DC Voltage References Battle - Overview of market - Page 1
Forum section: electronics / projects

author: TiN
author_rank: Super Contributor
timestamp: October 01, 2015, 04:39:29 am
content: Hi all,Friend of mine asked me recently to check his DC voltage reference, cheap AD584KH-based module, and provide calibration if needed. I went on EEVBlog to check, if anyone already tested or reviewed reference he had, found bunch of threads, but not a single source with all data in one place. This brought me an idea, what if we summary all available boards from different people, and make overall spreadsheet with their specs/cost/performance level?Yes, it sounds like "we have 14 standards, let's make one common standard. Now we have 15 standards", so feel free to blame me on it.We have bunch of threads about LTZ1000, LM399-based designs, but I think they are time-consuming and overkill for someone who just want pick a ref to calibrate their gear, within given budget.SummaryPhotoModule nameTypeBased solutionOutput voltageAccuracyTempcoCostNotesAD584KH TaobaoZener IC, non-ovenizedAnalog Devices AD584KH2.5, 5.0, 7.5, 10.0 VDC+/-500ppm?+/-30ppm15$External power, low costHP 3458A A9 board (STD)Super-zener, ovenizedLinear LTZ1000A7.2 direct VDC2%+/-8ppm$100-700Available from KeysightHP 3458A A9 board (002)Super-zener, ovenizedLinear LTZ1000A7.2 direct VDC2%+/-4ppm$984Available from KeysightN/AHP 3458A A9 board (HFL)Super-zener, ovenizedLinear LTZ1000A7.2 direct VDC2%+/-2ppm$2195Orderable from KeysightReviewsAD584KH quad-voltage reference -TiN's review- in works

author: Vgkid
author_rank: Super Contributor
timestamp: October 01, 2015, 04:52:02 am
content: I look forward to more additions, subscribed.

author: BravoV
author_rank: Super Contributor
timestamp: October 01, 2015, 05:11:04 am
content: Thanks, subbed.Side note, wonder why the MAX6350 is not oftenly discussed here in this forum. From the spec sheet, with TC of 1 ppm/C , initial accuracy 0.02% and 30ppm/1000hr longterm stability, not too shabby right ?

author: Mr.B
author_rank: Unknown
timestamp: October 01, 2015, 05:17:04 am
content: Bookmark.Thanks for your effort TiN.

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 01, 2015, 06:04:01 am
content: This is going to be helpful, also subbed

author: ez24
author_rank: Super Contributor
timestamp: October 01, 2015, 06:48:49 am
content: Quote from: crispy_tofu on October 01, 2015, 06:04:01 amCrispy - are you going to offer Dave some stinky tofu when he delivers the meter? I miss it.To OP - do you mean components or completed circuit boards that people sell? No mention of price range if this matters.

author: TSL
author_rank: Regular Contributor
timestamp: October 01, 2015, 07:15:50 am
content: These little standards are handy...http://www.voltagestandard.com/I have one of their DMM check units that I'm very happy with.

author: ez24
author_rank: Super Contributor
timestamp: October 01, 2015, 07:54:32 am
content: Quote from: TSL on October 01, 2015, 07:15:50 amme too

author: eas
author_rank: Frequent Contributor
timestamp: October 01, 2015, 08:03:58 am
content: I have collected too many of these.I have the plexi cased AD584KH reference from the same maker as the bare board you reviewed, TiN. I also have yet another bare PCB AD584LH reference, an AD588BQ board, an uncalibrated/untrimmed Geller, and a DMMCheck+What I don't have is a traceably calibrated meter or a calibrated reference beyond the DMMCheck+ which only gives 5 digits.

author: BravoV
author_rank: Super Contributor
timestamp: October 01, 2015, 08:38:35 am
content: Complementing this thread, there is an excel file converted into PDF by Dave that contains all known voltage reference chips (heated and unheated) that is compiled by JBeale ->Voltage Reference Chips (2013)

author: crispy_tofu
author_rank: Super Contributor
timestamp: October 02, 2015, 07:01:00 am
content: Quote from: ez24 on October 01, 2015, 06:48:49 amLol, I wish... the meter was delivered (thanks Dave!) but I was away at the time and my parents said no anyway

author: HighVoltage
author_rank: Super Contributor
timestamp: October 02, 2015, 07:34:42 am
content: Great idea.I have a few to contribute.

