uV 1-10 Hz and around 50 uV 1-10 kHz. So a value of around 15 uV peak-to-peak seems reasonable.

author: Andreas
author_rank: Super Contributor
timestamp: November 26, 2013, 07:21:45 am
content: Quote from: quantumvolt on November 26, 2013, 06:21:15 amHello,that´s why I use a metal plate as base for the DUT´s and the instrument on my hobby desk.And perhaps you have to put your mobile out of your pocket when measuring.To keep air currents away from measurement setup I use clothes over the cirquits.But this needs automated measurement.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 07:51:14 am
content: Yep - it is all in my plans. But I am in a lazy mood. I am working with the AMPREF / REFAMP schematic and a PMBus Automated Testbed (I2C programmable test rig - big fun).Here is 45 minutes of the same stuff. As I do not know how much noise is smoothed out by averaging in the DMM, I will use the LTC2400 for my next noise estimate.Another day

author: captbilly
author_rank: Newbie
timestamp: November 26, 2013, 08:35:11 am
content: The 34401a is not 6.5 digit accurate. The specs from Agilent are: on the 10 volt scale, for 24 hours, error is 15ppm of the reading plus 4ppm of the 10 volt range. If your reference is 2.5 volts your error could be as much as 15ppm plus 16ppm ((10/2.5)x4), which is about 31ppm/0.000031 (about 4.5 digits). The 34401a is a great meter, I have had one for 20 years, but the 6.5 digits are only useful for seeing small changes over very short time frames, not over hours. In fact, if you check the longer term specs on the 34401a you will see that the error over 3 months grows to 40ppm, and then 55ppm over a year (and all these errors are assuming no more than a 1 degree C variation in ambient temperature. These are great specs but they do not allow us to claim that we can differentiate between a few ppm drift in the reference being tested and a few ppm drift in the meter itself.Even the industry standard Agilent 3458a is generally " only" accurate to 8ppm per year (there is an option to get that to 4ppm per year). A Fluke 734a voltage standard can get down to 0.3ppm for a month, but that requires that the reference is never powered down, including when it is shipped to you from Fluke (this is why it has a battery), that you use special low leakage test leads, and that you do not take a reading for several minutes after touching the leads (or any other part of the test).Quote from: Andreas on November 26, 2013, 05:34:26 am

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 08:53:50 am
content: Hi again captbilly.Happy to see you again. Hope you come back more often.I agree with much of what you are saying. In fact - if you read my thread on the LTC2400 / LTC1655, you will see that I state that I have no "1 ppm"-dreams whatsoever.These refs are treated honestly. I use what I have with a somewhat laidback attitude because my ONLY goal is to see if they are reasonably stable. If the DMM was going roller-coaster, all refs would reflect that.I like the ADR441. So be sure they will be treated decently in my quasi-reporting.Are you from ADI?

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 26, 2013, 09:53:40 am
content: I have found an error: I write over: "NB! It turns out that - for almost the same temperature - the 34401A reads consequently around 100 uV (4 ppm for 2.5 volt) higher after being powered an hour or more (don't know yet how long warm-up time it needs)." Shall be 10 uV - not 100.Also - the noise numbers from the datasheet given over should be: ca. 1.2 uV for 0.1-10 Hz and ca. 45 uV for 10 Hz - 10 kHz.captbilly writes: "If your reference is 2.5 volts your error could be as much as 15ppm plus 16ppm ((10/2.5)x4), which is about 31ppm/0.000031 (about 4.5 digits)."In my opinion it shall be (15+(4x10))=55. In general - the FS error is independent of the actual measurement level (in this case 2.5 volt nominal).

author: blackdog
author_rank: Frequent Contributor
timestamp: November 26, 2013, 08:06:33 pm
content: Hi,Last week I promised to show more pictures of my MAX6126 reference.This is a picture of the "Trend Plot" function on de TEK DMM4050 multimeter, almost 5 day of measurement time.it is not a straight line, this is due to the temperature changes in my lab, about 5C Delta.You can see thetrent is upwards an now about 10uV above the zero setting 5 day's ago.Now only 4 days measured with the HP 34401A DMM,And now some pictures of the oven i'am building for the references.The test setup, LM10 controler chip, 10W ceramic resistor, and a thin piece of board glued on both sides.The temperatuur is around 39CDuring my evening walk, thinking of Voltage References, I saw this beautiful picture of Amsterdam, and i like to share it with you :-)This is the resistor i use for my oven.Schematic of the oven controler.If you guys want to see more, go to this Dutch forum and use google translate.http://www.circuitsonline.net/forum/view/107437/1Kind regarts,Blackdog

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 27, 2013, 06:16:56 pm
content: Good work, blackdog. I like your "solid state" work. Sometimes I am fed up with coroplast, glue and tape, and also want to make some more rubust stuff. So I have ordered 20 copper clad boards.Amsterdam is beautiful. The picture reminds me of my younger days - Amsterdam, Paris and Budapest have (in different points in time) been 'home' to me - many decades ago. But after more than 10 years in Asia it is all but memories ...

author: blackdog
author_rank: Frequent Contributor
timestamp: November 27, 2013, 08:22:06 pm
content: Hi quantumvolt,Thank you!I can't program a Arduino ore a PIC processor, we can all have a kind of trick where we are good at :-)But it's good to hear, that you now have ordered printed circuit boards!I Hope yo make a nice project of de 34401 logger.Maybe you can spent a holiday in Europe?Kind regartsBlackdog

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 27, 2013, 10:34:28 pm
content: Europa Barbarorumis my beloved birthplace. But I cant stand the F.ing cold and snow. So I left a long time a go.If you mean make a "project thread" of the DMM logger here on the forum, I can do that. All people need is an Arduino, a RS232 cable and my bad but working code. Performance guaranteed (Arduino/Processing is like useful Lego - you don't need much knowledge to get results).Also - I am now researching a "real" noise logger - a High Speed Low Noise SAR ADC "Crest Factor and Noise Power Estimator" in software. I need help - so I can do both things in the same thread. If anyone is interested...

