Cheap eBay AD584 Voltage References - My experiences

[intabits]

@intabits: Have any of the reference boards you've bought deviated significantly from each other?  I'd just like to be able to calibrate my 4.5 digit DMMs well enough that I'm within 1% for general lab use.  Maybe the typical reference is good enough for that without a cal certificate?

Sorry, didn't notice that this was directed at me.

At least for the units I have, I'd say they should be easily good enough to get a 4.5d any DMM to within 1%.

As to deviations, I haven't done much with mine except for this:-


Which is a mess that I've been running for year now.
It's made almost entirely out of ebay crap - I just wanted to get something logging away...
It consists of:-
1/  Two large hot-swappable LiFePO4 battery packs, powering:-
2/  An Arduino UNO with a data logging shield (RTC & SD card).
3/  A DS18B20 temperature sensor, plus a DHT11 (temp and humidity sensors)
4/  A REF5040 providing 4.096V to:-
5/  A cheap ADS1115 module (4Ch 16 bit ADC), which converts the output of:-
6/  2 of the AD584 modules
7/  2 eBay "LM399"s (outputs are divided by 2 for the ADC)

It logs timestamp, 2 temp, 1 humidity, and 4 VRef readings every 10 seconds (way too often, but storage is cheap).
It's sitting in my back junk room, where it collects a lot of dust, and is well exposed to the elements (near an open window, and a doorway that is almost open to the outside)

Below is the full year output (DS18B20 temp and the VRefs). There are a few glitches, and a month of missing data that I'm still kicking myself for losing.
Obviously, my software also needs a *lot* of work.
The strong upward trend (and a lot of other variation) I put down to the crappy ADC. But it can be seen that the 4 VRefs track each other quite well, and the two AD584s are nearly always with an LSB of each other.


This can be seen better here, which is 10 days in the middle of the above. 


At some stage, I'm hoping to do some analysis of all this, trying to see what correlates with what. Next version will use a better ADC (and maybe two, with one kept further away from the environmental changes)

[GregDunn]

That's quite impressive - in spite of large ambient temperature swings, they all seem to be pretty stable.  And, as you say, tracking is really good.  I appreciate you sharing that data!

I hope to have another test run when my other references arrive (assuming they all have cal sheets).  One of them is an LM399, and they're all supposedly aged.  I won't be able to log data as completely as you did, but given that my temperature is essentially constant I think I can get away with fewer samples on a long term test.  It will be interesting to see the meter variances, if any, on a single reference and the differences between references with all the meters hooked to it.  Depending on what I see from the other references, I may be able to tell which meter is most accurate.

[intabits]

Made some minor updates to my previous. Most importantly, I'd left out of the BOM, the REF5040 providing 4.096V to the ADC. Thus each LSB is 125uV.

Since the the two AD584's match each other to with a couple of LSBs on the 2.5V output, over a wide time, temperature and humidity range, I was wondering if similar applied to the 5.0V, 7.5V, and 10V outputs.
If so, using two with a floating power supply, they might provide a very stable 2.5V reference between the 5V of one and the 7.5V of the other.
All the common mode environmental issues would be cancelled out...

[GregDunn]

Now I have two AD584 references: one the KKMOON branded item off Amazon (claimed checked with a 34401A), and a generic AD584 off the Bay (the one with SMA connectors for the outputs as well as edge connector pins; Fluke 8846A reference meter).

I ran the KKMOON for a solid 24 hours after warmup (temp was about 23.7-24.0C) and all I ever saw was the typical ±1 LSD display error from any of my meters.  It was listed as "10.00325" on the hand-written sheet.  My Keithley 197a registered... 10.0037 and the Fluke 8600 and Dana 4200 were pretty close.  Here are the deviations I read vs. the supplied data:

Keithley: +0.0045%
8600A: +0.027%
8800A: -0.0015%
Dana: -0.009%

Now, the generic AD584.  Only about 3 hours of warmup so far, but I strongly suspect this won't change any further.  It's been solid since about 5 minutes after power-up (meters, of course, warmed up overnight first).  It had the printed cal data, but all the listings of this seller showed different values so if not actually measured, they tried to be creative.  However, after measuring the 10.00260 pin with the Keithley, I got... 10.0027.  Deviations from supplied data:

Keithley: -0.0010%
8600A: +0.024%
8800A: -0.0015%
Dana: -0.0060%

I have no idea what the "real" values of the references are, but after seeing that the meters all cluster around the written values with very small std dev and variance (yes, I actually calculated them.  Nerd.) , I'm impressed.  I would not have been surprised to see them all read higher or lower than the reference, given the low variance.  Oh well, here's a few data points for the forum at least.   