author: ez24
author_rank: Super Contributor
timestamp: October 02, 2015, 07:40:18 am
content: Quote from: HighVoltage on October 02, 2015, 07:34:42 am? A few of what?- tofu- meters- chips (IC or potato ?)- something elseRight now I would like some stinky tofu

author: tszaboo
author_rank: Super Contributor
timestamp: October 02, 2015, 10:25:03 am
content: And then, there is this.

author: ralphd
author_rank: Frequent Contributor
timestamp: October 02, 2015, 12:14:46 pm
content: Quote from: BravoV on October 01, 2015, 05:11:04 amOr the 6126 with 20ppm/1000hr?After some searching around on Aliexpress I found I can get them for $3. So less than double the cost of a REF5050. No tout like the ref5050 though, but I'm still thinking of ordering a couple.

author: nctnico
author_rank: Super Contributor
timestamp: October 02, 2015, 12:50:01 pm
content: You can also buy PLC calibrators on Ebay. These have an adjustable voltage and current. The more expensive ones claim an accuracy of 0.01% (100ppm).

author: Andreas
author_rank: Super Contributor
timestamp: October 02, 2015, 07:38:52 pm
content: Quote from: ralphd on October 02, 2015, 12:14:46 pmHello,according to my own measurements the (typical) datasheet values have nothing to do with the real world.The ageing numbers are only valid (if at all) for the first 1000 hours after production or first soldering.(some datasheets specify the second 1000 hours to keep the number comparable to the usual 20-30 ppm/kHr).A really good (buried zener) reference will settle after around 6-12 month to a ageing rate below 10ppm/year.e.g. around 2 ppm/year at room temperature.The MAX6350 has a low T.C. but my 2 samples have a constant ageing rate of 10ppm/year. (over 3 years).Whereas other buried zeners (AD586LQ) go down to the 2 ppm/year after initial drift.https://www.eevblog.com/forum/projects/newbie-precision-reference-calibrated-with-the-3478a-dinosaur/msg538036/#msg538036The MAX6126 (and REF5050) is a bandgap reference. So even when specced with 20ppm/kHr it will beoutperformed by a buried zener reference.The housing of the reference plays a large role in stability.Metal can or ceramic hermetically packages give much more stability than a DIP8 housing.A dip 8 housing gives up to factor 3 more stability against a SO-8. (found in a MAXIM datasheet).The long term stability of the MSOP package is specced factor 5 worse than SO-8 for the MAX6126.So size matters.So my personal ranking for references ishermetically sealed:1. LTZ1000/LTZ1000A2. LM3993. AD587UQ/AD586LQ(3.5 LT1027CCH/BCH: unobtanium)4. LT1236AILS8plastic:5. AD586MNZ6. LT1027CCN8 (low ageing but large humidity drift)7. MAX6350CPA/MAX6250ACPA (low humidity but large ageing drift)And after that all the other references.with best regardsAndreas

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 02, 2015, 08:39:11 pm
content: Quote from: Andreas on October 02, 2015, 07:38:52 pmHi Andreas,Do you have any experience/opinion on the ADR01/02BRZ and ADR3450ARJZ?CheersAlex

author: pelule
author_rank: Frequent Contributor
timestamp: October 02, 2015, 09:17:35 pm
content: QuoteHi Andreas,Do you have any experience/opinion on the AD588BQ/AD588AQ?http://www.analog.com/media/en/technical-documentation/data-sheets/AD588.pdfBRPeLuLe

author: PA4TIM
author_rank: Super Contributor
timestamp: October 02, 2015, 10:05:17 pm
content: I build standards using a LM399, one with a LT1027B and 3 versions with 4x431 parallel. Those performed well. Also used a LT1021 -10. I builded those standards only because I wanted to build some to learn more about Vrefs. I have no real need for it because I have more standards like a Guildline standard cell cabinet with full history, a Fluke 731, 750, 760, 720, 332, 510, an ESI decavider and a Philips PM2480 standard. Besides those some Tektronix scope calibration stuff, time standards and passive standards (LCR)I miss a temperature standard (but I repaired several from my customers so I can check my gear against those )How do you know the Vrefs are still correct. My LM399 drifted over 100 uV the first six months, powered 24/7 connected permanent to a 7,5 digit meter the first months. Short time drift was influenced most by relative humidity in my lab.