author: Andreas
author_rank: Super Contributor
timestamp: November 28, 2013, 05:47:20 am
content: Quote from: quantumvolt on November 27, 2013, 10:34:28 pmWhat do you really want to do with it?Measure which kind of noise (0.1 - 10Hz 1/f noise or 10Hz - 1kHz or 10Hz-100kHz broadband noise?)Which amplitude?High speed and low noise exclude each other.For good reasons usually bandwidth limited amplifiers are used and the output is fed into a true rms voltmeter (rms noise) or oscilloscope (pp-noise).With best regardsAndreas

author: Harvs
author_rank: Super Contributor
timestamp: November 28, 2013, 05:59:32 am
content: QuoteI'm not really sure what you had in mind. If there's something I can include in the tablet app to help out let me know.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 28, 2013, 07:42:46 pm
content: @ Andreas. "High speed and low noise exclude each other."Well - it's kind of relative - as is all use of language. There is nothing contradictory when they write:"The LTC®2378-20 is a low noise, low power, high speed 20-bit successive approximation register (SAR) ADC.""The MAX11190 is a 4-channel, dual, multiplexed, 12-bit, compact, high-speed, low-power, successive approximation analog-to-digital converter (ADC). ... 3Msps Conversion Rate. Simultaneous Sampling. Low-Noise, 72dB SNR. "(There are more examples on the web)I guess some people would find the LTC chip at 1 Msps and 100 db SNR kind of fast and silent. Anyway - the description of the ADC's are not my words ...@ HarvsI want to make a 10-16 Bit digitizer/plotter/scope (1 sps- 100 ksps) as desribed on page 5 and 16 here:http://cp.literature.agilent.com/litweb/pdf/5989-6319EN.pdf. I' will use 3 ADCs - the two over and the LTC2400. Combined with a LT1970 based 4-Quadrant DC Source (http://www.edn.com/design/analog/4332968/Four-quadrant-power-supply-provides-any-polarity-voltage-and-currentit will be my new long time DC toy. I have even bought a cheap Karaoke-box with "a million" pots and sockets and ripped out everything except the big toroid transformer. So then I have a 19 inches rack-style case. The software and display will be on an Arduino DUE (around 80 Mhz).I guess I'll better ask in your tablet thread when the time comes. My intention over was to find out if anyone wanted the simple plotter used in this thread.---ooo---DC-Toy at 10 kilodollar ...

author: Harvs
author_rank: Super Contributor
timestamp: November 28, 2013, 11:02:11 pm
content: That would be a very nice tool to have on the bench...

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 30, 2013, 12:24:06 am
content: The eight ADR441 refs have now been under power in an unchanged setup for more than 500 hours. The setup, the meaurement method and the measuring instrument(s) have limitations and errors. These are described in earlier posts.I will sum up a bit of the data I have. Half of the refs will continue in the same rig with the same power supply 5 V. The other half will first be powered by 9 V to see what effect (if any) this will introduce. After a week or so they will get a round of heat and cooling to see if any ("hysteresis") permanent changes occur.I have decided that it is a waste of time to put a lot of work into spreadsheet plotting, analysis and regression. The thermometer used has a listed accuray +-2% (imo not trustable), and seems to have a resolution of 0.3 degrees Celsius. And it is not even monotonic (I have seen several times it goes from 29.4 to 29.1 to 29.7 degrees Celsius on its way up from 29 to 30)). With a span of 27-30 degrees Celsius in room temperature, it is meaningless to make detailed analysis of variation "due to temperature changes".I also am lazy and a bit bored (other projects are waiting). But in general it is my view that these refs are quite good all round refs, have high initial accuracy, moderate to low noise and short time drift (minutes to hours), and are long time "stable" up to now. They have - as is stated in the datasheet (and as the max-min values measured over a night will show) - a moderate to low tempco. It all depends on what you mean by these words - what is good stability for a 7805 regulator is a disaster for a DMM.I'll leave it to people to make up their own opinion. Even if this thread is lacking a lot, there is enough information here - combined with the datasheet - to somehow see what they get from these refs. I myself have wasted 50 USD on so called "reference boards" that have behaved worse than these chips.My main purpose with this thread is fulfilled to some extent. I now know what I will do different if I ever do this again.I'll keep them powered and "monitored" until early next year. But I won't put too much energy into it. The things I have at this "500 hours summary" will follow in smaller posts below. I will also - as I said in the beginning - give links to the papers I have found containing information relevant for voltage reference "burn-in and ageing".

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 30, 2013, 01:50:43 am
content: I have overnight Max-Min readings for two of the refs (note that the datasheet temperature coefficient is given as 10 ppm/degC):GR4, 26/11 PM 30.5 degC - 27/11 AM 28.2 degC: Min 2.500267, Max 2.500295, Avg. 2.50028. Span 28 uV or 11 ppm for temp change 2.3 degC - i.e. a tempco estimate around 5.5 ppm/degC.WH3, 29/11 PM 29.7 degC - 30/11 AM 27.6 degC: Min 2.500116, Max 2.500153, Avg. 2.500134. Span 37 uV or 14.8 ppm for temp change 2.1 degC - i.e. a tempco estimate around 7.5 ppm/degC.Both refs (probably all) are better than the published specification (hardly surprising - the specs are given so that they cover most of the "worst" cases), so I will not dwell more on this.The problem that arises after you have bought more and more, better and better refs over a period of months or longer (I have at least 20-30 "quality" refs now - most of them not yet powered), is that good refs like these are not "good enough" anymore ...