Edit: added the new 8800A/AF measurements and corrected a calculation.

[myf]

Hello,

I hope I'm posting in the right place.

I am looking for a cheap voltage reference and I do not have access to a 7.1 / 2 digit multimeter.

I have an inexpensive 4.1 / 2 digits multimeter uni-t 61E. Maybe I'll buy another 4.1/ 2 or 5.1 / 2 digits multimeter later.
I want to control my multimeters. Are all the numbers correct?

Are these AD586 with their own calibrated sheet sufficient for this purpose?
Is one device enough, or are there a lot of funny experiences that require 2 or 3 devices?

Which vendors deliver everytime the device with this genuine calibrated sheet on ebay.com or aliexpress.com?

On eBay, I find this article at around 10 €. Is it fair and serious, or do you know other cheaper ones?

http://www.ebay.co.uk/itm/AD584-Precision-Voltage-Reference-2-5-7-5-5-10v-Calibrated-By-Agilent-34401/261972330425

For search, the article number is 261972330425.

What are your advices?

Have a good day !

François, from France.

[GregDunn]

I have only tried one eBay vendor, and fortunately they shipped the unit with a cal sheet.

Unfortunately, I don't think anyone has found a vendor which is certain to provide cal data.  I bought the KKMOON branded Amazon unit

https://www.amazon.com/gp/product/B00Z033Y6Y/

and a board from the following vendor:

https://www.ebay.com/usr/vrg5612

But while I'm reasonably certain the Amazon unit will come with a cal sheet, there's no guarantee any eBay vendor will provide one.  I just took a chance and it worked out.

[Kosmic]

Which vendors deliver everytime the device with this genuine calibrated sheet on ebay.com or aliexpress.com?

Even if they give you a calibration sheet, you really think you can trust them ? Even if they took the trouble of taking some measurements you don't even know if their meter is calibrated.

I don't think those board are more accurate than the chip sitting on them. So you should look at the specsheet of the AD584 et AD586 and decide if the accuracy you get out-of-the-box is enough for you. Ex the AD584J is 10V +- 30mV.


If you want more accuracy you should look for other more expensive products (ex DMMCheck Plus voltagestandard.com or the 10V ref from FisherInstruments.com)

[Harfner]

I bought this unit https://www.ebay.de/itm/AD584-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-AD584JH/153094942682?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

It does contain an AD584JH with a datecode from 93 and 4 resistors. On the back are values written by hand supposedly measured from this board. The voltages are measured to 4 1/2 digits, the resistances to 5 1/2 digits.

I checked with a HP3478A and a Prema 5000, both several years out of calibration. If I assume both meters to be within 200ppm (their 1-Year limits are 120-150 ppm), than the values are genuine.

[GregDunn]

I should probably add that I acquired a third reference, though this one is an LM399-based board with a noticeably different "cal" value.  The values read off my meters all cluster closely around this one too, though with a slightly higher std. dev. value.

In all three cases, the mean of the measurements is within 0.01% of the written value given for the reference board.  Is it possible that randomly picked digits give a number which is the mean of a tight cluster of values given by my meters in all three cases?  Of course.  But I believe they were actually read off a high precision meter, of unknown calibration heritage.  The fact that my meters (all of wildly different ages, design and use history) agree within a small fraction of a percent to the written values gives me some confidence that the values on the stickers were obtained in good faith, no matter their absolute accuracy.  The whole point of calibrating them (if done with a traceable reference) is to get an idea of what the actual voltage is - you already know it's not going to be 10.000000V.

And, if they're aged, the accuracy is less important than the stability.  Even the worst AD584 is spec'ed at 25ppm long term drift - on the same order as the output noise.  The LM399 is much better than that.  Good enough to at least ensure that the value, whatever it is, doesn't drift far enough to cause a problem on any of my meters.  They're clearly all inadequate to use as a transfer standard for something like a 3458A.