author: Andreas
author_rank: Super Contributor
timestamp: October 02, 2015, 10:11:24 pm
content: Quote from: Alex Nikitin on October 02, 2015, 08:39:11 pmHello,the only test in this range (XFET) was (only 1 new sample) ADR4550 (violett = ADC18)against two (aged) LT1027 in plastic DIP (ADC4 + ADC8)and one (aged) AD586LQ (ADC13) in CERDIPAll measuring a LTZ1000A with a precision 2:1 divider (LTC1043).I think it gets clear why I did not try a 2nd sample.nearly 100 ppm drift over 300 days and not calming down to a sub 10ppm level.Quote from: pelule on October 02, 2015, 09:17:35 pmno experience.Opinion: should behave similar to AD586LQ/AD587UQWith best regardsAndreas

author: eas
author_rank: Frequent Contributor
timestamp: October 03, 2015, 04:15:53 am
content: Quote from: Andreas on October 02, 2015, 10:11:24 pmI have a cheap Chinese board with an AD588BQ as well as some cheap bare chips that are either NOS, or pulls from sockets in old equipment. I have a week or two of data on the board, but haven't done anything with it. Not super useful either, given that I didn't have a temperature record for the period. I have an AD +-15V PSU module that I plan to use to do a long term test the bare ICs.One intriguing thing about the AD588 is that it has a couple of uncommitted low-dift, low-offset buffer amplifiers that can be used for kelvin sense of the output, making a precision current source (10mA, max), or...

author: pelule
author_rank: Frequent Contributor
timestamp: October 03, 2015, 08:47:59 am
content: QuoteI assume it is one of these offers from China, I have looked to also:http://www.ebay.de/itm/252001708799?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIThttp://www.ebay.de/itm/251943908859?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITI have daubt, this are really BQ version, as just the chip cost > 22 USD in higher volumes. Just assume this are "refreshed" JQ or AQ types.

author: pelule
author_rank: Frequent Contributor
timestamp: October 03, 2015, 09:03:25 am
content: Code:http://www.ebay.de/itm/252001708799?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIThttp://www.ebay.de/itm/251943908859?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITI have daubt, this are really BQ version, as just the chip cost > 22 USD in higher volumes. Just assume this are "refreshed" JQ or AQ types.EDIT: forgot to tell, it is offered for US $14,92 including shipment.I despite my daubts I have ordered, I have the original BQ and this offer is cheaper, than routing/ordering your own PCB. I don't care regarding the mounted chips. If this are real BQs great.I plan to mount that board into a temp. controlled chamber 35°C (+/- 0.01°K) and to do long term drift measures. Plan to post that results than.

author: Gyro
author_rank: Super Contributor
timestamp: October 03, 2015, 09:45:48 am
content: I have an AD588BQ that I've only played with fairly briefly so far. Having the on-chip opamps for Kelvin sensing etc is very useful. The only downside is that it all adds to the device dissipation (needing +/- 15V supply) and is compounded by any loading. The increased temperature rise exaggerates it's TC, although of course the temperature will stabilize at some point if the load is constant.Blessed are those lucky enough to have bought one of Joe Geller's AD587LQ based SVR-T while he was still producing them.EDIT: Just had an idea - I wonder if one of the opamps could used to implement a simple on-die oven

author: plesa
author_rank: Frequent Contributor
timestamp: October 03, 2015, 10:21:58 am
content: This table can be useful ( I do not remember who is author of this, but it was posted on eevblog some time ago).https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=40252For me is favourite reference LM399AH, LTZ1000 (A) and LT1027.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 03, 2015, 12:09:32 pm
content: The extra OPs inside the AD588 are not usefull for temperature controll, as there is no temperature sensor on the chip.The more valuable part are the on chip resistors to get specific values for the ref voltage. Even than one might decide to use external OPs to reduce power consumption.There are a few ref chips like Ref02 that do have a temperature sensor on chip and could in principle be used to get them termalized. Up to the point of using a LM723 to controll its own temperature.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 03, 2015, 01:28:40 pm
content: Quote from: Andreas on October 02, 2015, 10:11:24 pmThank you, Andreas, however the ADR01 is a refined band-gap, pin compatible with the REF01. The "BRZ" version in SOIC8 suppose to have better than 3ppm/C (1ppm/C typ) tempco and less than 50ppm/1kh long-term drift. I'm looking at that particular reference as it has a temperature monitor output and can be compensated to almost zero tempco in a narrow range, I think.The ADR3450ARJZ on the other hand is possibly the cheapest option for less than 10ppm/C tempco.CheersAlex