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 30, 2013, 02:51:55 am
content: Since I will change supply for WH 1-4 from 5 volt to 9 volt, I list all data I have from Nov 8 (or 9) until today:WH1 : 2.50070, 69, 70, 69, 66, 65, 63, 63, 65, 65, 66, 66, 69, 68, 67, 68, 68, 70, 69, 68WH2 : 2.50015, 14, 15, 13, 10, 09, 09, 10, 14, 11, 12, 12, 15, 14 ,11, 14, 14, 15, 16, 15WH3 : 2.50012, 11, 11, 10, 09, 07, 07, 08, 10, 09, 09, 09, 13, 11, 08, 12, 11, 13, 13, 13WH4 : 2.50068, 67, 66, 64, 62, 62, 61, 64, 64, 65, 64, 69, 67, 66, 67, 67, 67, 68, 68, 69There is a "dip" in the readings of all all four a week into the data. I don't know what it is (it is probably not temperature, since there are almost similar readings for 27.5 and 29.1 degC).Anyway - even without graphing, it doesn't take a statistician to see that one cannot reasonably claim any drift trend in these data (more than 500 hours). To be honest - I do not expect any future change in the refs. What has not been revealed in 500 hours is probably not there. In this sense this experiment is probably over. The rest is a waste of time. But I said 1000 hours and will do 1000 hours.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: November 30, 2013, 03:37:34 am
content: Links:A graph with asymptotic stabilization after several thousand hours "ageing"http://www.ti.com.cn/cn/lit/an/slyt183/slyt183.pdfBurn-in 4 weeks (672 hours)http://cds.linear.com/docs/en/application-note/an82f.pdf"Short period" burn-in and calibration after 200 hourshttp://www.analog.com/static/imported-files/application_notes/AN-713.pdfGeneral tutorial (TI), mentions 1000 hours "limit"http://www.ti.com/lit/an/snva602/snva602.pdfBurn-in 1 week (168 hours)http://www.edn.com/contenteetimes/documents/schweber/c0955/c0955-ch35b.pdfGeneral tutorial about (mostly ADI) refshttp://www.analog.com/static/imported-files/tutorials/MT-087.pdfAbout tempco etc.http://www.maximintegrated.com/app-notes/index.mvp/id/4419I have more, but these gives most of what I have found of information.Please post other resources here.I'll take a break to work with other stuff, but measurements will continue.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 05, 2013, 02:58:39 am
content: Quote from: quantumvolt on November 30, 2013, 02:51:55 amNB! Applies to WH1-4, not GR1-4 (they will run on 5 Volt until next year).I changed from 5 to 8 Volt on the same DC transformer based linear 3 pin regulator power supply Dec. 1. The changes in output from WH1-4 are:WH1 : 2.50075, 73, 71, 73WH2 : 2.50019, 19, 18, 17WH3 : 2.50017, 15, 16, 16WH4 : 2.50073, 73, 71, 72The first 4 measurements - taken just a few minutes after the change of supply voltage - shows that all 4 refs increased with appr. 40-50 uV for an increase in supply voltage of 3 (8-5) Volt. This is around 15 uV/V or 6 ppm. The datasheet says 10 ppm, so this change is within spec.- - - 0 0 0 - - -I have experimented with some more noise estimation. This is somewhat difficult because of the very low noise level, unclear definitions of what is measured and lack of proper instruments.The first photo shows several minutes from the 34401A giving appr. 20 uV p-p.The second photo is LTC2400/QuikEval indicating around 20 ppm p-p or ca. 4 ppm RMS. For 2.5 V this (20 ppm) is some 50 uV p-p, which is almost the same as the 45 uV indicated in the datasheet.The difference (between 20 and 50) might be averaging in the 34401A. No thought is given to frequency ranges 0.1-10 Hz and 10 Hz-10 kHz which is the division used in the datasheet. This will be one of my projects next year: DIY Noise Measuring.The last photo shows the LTC2400 with shorted input - noise around 6 ppm p-p or just under 1 ppm RMS.

author: captbilly
author_rank: Newbie
timestamp: December 09, 2013, 11:29:41 pm
content: Quote from: quantumvolt on November 26, 2013, 09:53:40 amThanks for looking over my calculations. Now I am having one of those confused moments (where a simple concept suddenly seems very complicated). My calc on the error of the meter was: the spec on full scale error is 15PPM, so any reading on the 10 volt scale starts with 15PPM error. Then there is a 4PPM error, of the actual measured value... hold on, let me try this another way. 15PPM of full scale equals 150uv (15ppm x 10.0 volts) then we have a 4ppm of the reading error which equals 10uv (4ppm x 2.5 volts), so the total error is 160uv, which over the 2.5 volt reference value, is 64ppm (0.000160 / 2.5). Does this make sense to anyone reading this? I think I did the calc wrong in my first post but I think 64ppm is correct.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 10, 2013, 12:44:16 am
content: No, imo it is not correct.According tohttp://cp.literature.agilent.com/litweb/pdf/5968-0162EN.pdfthe accuracy is 0.0015%  "of reading" plus 0.0004%  "of range".So the max error in uV is:(15/10^6)*2.5V + (4/10^6)*10V = 37.5 uV + 40 uV = 77.5 uVCheck:For 10 V this is 7.75 ppm.For 2.5 V it is 4*7.75 = 31 ppm which is composed of 15 ppm of reading 2.5V (i.e. 37.5 uV) plus 16 ppm of reading 2.5v (i.e. 40 uV) [4ppm of 10V FS rangeconvertedto 16ppm of reading 2.5).So your first number turns imo out to be right. I added ppms of different bases and was wrong. (EDIT: Double check: For 0/2.5/5/7.5/10 V reading the max one-sided error should be 40/77.5/115/152.5/190 uV which is NA/31/23/20.33/19 ppm of reading. Hopefully we can agree on these numbers. And for 1 V measurement it should be 55 ppm of reading. Yes?Anyway - this is accuracy, a measure I do not use for measuring differences. The accuracy spec is set wide in order for (almost all of) the "worst"-error meters to give a measurement within the spec. But the bulk of the meters will fall within a few ppm.Hopefully (read certainly) the meter's stability/drift is significantly better than it's accuracy (for a properly working aged instrument in a stable environment). The very drift that took the instrument to the end of the spec range (or even out of calibration), diminishes over time. But sure - somebody please send me a 3458A and I'll redo all the measurements