author: eas
author_rank: Frequent Contributor
timestamp: October 03, 2015, 03:47:36 pm
content: Quote from: pelule on October 03, 2015, 08:47:59 amYes, it is one of those. Same board design, but my PCB is green. The 15v batteries it is intended to take are hard/expensive to get in the US.It could be a relabeled version of one of the JQ or AQ chips, but I doubt it since the labeling is embossed into the ceramic. I suppose someone could have gone to the trouble, but that seems unlikely. The bare chips I purchased on the other hand...My "lab" has been packed up while my inlaws visited, but they are leaving today. I'll unpack it and collect some voltage + ambient temp readings over a few days.

author: Gyro
author_rank: Super Contributor
timestamp: October 03, 2015, 05:32:19 pm
content: QuoteSorry, I should have been clearer, what I was thinking was more in terms of having a temperature sensor (diode or thermistor) strapped to the ceramic body and using one of the opamps as a combined comparator an heater. The whole thing being well insulated of course.Another Edit: I suppose the opamp could be used to drive an external heater transistor strapped to the other side of the package too. Maybe the whole idea is a non starter as it would also need scaling resistors to compare the temperature sensor to the main reference (with their own TC and drift).

author: Andreas
author_rank: Super Contributor
timestamp: October 03, 2015, 05:49:05 pm
content: Quote from: Alex Nikitin on October 03, 2015, 01:28:40 pmHello,sorry for mixing up. I only know ADR as XFET (ADR445, ADR435, ADR425, ADR4550 ...)But Band-Gap references also suffer from larger ageing than buried zeners.(at least for the reference element itself).If you want to compensate the T.C. to get further improvement then 2 other effects will annoy you:1. humidity: may be up to 0.5ppm/% relative humidity for plastic packages(you can see this in the curve for the LT1027CCN8-5 of ADC4 + ADC8)2. Thermal hysteresis. This depends on IC package but may bein the 10-30ppm range especially for non stiff (small) packagesfor a small temperature range (e.g. 10-40 deg C).Thermal hysteresis is also dependent on temperature change speed (gradient).I have already thought of using the trimming pin of a LT1236AILS8-5 as temperature output to compensate its T.C.But this needs buffering and probably a 2nd high resolution ADC to get a temperature resolution high enough toget good results without additional temperature steps in the output.Another possibility for temperature compensation is described on the page of geller labs.http://www.gellerlabs.com/Voltage_References/SVRTH/SVR%20THR%20Sch.jpgThis can be used with every reference with a trim pin for a small temperature range.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: October 03, 2015, 06:11:35 pm
content: Quote from: TiN on October 01, 2015, 04:39:29 amHello TiN,it would be good if you check the voltages of the AD584 after 1 year again in your review.From a german forum I have the figure of 1.76 mV Drift for the 10V within 1 year against a PM2534 Multimeter.So for me the AD584 references are perhaps a cheap way to import the "volt" in you home lab.But you should not rely on that the voltages are stable over a longer time.with best regardsAndreas

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 03, 2015, 06:14:23 pm
content: Quote from: Andreas on October 03, 2015, 05:49:05 pmHi Andreas,It is quite easy to make independent adjustments for both voltage trim and tempco, to compensate the slope at a particular temperature. You don't need a DA-AD conversion for that.Also, I have an old idea (possibly 20 years old) about a voltage reference, however up until now I've never tried it in practice (silly, I know). It is a very simple circuit and easily allows me to adjust it to less than 10ppm/C tempco at room temperature. With all this talk about stable references I've wired it up today and will see how stable it is till tomorrow (my lab gets about 5C cooler overnight). It is just a good fun to make a reference out of standard parts, not designed to be a reference! Right now it is on the bench, in open air, and the voltage stays inside a +/-2ppm range for an hour so far.CheersAlex

author: TiN
author_rank: Super Contributor
timestamp: October 03, 2015, 06:16:12 pm
content: Woa, lots of activity here, need to catch upAndreasI'm not sure that would be possible, as I'll send it to my friend in Ukraine, and shipping it back and forth would cost ten times more than actual reference.And it's not supposed to be voltage standard by any mean, only like a transfer standard.

author: pelule
author_rank: Frequent Contributor
timestamp: October 04, 2015, 10:41:10 am
content: QuoteFor a temp-control you need a "heater" and a "sensor".The "sensor" should have an as close as possible thermal connection to the chip.The "heater" isn't that critical, but a close thermal connection would support a good regulation and a minimum thermal mass.At the u723 the power transistor was the "heater", the -2mV/°K base-emitter voltage drift of the current control tranisitor was "semsor".At the AD588 it might be possible to use the offset drift (~1µV/°K) of one of the OpAmps (A3, A4) as a "sensor" by amplifying it with for example a gain of 100.000 (~100mV/°K) and use an opamp as the "heater" by driving a load (up to 10 mA @ 15V = ~150mW).

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 04, 2015, 11:09:34 am
content: Quote from: Alex Nikitin on October 03, 2015, 06:14:23 pmI've opened aseparate thread on that reference.CheersAlex

author: plesa
author_rank: Frequent Contributor
timestamp: October 04, 2015, 07:50:18 pm
content: Quote from: Andreas on October 03, 2015, 06:11:35 pmI can check on two AD584JH in my drawer ( worse spec than KH ) If you want.

author: Andreas
author_rank: Super Contributor
timestamp: October 05, 2015, 06:52:48 pm
content: Quote from: plesa on October 04, 2015, 07:50:18 pmHello plesa,on the one side it would be interesting (hermetical package) if all AD584 are that bad (> 1.7 mV in 1 year) or if it was an outlier.on the other side: the devices have much too much T.C. and I measured >10 ppm hysteresis over a 10-40 deg C range.Since I am looking for 5V references with- humidity stable behaviour (hermetical package)- T.C. around 25 deg C with less than 1 ppm/K- hysteresis of less than 1 ppm over a 10-40 deg C band.I decided to put my single sample of AD584JH back in the drawer.And since the AD584KH is obsolete by the manufacturer since years the probability ofrebranding/remarking of all those KH devices is very high.I also made the experience that the higer graded devices are not always better at room temperature.Usually the adjustment of T.C. is made at the temperature limits.The temperature gradient near 25 degrees may suffer from this procedure.With best regardsAndreas

author: lars
author_rank: Regular Contributor
timestamp: October 19, 2015, 06:20:08 pm
content: In beginning of June I bought one AD584KH board with measurement data like the one TiN tested. It arrived after two weeks and the label said 10.00262V at 21C measured with an Agilent 34401 in 2014 (I have not cared about the 2.5, 5 or 7.5V yet). I had it powered a couple of days. As it was summer and I have no AC in my lab the temperature went between 23 and 27C. The temperature coefficient was -3ppm/C so extrapolated my reading at 21C was 10.00266V (with 5ppm uncertainty) that is +4ppm from original reading. Now I have run it for a couple of days again. Now with about 19-23C. At 21C the reading is 10.00268 that is +6ppm from original reading, not bad for this low price. The AD584KH fluctuates a couple of ppm over the days (and years for another old AD584LH I have!).I was really glad to see that the AD584KH board seems to have low sensitivity to air around. My first experience with an AD581KH (very similar to the AD584KH except it is only +10V) more than 20 years ago was that I had to cover it from air movements. That time I had it with long leads on a breadboard and very soon mounted it in a box. Probably the mounting of the AD584KH with almost no leads to the board is very clever in this case.Are the AD584KH really obsolete? I see that you can buy it at the Analog Devices web site and Mouser also have stock.Lars

author: Andreas
author_rank: Super Contributor
timestamp: October 19, 2015, 07:38:36 pm
content: Quote from: lars on October 19, 2015, 06:20:08 pmHello Lars,sorry I mixed that up with the "L" grade which was removed between Revision B and C of the data sheet.There are still many boards with LH types on the web:http://www.ebay.com/itm/AD584LH-4Ch-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-15-/261320055120?hash=item3cd7e39950:g:-00AAOxy2YtRvgw9With best regardsAndreas