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 11, 2013, 03:18:41 am
content: The 4x ADDR441 called WH1-4 have been a tour in the freezer (an old semi-open freezer in a fridge). As the pictures show they were battery powered for a few hours and ran on sub zero temperature. After thawing they climbed back to original voltage minus 10-20 uV - the battery had fallen from 8.5 to 4.6 Volt, so this reduction in ref voltage must be define as line regulation.After being hooked up to the usual supply for an hour they all (except one that is down 10 uV and one that is flickering up 10 uV) went back to the same values as before the measurement.Conclusion: No detectable change in ref voltage ("hysteresis").

author: Andreas
author_rank: Super Contributor
timestamp: December 12, 2013, 09:35:57 pm
content: Quote from: quantumvolt on December 11, 2013, 03:18:41 amHave I understood it right: you compare the voltage difference "before the cool down at 27.4 degrees" with "after cool down at 18.0 degrees". Not knowing the exact temperature of the reference (due to self heating).Resolution of your readings is 4 ppm. So if you get a difference of 10uV you cannot tell if it is 4 or 12 ppm since everey reading has 10uV uncertainity. Why do you not use the reading on the external RS232 display?Usually Hysteresis is measured at exact the same temperature (25 degrees) before and after. And usually the temperature excursion is in both directions. Either +/-25 degres around 25 degrees (i.e. 0 - 50 degrees) or over the whole specified temperature range of the reference.For hysteresis measurements I usually use a fan to equalize the temperature between reference and temperature sensor.For the ADR4550B I measure different hysteresis magnitudes for cold and warm excursions. So it would be interesting how the ADR441 behaves on 50 degree excursion.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 13, 2013, 11:36:36 pm
content: No, I do not compare 27/ 18 degC. The pictures are for illustrative purposes (or no purpose at all). The last picture shows the refs running inas beforeconditions (except from the LED).The 18 degC picture - as I can recall - shows the 'event' when I discovered that the battery was down to some 4.5 Volt, and I changed - as I write over - to the usual PSU. I compare Vref_before and Vref_after at the same line voltage and almost the same temperature.As I have stated before, I do not believe in 'exact' measurements anymore. If a setup is untouched (even to the position of the measuring leads), I'll accept short time comparative measurements at max resolution.I have two times stated that the refs will be givenbothheating and cooling. I do not believe that the 'hysteresis' test (which is no physical hysteresis - but just an observation of any 'permanent' change in reference voltage) must be performed in any special way. The warm excursion (using a soldering iron as heater) will come later.So my temporary conclusion should better be:No detectable change in ref voltage ("hysteresis") on a 50 uV level. [50 uV is chosen because it is 5x DMM resolution on 10 V range. 50 uV is 20 ppm for 2.5 V. So my intended statement is that there is no reason to believe that the refs do not comply with the datasheethttp://www.analog.com/static/imported-files/data_sheets/ADR440_441_443_444_445.pdfwhich states hysteresis 70ppm.From a practical point of view: No measurable (with the 34401A) significant change in voltage was detected after the cold excursion, or anytime later.--- ooo ---I am somewhat finished with this experiment. I will keep the white board for the heating experiment. If you PM me your address I will send you the refs on the green board.Imo these refs are very good robust all round refs. But it is time to move on. I will parallel 4 of them for my next experiment - a digitally controlled boxed fixture (fully automated, no touching of anything) with LTZ1000, LM399, AMPREF, 1N829A, LTC6655, ADR441 and many more (multiplexed measurement bus with relays).

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 20, 2013, 08:17:59 am
content: The heating or 'warm excursion' is done. Maximum chip package temperature for the several hours 'session' was a bit over 60 degC compared to normal room temp here now around 25 degC. It is 'winter' here in Thailand (as everywhere in the northern hemispere), so the usual almost daily measurements are not at 27-30 degC any longer, but at around 24-26 degC. This means that the average voltage output for all refs have shifted a few uV.Contrary to the cooling which seemingly did not generate any significant changes in any of the four refs, the heating seems to have done so for (WH3? and) WH4. The white board WH1-4 (picture in post over):Before (24 degC : 2.50075, 2.50019, 2.50017, 2.50073Heated, max val. : 2.50085, 2.50034, 2.50031, 2.50081After (26 degC): 2.50073, 2.50018, 2.50012, 2.50056It is impossible to measure at 24 degC after heating since the room is hotter at some 26 degC now in the afternoon. The last readings are just a few hours old, so things might change.More than 1000 hours have passed since first measurement. Power has been down just a few short times. I will wait a few days to see where the refs stabilize, and then sum up this experiment.

author: Joe Geller
author_rank: Contributor
timestamp: December 26, 2013, 01:08:04 am
content: This post was edited based on a closer inspection of the photo.quantumvolt: In the Nov. 7 picture (DSC01133s.jpg (137.52 kB, 600x450 - viewed 62 times.)) of the 10 V SVR board, the DMM Red lead is shown clipped to the SVR Vref+ output terminal.The DMM black lead is at a central common on the white plug board. The SVR power common terminal is connected via a black clip lead and wire to the same common terminal on the white plug board.With the DMM black lead on the side of the SVR power lead away from the SVR board (at the white plug board), the 10 Vref+ now includes the SVR board 10 V output plus the IR drop across the black lead that is powering the SVR board.The SVR board draws on the order of 3.3 mA. So, to get a 280 uV IR drop, all that is needed is 85 milliohms. That black jumper wire and clip lead and contact resistance might well be about 85 milliohms.The meter V+ lead should be on the Vref+ copper lug (as it is). The meter V- lead should be on the center lower common copper lug of the SVR board. There should be no other connections.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 26, 2013, 02:14:23 am
content: I know. Maybe it is unfair to use your board connected like this, but if you look at earlier posts I several times clearly state some variant of:The voltages are measured referenced to a common ground point (i.e. not the ground pin on the chip). This means that there are bias in the measurements. This is just a constant (dependent on the length of the ground wire for each reference) and has no significance in measuring differences (drift). It saves me from moving the "minus" lead when measuring.So for the record:A WARNING TO READERS: THIS THREAD IS ABOUT DIFFERENCE MEASUREMENTS (DRIFT). PLEASE DO NOT ASSIGN ANY MEANING TO ABSOLUTE MEASUREMENT VALUES. THEY CAN HAVE MEASUREMENT BIASERRORS IN ORDER OF 100 UV OR MORE. A FIXED COMMON GROUND IS CHOSEN TO MINIMIZE THE MANUAL INTERFERENCE WITH THE SETUP. IDEALLY ALL 10 CHANNELS (REFS) SHOULD HAVE BEEN MEASURED AT Vref_sense/Vgnd_sense WITH A DPDT RELAY SWITCH/MUX.I put in a "correct'' picture showing the four leads (the supply leads should have been somewhat more 'solid state' (thicker), but I guess they can deliver a few milliamps)