author: lars
author_rank: Regular Contributor
timestamp: November 19, 2015, 06:11:27 pm
content: Now I have bought another reference like the TiN one. I also bought two other with the square battery on from two different sellers.Received the “TiN” style just after one week on Oct 20. This time the label said Agilent 3458A 2015 26C and the 10V was specified as 10.00801. I measured 10.000795. Have measured it again today at 10.00797 so just about 5ppm below. The temperature coefficient was about -3pppm/C again but the datecode on the AD584KH said 9213 (last time 0635). So both of my 584KH board has been within 10ppm not bad. My guess for an uncertainty specification would still not be better than 50ppm (K=2). My assumptions are 30ppm from the Agilents, 30ppm due to temperature coefficients up to 15ppm/C and the customer is able to be within 2°C from stated temperature, and finally maybe 20ppm from drifts since measurement. This summed, as in GUM, gives about 50ppm. My thought is also that sellers should be conservative as these products goes to hopefully young hobbyist that can´t afford to buy a lot of references to build up statistical confidence. Also giving correct measurement uncertainties could help young (and old) to learn the importance of measurement uncertainties I hope.I have also received one of the other two of the different style but no measured values were supplied. It had an AD584LH with datecode 1015. I measured 10.00231 at 23C both at arrival and now. The temperature coefficient is about +3ppm/C.I enclose a chart from Excel that might be interesting for some. It shows a few selected references of my (about) bimonthly checks. As reference I use an AD581KH with datecode from 1984 that is only powered a couple of hours every second month. It is actually 10.00367 and has a temperature coefficient of about +1.5ppm/C and no temperature compensation but as most of my DIY references contains a 10k NTC (same as Digikey BC2301-ND). As a side note the drift of the NTC is below my measurement uncertainty for temperature and that over more than 20 years!The AD584 is an AD584LH with date code 7945 and made in Mexico stamped on. It has a temperature coefficient of about +1.5ppm/C. It is only powered up every second month.The three AD584-2 to -4 are AD584JH with datecodes from 1989 and have temperature coefficients from 0 to -6ppm/C. They were only powered up sporadically 1998-2001 but since 2001 they have been mounted together with some other references in a box and continuously powered and the internal temperature was about 36°C inside in average (ouside 23C). 2011 I completely rebuilt that box and took away the AD584´s.The AD688AQ is a ceramic package mounted with trimmers I salvaged and cut out from an DAC board more than twenty years ago. It is only powered every second month.Last the four REF102CM have datecodes from 1998 I think. Around 2000 I mounted two each in a box with NTC temperature compensation. The REF102CM´s have been continuously powered since around 2000-2001. As can be seen they drifted the first years but probably not so much now.Lars

author: Andreas
author_rank: Super Contributor
timestamp: November 19, 2015, 06:29:27 pm
content: Quote from: lars on November 19, 2015, 06:11:27 pmHmm,why are there only 6.5 digits when measured by a 8.5 digit device?With best regardsAndreas

author: lars
author_rank: Regular Contributor
timestamp: November 19, 2015, 06:33:14 pm
content: I should also select a resolution of 10uV as the AD584 bandgap device is specified for 30uV p-p 0.1-10Hz if I remember correctLars

author: Andreas
author_rank: Super Contributor
timestamp: November 19, 2015, 06:45:07 pm
content: Hello Lars,with 100 NPLC (2 sec) integration time which I would choose for "precision" measurementsyou will have only a part of the 0.1-10 Hz noise.With best regardsAndreas

author: lars
author_rank: Regular Contributor
timestamp: November 19, 2015, 06:48:55 pm
content: You are correct but also remember you are in the flicker region. So just over minutes you can have at least a 1ppm shiftLars

author: splin
author_rank: Frequent Contributor
timestamp: November 26, 2015, 05:43:51 pm
content: Quote from: lars on November 19, 2015, 06:11:27 pmLars,Can you tell us anything about how you measure the NTC drift and how you calibrate it? What is your measurement uncertainty for temperature?Thanks,Tony H

author: lars
author_rank: Regular Contributor
timestamp: December 21, 2015, 02:54:43 pm
content: I have been fortunate to have access to calibrated temperature probes and calibrated my reference probes to them so I have about 0.2C uncertainty as best. As I have done measurements on my voltage and resistance references about every second month for around 20 years I have quite good statistics. If I do a regression analysis on the NTC´s compared to the outside probes I get about +-0.02C/year. The NTC´s are 10k Philips/BC Components same as the the Digikey BC2301-ND.Lars