author: Joe Geller
author_rank: Contributor
timestamp: December 26, 2013, 02:38:31 am
content: Right, so there is at least 190 uV difference (+ 280uV from the picture - the present + 90uV). Plus if that is a SVR board, there can be an additional 50 uV / degree C from the original cal temperature (most were less, but still tens of uV / degree C).Send it back to me, and I will do a free calibration with an incoming value. Note your present bench temperature and the SVR reported cal temp, so we can make more sense of these numbers.That aside, I did not so much mean to be critical, but more to point out that while many of us are curious about TE junctions from all sorts of connections, significant IR drops can sneak in without warning. It takes very little R to add ppm error to a Vref board output, that is why we used 2 mil copper, even for the short runs. For HiZ measurements, a non-issue, but draw 5 mA, and low output R is critical.One problem with repeated relative measurements with this series power IR drop is that the IR drop can vary widely by how good the contact R is with the copper lug at any given time. For HiZ DMM measurements (10 Meg or literally the HiZ 1 or 10 Gig mode), the IR drop is a non-issue. That is why these types of DMM references can still work with a great variety of connections. Of course certain metals might give 10s of uV of differences, but that is another issue.I broke out the Ballantine micro ohmmeter to get a quick gut check. Here are two jumper leads, one with relatively heavy jumper wire, something like .035" (roughly 25 strands of .006" dia tinned copper wire) about 12 1/2" long with a strong alligator clip (30 milliOhms), the other having relatively fine wire about .02" dia (roughly 7 strands of .006" dia copper wire) with a somewhat less strong clip about 6" long (648 milliOhms!).12/26 Afternote - The very high value of the short lead seemed odd (inconsistent with the wire size, length and number of strands), so investigated a bit further. The new pic shows the short white lead was only crimped and not that well compared to the soldered connection to the heavier clip. I am sure it has probably been discussed here before, it is worth inspecting / repairing / soldering clip leads before making measurements. The earlier discussion remains the same, but check those clip leads! Thermoelectric voltages for the white clip are on the order of 2 uV to copper at room temperature. TE of the clips is another reason to always use same type grabbers / clips at the SVR copper lugs. That way same type TE junctions mostly cancel.You can do the same thing by measuring the current flow to the SVR board and the uV voltage drop from the center common point on the white board to the lower center copper lug on the SVR board then apply E/I.Of course, with a DMM connected to the heavy #18 copper lugs, the R of any wire that powers the SVR boards is almost a non-issue. It only needs to be heavy enough to carry 3 mA without dropping volts

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 26, 2013, 03:41:50 am
content: Thank you for your kind offer about calibration. But I prefer to wait, as I have learned the hard way that measurements on a uV scale is a very unforgiving task. I write in an earlier post (#86):As I have stated before, I do not believe in 'exact' measurements anymore. If a setup is untouched (even to the position of the measuring leads), I'll accept short time comparative measurements at max resolution.Hence I will build (still post #86) a shielded: ...digitally controlled boxed fixture (fully automated, no touching of anything) with LTZ1000, LM399, AMPREF, 1N829A, LTC6655, ADR441 and many more (multiplexed measurement bus with relays).When I am very "sure" that there is no (little/quite predictable) drift neither in DMM (I now have 3x 34970A with DMM also) nor in the refs, I am in for a calibration.I have mostly stated (please do a search on the forum) that I am very pleased with your ref board. Correctly used it fills my needs as the imo next best thing after a 3458A ref board (which I cannot afford).[EDIT - shortened / spelling errors - removed irrelevant video ]

author: Andreas
author_rank: Super Contributor
timestamp: December 27, 2013, 09:07:37 pm
content: Quote from: quantumvolt on December 26, 2013, 03:41:50 amMhm,is your 15V chinese wall wart that you are using a transformer + linear regulator or a switch mode supply?In the latter case I think its no wonder. I also have several hundred uV difference when using switch mode supplies.That's the reason why I use batteries during measurement. The switch mode charger is only used when not measuring.On the other side you could try to improve the EMF sensitivity by placing a 1-100nF capacitor at the output of the SVR reference.On your ADR441 devices you have 100nF at each output if I interpret the white board correct.I do not know wether the AD587 will be stable with capacitive loads larger than 1nF because 1nF is the maximum mentioned in the data sheet. Perhaps the best filtering will be a 100 Ohms between the SVR output and the 100nF capacitor going to the high impedant input of the 34401A.With best regardsAndreas

author: Joe Geller
author_rank: Contributor
timestamp: December 27, 2013, 10:42:48 pm
content: yes, where there are EMI / RFI issues, a 0.1 uF film capacitor can be soldered in the two output pads closest together near the Vref+, Vref- outputs solder terminals. In one case, a user with more severe RFI pickup problems found the output remained ppm stable with a .33 uF film capacitor.SVR boards should always be powered where possible by a linear supply. We use a hp E3610A, however just about any transformer isolated open frame (linear, not a switcher) ebay surplus buy is okay too (cover up those AC terminals and add an input fuse with an OEM linear open frame unit). Two 9V batteries are okay for short term testing, but we cal'd at 15 V, so you probably want a 15 regulator if you want to try to cal to absolute. The SVR board with the trim jumper in draws about 3 mA (~2.3 mA with the trim jumper out).Unfortunately a 100 ohm output series R is too high for DMM 10 meg ohm inputs (okay for the HiZ 1 or 10 Gig inputs). The problem is that for a DMM 10 MegOhm input, 10 V corresponds to a 1 uA input current, so (IR) 100 ohms and 1 uA would give a 100 uV drop in Vref.Unfortunately the AD587 output can also be moved by nearby Cell phone transmissions (e.g. a cell phone on a belt clip) apparently coupled in through the output leads to the AD587 output stage (now a well known problem). A metal box does not help for this problem. Here, the solution is to remove cell phones from the immediate area while using the SVR (just not in a pocket or on a belt clip next to where you are working, another room is usually fine).