author: klimm
author_rank: Contributor
timestamp: April 30, 2025, 09:52:40 am
content: I am looking herehttps://xdevs.com/review/dcvref_table/at the Accuracy/ppm column and I am confused by the fact that AD588 is expressed in mV (not ppm like others)Question; I suppose I should translate to ppm(for comparison reasons) with respect to the output voltage, in this case 10V, so accuracy expressed in ppm should be10V/0.001V= 10,000Am I computing wrong here?The DS's gives 587's initial error 5mv and 588BQ's error is 1mv so I don't get why 587 in this table table has accuracy of 10ppm

author: Kleinstein
author_rank: Super Contributor
timestamp: April 30, 2025, 10:39:18 am
content: The AD588 seems to give both 5 V and 10 V. 1 mV seem to apply to both voltages. So 200 or 100 ppm ( = 1 mV / 10 V) of uncertainty for the 2 voltages.The first table is for ref. voltage modules/PCBs that are individually measured / trimmed, not the bare reference chip.The Ref. IC table has some entries shifted to wrong tables.The data are also a bit old - prices generally went up quite a bit and there are newer parts available now (e.g. ADR1399)

author: klimm
author_rank: Contributor
timestamp: April 30, 2025, 11:12:25 am
content: Thank you Kleinstein,so I managed to compute the wrong way. This was my lesson for today as I was not able to find the way to compute ppm.I am aware that the table has ref modules but I had no info about these but the DS

author: jwet
author_rank: Frequent Contributor
timestamp: April 30, 2025, 07:56:41 pm
content: Quote from: BravoV on October 01, 2015, 05:11:04 amI was Director level apps guy working in standard products at Maxim when these were designed. This was after most of our delivery problems of the early 90's were behind us but there was still some ill will in some corners.They are really nice references for their time and intended use. They have a lot of innovative curvature correction and other technology in them- unfortunately, Maxim didn't do a lot of ISSCC papers, etc, just not our style. They were sort of a "shoot the moon" kind of part to see what we could do with our best processes and ideas within a marketing envelope of intended customers. We put one of our best designers on it and had few constraints about process or die area to first order. The project created a family of refs that range from 5 ppm to .5 ppm in a range of prices and improved our internal infrastructure for reference design- they require a lot of long term logging and temp cycling. We weren't shooting for "Super Referenece" territory like the LTZ etc. The intended application for these parts was industrial automation in 16 to 20 bit data converters in high-end modular PLC's from guys like Allen Bradley and Siemens. Modern industrial SCADA uses a lot 16 bit converters but seldom use reference much better than 10 ppm/C. The banner spec for their customer is 16 bits and they don't look at corners. We were trying to make compelling parts for this market. Its by far the biggest dollar volume market for refs. These sold very well in that market. We didn't even show them to the Agilent's and Keithley's- not a lucrative market and somewhat well serviced by the parts referenced here.The problem with designing high performance references is its not a very good "business". They are initially difficult to design using up your very best designers, take tons of time to characterize and correlate models with behavior and only a few devices are really required at the very high end. They also have long wafer test times for binning and then long trim times that usually involve temp slews. The other problem is at the 6.5 digit level, the existing solutions are excellent. Its interesting now that ADI has acquired LTC and Maxim and already had their own super references if they are paying attention any more.I'll follow this thread too.

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 01, 2025, 08:04:29 am
content: For checking all my casual DMMs I use affordable ADR01 with 0.05% grade (simple self-designed device without any heaters). It's good enough for me, I guess. It's quite good and simple so there is no need to buy it (or AD58x module) from China.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: May 01, 2025, 09:14:03 am
content: my favoriteLTZ1000LM399anything "under" that i consider waste of time playing with

author: Andreas
author_rank: Super Contributor
timestamp: May 02, 2025, 01:25:03 pm
content: Hello,the AD586LQ (CERDIP-Package)and AD587 in CERDIP Packageare also good long term stable devices (after some run in phase)Unfortunately I never managed to get a MAX6350 in CERDIP package.(the plastic package suffers from humidity changes)with best regardsAndreas

author: klimm
author_rank: Contributor
timestamp: May 03, 2025, 07:43:46 am
content: Good enough to use with ICL7135 in a 4.5 digits voltmeter ?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 03, 2025, 08:02:56 am
content: A 4.5 digit meter is usually not yet that demanding to require a high end reference. Quality wise I would consider a max6070 or similar. The ICL7135 and similar ADCs have the slightly tricky point that they want a trimmable 1 V or 0.1 V refererence, as the adjustment is usually via the ref. voltage. So the point can be looking for a 1.024 V ref. like MCP1502-10 to simplify the trim if a 1 V ref. is used.