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 29, 2013, 05:03:09 am
content: @Andreas: As I have mentioned in several posts before, I use a transformer wall wart and a linreg. The wart in the video is just there - unused.Strange you both are talking about decoupling caps now - that was what I tested the other day after I put up the video here. Result: I killed the AD587 by reversing polarity. Joe knows already - he has reserved one of the few left for me. Thanks.I have both AD586 and AD588. They show the same EMF/EMI effect. I think what Joe says about the output is the main factor. I have another video where the AD588 has long leads to the DMM. All I need to do is to cross the + lead from ref to DMM with another cable that is not even carrying current or has any voltage potential (it is not connected to anything). As a result I get 50 or 100 uV change in the reading. Many other refs are like this. But some, like the ADR441, is more or less immune to this effect.Anyway - I am OK with it. As long as one knows what is going on, one can beware of it and sometimes account for it. So one thing I have learned from this thread is which cabling can be critical.But - I am now free of my obsession with precision. I have managed to get two DMM modules for 34970A up and running, so now I have three 6 1/2 digit DMM's that all shows different measurements for the same source with the same cables. No more wondering if my first DMM - the 34401A - is correct anymore. They are all ca. 10 years away from calibration. I can get them checked and calibrated any day I want (if I want ...)So I will concentrate more on long term stability which imo is a much more fundamental and valuable aspect than knowing approximately how many microvolts I am away from 10.0 V today (the same number surely won't repeat itself tomorrow).

author: Andreas
author_rank: Super Contributor
timestamp: December 29, 2013, 08:23:13 am
content: Quote from: quantumvolt on December 29, 2013, 05:03:09 amA 100uV change cannot be explained by a transformer and a linear regualtor.So I would expect a switchmode supply connected to the system.Or a large EMC field coupling into the measurement area.Are the ADR441 really less imune if you remove the blocking capacitors from the output of the ADR441?Any semiconductor IC has (sometimes parasitic) ESD protection diodes at each pin.These diodes rectify any EMC on attached lines giving a offset voltage to the input/output voltage.So the influence should be nearly independant from the device used (under same conditions).With good decoupling the effect should be minimized to below a few uV.With best regardsAndreas

author: Joe Geller
author_rank: Contributor
timestamp: December 30, 2013, 04:57:06 pm
content: A SVR board can be used with a reasonable quality linear power supply. Linear power supplies include a built in isolated transformer. "Linear power supply" refers to more than just a linear regulator.I do not agree with the assertion that a DMM reading a SVR board is often or always in anyway rigged or set up. It is certainly the case that a setup can induce errors, often very large errors. However, that does not translate to therefore it can't work, or if anyone else gets better results, they must have rigged the test.To demonstrate, I tore down my working test setup and replaced it with one power supply, two set of standard Agilent leads, and one SVR board and moved a Web Cam towards and away from the board. I am not able to repeat the effect at the 1 ppm level that has been reported as applying to all reference measurements. There is no film capacitor (0.1 uf is ok) across the output terminal of this SVR board.http://youtu.be/uUh9j9XaLLcCertainly some shielding and RFI/EMI precautions can be helpful. When making precision measurements, we often use a ferrite on the high side leads. Also, we often leave a ferrite clamped over the power supply leads. However, as you can see in this video, there is nothing fundamental that indicates variations of several ppm (e.g. 50 uV) by approaching or touching the leads.Here, the value just happens to fall between 9.999 93 and 94, thus the last digit change from time to time. However, there are certainly no changes of tens of uV just out on the table with open unshielded leads. Almost forgot, this 34401A (10 plc integration time) reads 9.999 94 on the Fluke 732B. As others have pointed out many times, calibration can mean your DMM has been calibrated to and agrees within some level of precision to a calibration reference or standard, or calibration can mean you know to within some range of certainty what the current "as found" calibration of the DMM is.Possibly you were seeing capacitive coupling from your web cam back to a non isolated switching power supply via the SVR Board. A linear regulator following such a supply would not solve that problem. After thought: Note that one of the reasons it is possible to make a 10 uV resolution measurement with open leads is the DMM power line cycle integration time. 10 plc and 100 plc integration times create a very effective filter with deep attenuation at multiples of power line frequencies. Therefore some level of power line noise (e.g. power line signals and low multiples associated with linear power supplies) are very well attenuated. However, 10 plc and 100 plc integration times might be completely ineffective for some switcher related noise signals.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: December 31, 2013, 04:05:54 am
content: First of all - the AD586/87/88 are imo good refs. And the Geller SVR board which is an AD587 with support circuitry on a PCB - 'burned in', tested and calibrated - is imo a good product. Thanks to the SVR board I can be reasonably sure that my (10 years since calibration) DMM is within spec on the 10 V DC range.Furthermore - I do not doubt in any way the knowledge and experience of Joe and Andreas. On the contrary - Joe's papers/links on his website and Andreas' posts here and on volt-nut have provided me with a lot of information not easily found in datasheets and application notes.I just report what is possible with a 'bad' setup. If it is possible for me to create these effects by 'rigging' the setup (4 leads - i.e. the "topology" of +/- DC supply and +/- Vref out to DMM), then it also possible to do it by mistake. And everybody knows that sometimes the voltages changes when we move our body or turn on/off the bench light. [The AD588 that shows similar effect as the AD587 has 10 nF decoupling on the output.]As a consequence I will make a permanent rig (in a "fish tank" transparent "wind-proof slightly ovenized" case) with a commercial multi-channel 6.5 digit DMM (16 differential inputs with 16 short fixed-position twisted +/- lead-pairs from 16 refs to DMM) and a commercial lab power supply (Agilent 34970A / 34902A / HP E3630A). That way I can measure many refs with documented equipment without touching anything. A fixed but flexible thing like in the first picture below.Anyway - whether people believe it or not - I use "pure, barebone" isolated transformer, bridge rectifier and electrolytic capacitor to linear regulator supplies for all analog and mixed signal devices. My switch mode fleabay wall warts are all for my several Arduinos and other gadgets that I use in digital mode only.I won't dwell more on this. I'll finish this thread with some kind of conclusion about the long time stability for the eight ADR441 chips.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 29, 2014, 07:03:30 pm
content: Any news on this?

author: quantumvolt
author_rank: Frequent Contributor
timestamp: March 29, 2014, 09:49:44 pm
content: Quote from: CaptnYellowShirt on March 29, 2014, 07:03:30 pmNo - at least not now. They are still running. I got tired of discussions of my somewhat sloppy method, so I have cleaned up the PSU common connections and started over. Also I run them from a HP 3630A (no credibility issues as to be a transformer based linear series regulator).If one reads the thread, it should be clear that imo the refs are unproblematic quality precision voltage for a few bucks.When and if I post again, it will be when the refs have their 1st powered birthday.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 30, 2014, 12:41:52 am
content: Quote from: quantumvolt on March 29, 2014, 09:49:44 pmYeah I glossed over a lot of that crap. I think you said it best in your first post: "There is quite a lot of (different ?) 'knowledge' and experience distributed on this forum. I for one am in for learning ..."There's really only one way to know something and that's to try. Everything else is just feather preening.For one, I'll be interested in hearing how it went.

author: macfly
author_rank: Contributor
timestamp: March 30, 2014, 01:35:12 pm
content: Mhm,On the other side you could try to improve the EMF sensitivity by placing a 1-100nF capacitor at the output of the SVR reference.On your ADR441 devices you have 100nF at each output if I interpret the white board correct.I do not know wether the AD587 will be stable with capacitive loads larger than 1nF because 1nF is the maximum mentioned in the data sheet. Perhaps the best filtering will be a 100 Ohms between the SVR output and the 100nF capacitor going to the high impedant input of the 34401A.With best regardsAndreasI agree with Andreas. But cap's are not the only way. EMF sensitivity drives me sometimes near crazy. For my Geller Reference, I made a serious solution, to get rid of all these unwanted RF:Metal housing, battery operated, no connection wires to the DMM:

author: Andreas
author_rank: Super Contributor
timestamp: March 30, 2014, 01:43:39 pm
content: Quote from: macfly on March 30, 2014, 01:35:12 pmHello,there are still (short) connections to the DMM.Try to put the DMM into the metal housing.Otherwise you will have to filter the both outputs against the housing. (Common mode)And the + against the - (Differential mode).With best regardsAndreas

author: macfly
author_rank: Contributor
timestamp: March 31, 2014, 10:09:13 am
content: Quote from: Andreas on March 30, 2014, 01:43:39 pmHi Andreas,I agree with you. But unfortunately my DMM, a HP 3457A, has no 'guard' connector, ase.g. the 3456A has.Regards,macfly

author: bingo600
author_rank: Super Contributor
timestamp: April 02, 2014, 02:39:07 pm
content: Quote from: macfly on March 31, 2014, 10:09:13 amHmm strangeHP specificaly mentions it in this publication (Page. 15 ff.)http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1986-02.pdfActually a nice walkthrough of the 3457A/Bingo

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 02, 2014, 02:56:24 pm
content: Quote from: bingo600 on April 02, 2014, 02:39:07 pmThe 3457a has an internal guard shield (e.g. not mains-earth grounded), but no way to hook into that from the outside like many other high-resolution dmm's offer.

author: macfly
author_rank: Contributor
timestamp: April 02, 2014, 05:08:08 pm
content: Hmm strangeHP specificaly mentions it in this publication (Page. 15 ff.)http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1986-02.pdfActually a nice walkthrough of the 3457A/BingoThanks for the link - indeed, a very interesting article!Regardsmacfly

author: JoeN
author_rank: Frequent Contributor
timestamp: April 02, 2014, 05:58:39 pm
content: I can't believe no one asked this.How did you get a sample of 10 ICs?Analog will only ever send me two. Thought that does work for me.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: April 02, 2014, 09:49:50 pm
content: As I wrote in Reply #4 in this very thread:"When I asked for these devices I think I said 'a handful different references from the ADR44x family'. I was planning to compare them to my LTC6655 2.5V and 5V references."Obviously - as is very, very common these days - someone didn't read what I was asking for, and sent me 10 equal devices.Concerning begging method: I just sent a polite and well formulated email to ADI ("Contact us" on the web site). With no promises on what I would do with them, and stating clearly that I would only accept them if ADI demanded nothing in return.If one learns to read, think and write - and has some (even just a private) cause - I guess one can sample a 3458A ...

author: JoeN
author_rank: Frequent Contributor
timestamp: April 03, 2014, 05:04:43 am
content: Quote from: quantumvolt on April 02, 2014, 09:49:50 pmIn my case, they allow you to register and then allow you to order online without resorting to emails. I've been quite successful this way, it's just you can't order more than 2 devices per part number and 4 different part numbers per order. You can place two orders per month. On the other hand, you can order two of the $70 devices too and they have never denied me. Way back in the day I begged U.S. Robotics for an 14.4K HST modem on a BBS system operator discount though I wasn't running a BBS at that moment (I had for years). I just told them I was intending to set a new one up. That had to be done via old fashioned letter. I ended getting one of their $600 modems for something like $250. The prices back then were really insane.I guess someone made a judgment call since you were ordering a super cheap part, why not give you a bunch of them? My last order had a AD5791 DAC, a $60 part. I doubt I could sweet-talk them into sending me 10 unless I had an Agilent or Tektronix email address. OTOH, 2 are enough for my purposes anyway. They sent it no problem.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: April 03, 2014, 05:28:34 am
content: Well - I am sorry I misunderstood you. I do not register and try to sample as much dollar worth as often as I can. I guess the real cheapos double-sample by also making an account in their little sister's name ...I got a few refs that I do not need (I have more precision refs than I will be able to power up before I die) for an experiment. The experiment is closed for now.This thread was about 'burn-in' / drift in voltage references. Please post your sampling advice somewhere else. Thank you.