author: klimm
author_rank: Contributor
timestamp: May 03, 2025, 08:26:02 am
content: Thank you for the advice I took note of this,I do have 2 AD 588BQ and was thinking to put one to use getting 1V with a divider/ buffer of course that will cost something.

author: iMo
author_rank: Super Contributor
timestamp: May 03, 2025, 09:37:16 am
content: Quote from: klimm on May 03, 2025, 07:43:46 amFYI - I have here a bunch of +/-1.9999V ICL7135 based modules (called "UP-413", year 1997, sold by Conrad) and they use LM358-1.2V reference trimmed to 1.0000V by a 10t trimmer..PS: even it works surprisingly well, I would use a better reference in the module, but still the trimmer may spoil the fun..

author: Kleinstein
author_rank: Super Contributor
timestamp: May 03, 2025, 10:01:39 am
content: The ref. input of the ICL7135 is high impedance. So no buffer needed.

author: iMo
author_rank: Super Contributor
timestamp: May 03, 2025, 10:18:04 am
content: The issue is the 1.0000V you would need for the ICL7135's reference. Unless you will calibrate it in software by an attached MCU (reading the ICL's outputs) you have to use a divider and a trimmer around the reference. So you have to consider the TC and the long term stability of the reference as well as of the resistors and/or the trimmer.

author: klimm
author_rank: Contributor
timestamp: May 03, 2025, 10:23:31 am
content: I've seen some modules using 1N829, or LM336 refs. They use a trimmer parallel on the zenner to trim the right voltage. Not happy with that for a voltmeter expected to have a useful accuracy and precision for 4.5digit.Just wonder if I choose a resistor divider to get my 1V from the 588BQ is it better to first use the internal op amps/divider to get 5V and only then apply another divider or go directly with 10V.Would be 0.1tolerance divider resistors, 50ppm ok? Can't afford very accurate ratio resistors as Caddock.

author: iMo
author_rank: Super Contributor
timestamp: May 03, 2025, 10:34:16 am
content: The optimal solution is a quality reference in metal or ceramic, giving 1.024V or 1.2V output fed to the ICL directly, and making the calibration and temperature compensation of the entire stuff in software (an MCU reads the ICL).With 50ppm/C resistors around the ref and a 50ppm/C reference the "1.9999V" at the display will vary by perhaps max +/-2 counts/C, imho (not counting the ICL's TC and noise and the long term stability of the parts especially the trimmer).So - in order to see a "stable reading" within say 10deg Celsius temperature band you would need something like <1.25ppm/C resistors and <1.25ppm/C reference (not counting the ICL's TC and noise and the long term stability of the parts especially the trimmer).

author: klimm
author_rank: Contributor
timestamp: May 03, 2025, 10:47:11 am
content: Thanks,I want to avoid an MCU for a simple 4.5digit DC voltmeter the way Keythley did with their 178DMM.This project should actually replace a 3.5digit multimeter that must be refurbished or replaced. I like the sturdy case and well insulated transformer(40 years) and thought I will use this pretext to learn about ADC and possible troubles so I will invest no too much.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 03, 2025, 11:16:57 am
content: For the AD588 the main outputs to consider would be the 10 V or manyby the NR pin for the raw zener voltage. A divider of 1:9 is reasonable available, e.g. as DIV23 or from 6 resistors (as 3p:3s) of an NOMCT array. 6 resistors from the same batch could also work OK.For the fine trim the point is to have little effect from the trimmer. One way is to have the trimmer across the full voltage and than use a series resitor to the wiper to reduce the effect on a fixed divider.

author: iMo
author_rank: Super Contributor
timestamp: May 03, 2025, 12:31:39 pm
content: The resistor from the wiper should be of a pretty large value one - as the wiper's contact resistance is the major source of parasitic fluctuations and TC, afaik (and the trimming range should be small).For example the NatSemi++ in their 399 datasheets shows 100k trimmer across the full voltage of the reference output and a 2Meg (I would go even higher) one from the wiper to the input of the output opamp buffer (and to the mid of the divider).Now, the question is what should be the divider's resistors values in order you can trim down say +/-30mV at the divider (wired to ICL's input).Perhaps we have to fire up the LTspiceQuote from: Kleinstein on May 03, 2025, 11:16:57 am