author: JoeN
author_rank: Frequent Contributor
timestamp: April 03, 2014, 05:46:40 am
content: Quote from: quantumvolt on April 03, 2014, 05:28:34 amIt is not my intention here to criticize your sample acquisition method. It's just that your way of doing it was unknown to me and I appreciate that you explained it. In return, I explained how I do it in case you were not familiar with it. In any case, I didn't order that part just to maximize the published price of the chips I am getting. I took it specifically because AD has a very nice circuit note on how to construct a 1PPM voltage source from this part:http://www.analog.com/en/circuits-from-the-lab/cn0191/vc.htmlAnd I am building it. It's almost done. It is being built around an ATTMega328P controller and an Analog voltage reference (interestingly, they suggest a Linear voltage reference).On that order I also ordered the AD8675, AD8676, ADR445. These are all far less expensive parts (buffer amps and a precision voltage source) needed to construct the circuit.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 03, 2014, 06:01:01 am
content: Quote from: JoeN on April 03, 2014, 05:04:43 amIts sad to think some people today don't even know what a modem handshake sounds like.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: April 03, 2014, 07:33:43 am
content: Quote from: JoeN on April 03, 2014, 05:46:40 amVery good. Many people here are interested in AD5791 and the LT ref that has an unnamed footprint on the ADI demo board - namely LTZ1000.I suggest you show your project either in the LTZ1000 thread, the Seven Decade Voltage Calibrator thread, or make a new one.I would be very interested in your project. Good luck.

author: Andreas
author_rank: Super Contributor
timestamp: April 03, 2014, 07:29:36 pm
content: Quote from: JoeN on April 03, 2014, 05:46:40 amWhich Linear reference?I would use a 10V reference (AD587 in CERDIP for long term stability) for this circuit together with a temperature sensor for correction.Otherwise the most expensive parts will be the resistors to scale the 5V to +/- 10V.With best regardsAndreas

author: quantumvolt
author_rank: Frequent Contributor
timestamp: April 03, 2014, 07:47:39 pm
content: EVAL-AD5791SDZ_LTZ1000A.pdf (145.8 K)EVAL-AD5791SDZ Bill_Of_Materials.xls (40.5 K)AD5781_91_Gerbers.zip (447.6 K)Location:http://ez.analog.com/message/67799#67799

author: JoeN
author_rank: Frequent Contributor
timestamp: April 03, 2014, 11:09:27 pm
content: Quote from: Andreas on April 03, 2014, 07:29:36 pmThanks for the input. The part that AD suggests is LTZ1000 like quantumvolt wrote. On the eval board that you can *buy* from Analog, there is an unpopulated space for this part, or you can provide your own reference. I've included some circuit diagrams and the image of the board they sell.I chose an ADR445 as the reference. Was this a bad move? My main motivation was that it was free but still seems to have very good specs. Also, I don't have the precision resistor values needed to precisely double the voltage but I do have matched pairs of .01% Vishay resistors (odd value - 681 ohm) that are allowing me to create a precise -5.000V off the 5.000V source. So I am giving up on -10V/10V and going with -5V/5V, at least the first go-around. I know this is all fishy and is extremely unlikely to get me to the promised land of 1PPM but hopefully that reference is at least stable so I can trim it out in software.First image, the unpopulated reference on the eval board. Second image, the eval board I am trying to somewhat clone. Third image, general suggested application schematic for the DAC.

author: Andreas
author_rank: Super Contributor
timestamp: April 04, 2014, 05:35:10 am
content: Quote from: JoeN on April 03, 2014, 11:09:27 pmHello,now its clear why they recommend a LT device. The LTZ1000 is the best of all references.I have only tested the ADR4550B which is specced 25ppm/khr against 50ppm/kHr ageing drift of the ADR445.The drift of the ADR4550B (ADC18) was about 90ppm for the first half year. And even after this there are some "jumps" (due to humidity changes?) of a few ppm each week that I do not have on a well aged hermetically tight device like the AD586LQ (ADC13).With best regardsAndreas

author: JoeN
author_rank: Frequent Contributor
timestamp: April 04, 2014, 07:59:06 pm
content: Quote from: Andreas on April 04, 2014, 05:35:10 amI just checked and Linear won't sample this part.

author: Andreas
author_rank: Super Contributor
timestamp: April 04, 2014, 09:25:23 pm
content: Quote from: JoeN on April 04, 2014, 07:59:06 pmThey know that you cannot afford the 5 precision resistors at $30 each ;-)The 2nd best is the LM399 (at stock @ digikey)With best regardsAndreas

author: JoeN
author_rank: Frequent Contributor
timestamp: April 05, 2014, 12:30:12 am
content: Quote from: Andreas on April 04, 2014, 09:25:23 pmOTOH that part can be sampled.

author: Andreas
author_rank: Super Contributor
timestamp: April 05, 2014, 06:01:58 pm
content: Hello,even a clean PCB absorbs some humidity and swells.The same is with plastic DIP packages.At least so much that you can see it in the ppm-range.My LT1027CCN8-5 have a humidity sensitivity of 0.5ppm/% rH.The only way to avoid this is to use hermetically packages (metal or ceramics) and seal the pins with glas.But even in this case you have to carefully decouple the package from the PCB.Otherwise the humidity change of the PCB will create similar changes in the range of about 0.5ppm/% rH.With best regardsAndreas