VoltageStandard.com - Low cost Voltage References

[sonicj]

these look really handy for those w/o access to precision references. voltagestandard.com



the dmm check is only $32.50 with free re-calibration for a year and only $5 including return shipping after that. similarly low calibration deal for the other 2 models!

anyone here use one of these?
-sj

[Polossatik]

Hum, I don't think i'll really need it, but it would actually make sense to buy this with e few people in the same area and then use it to check your equipment.

What is the stuff with "2.048V, 2.500V, 3.000V, 4.096V,  and 4.500V references are also available" ?

why 2.048V and 4.096V ?

[alm]

There has been some discussion about this in the past on this forum, should be possible to find it by searching.

why 2.048V and 4.096V ?

DAC/ADC, 1 bit is a nice round number of mV (eg. 2mV/bit for 2.048V and 10-bit DAC).

[Mechatrommer]

whats the big inverted "U" shaped metals?

[sonicj]

whats the big inverted "U" shaped metals?

test clips

[Zyvek]

I have their REF5-01 Precision Voltage Reference unit  (5v standard) and it's a pretty good deal, this new model looks even better. 

[Simon]

really to calibrate a multimeter you should try and read a couple of values per range, even if it's an auto-range meter it will have ranges with associated circuitry that are automatically switched through. still if you need 5V spot on worth a shot

[slburris]

I've got their 5V only reference and like it.

For resistance it's possible to get 0.05% resistor
standards on Ebay for not much money, so that's
twice as good.

But if I didn't already have my 5V reference, I'd
probably go for this all-in-one unit.

Scott

[mikeselectricstuff]

Hum, I don't think i'll really need it, but it would actually make sense to buy this with e few people in the same area and then use it to check your equipment.

What is the stuff with "2.048V, 2.500V, 3.000V, 4.096V,  and 4.500V references are also available" ?

why 2.048V and 4.096V ?

So if used as a reference for a 12 bit ADC or DAC, you get 0.5mv and 1mv per count respectively. Probably used less nowadays that everything has a processor in it to do the scaling, but when test-gear hardware didn't have software in it, having a direct relationship between a binary number and a voltage could be pretty useful.

[sonicj]

interesting.

recently, i noticed my fluke 12 was off by about 2v at around 60v. i wonder what changed? i must have bumped it while cleaning or something even though i was careful to avoid the trim pot. idk... it seems fine now!
-sj

[saturation]

You may want to also read links here where voltage references are discussed in some detail:

https://www.eevblog.com/forum/index.php?topic=650.0

https://www.eevblog.com/forum/index.php?topic=601.0

Wanting to calibrate your DMM and having a stable reference are 2 different reasons. 

First, off the reference.

These little boards are better called voltage references, not standards, because they are not used as a primary measure by which volt, amps or resistance is compared, rather to reference your DMM against another after the same board has been calibrated against a better DMM.  There is only one volt standard, the josephson junction volt, which all other devices are referenced against.  There are also standard resistors you can purchase, but they too can drift over time, and its absolute  value has to checked against a NIST certified lab.  I think the amp is simply derived, once a you have a calibrated volt and resistance made, given ohms law.

For home use, making and maintaining a voltage reference is a very involved affair, its a combination of statistics and electronics.  Every reference is individualized because how they vary in the extremes of accuracy are very sensitive to the physical age of your device, assuming you keep the environmental conditions of temperature, pressure, and humidity, in order or importance, stable during calibration and measurement.

If you have a DMM with a ratio mode, like an HP 3456a, once you have a stable reference, you can use the ratio mode to generate a stable voltage from any good adjustable power supply ratioed against the reference board, so you can generate reference voltages above or below, say your 10.000 000 V standard,and hold it accurate to the uV.  This is a cheap and simple way to get reference voltages above those of the board you just bought, assuming you have a DVM like a 3456a; also how good your power supply can hold uV levels is a testament to how good your PSU really is.

Although resistor tolerance is the first thing one thinks off when buying a resistor to use as a reference, its actually its aging and tempco drift characteristic that is more important.  Tolerance simply means if you buy a 1k ohm resistor with .01% tolerance, that actual value you receive is +/- 0.1 ohm, so the real value you have can be measured somewhere between 999.9 and 1000.1 ohm.  Unfortunately, this means your resistance range can be no more accurate than .01%; the simplest thing and cheaper, is to buy a set of resistors with good aging and tempco characteristics and actual measure it against a NIST certified DMM and then note the true resistance and the environmental temperature of the measurement; what happens after that is then subject to temperature drift and aging; you needn't buy a high tolerance resistor which often can be expensive.

[Simon]

of course in theory you need to have your "reference" calibrated at least once every two years, or buy another one if it's cheaper 

[saturation]

Although that's a recommendation if you follow standard procedure from NIST and other metrological sources [every 1-2 years] what folks at volt-nuts have found experimentally is cheapo standards may hold calibration for much longer periods of time.

If you have an older Fluke 80s series, or older reference DVM like the HP3456a, its surprising these 10-30 year old rarely need adjustment, a formal calibration will simply reveal if they are in spec; assuming you measure them in a controlled environment.

The actual research papers, and this is a reason to join the IEEE if you are inclined, describe in detail the factors that cause calibrations to go off that you can correct for, however, these correction factors are never part of routine calibration procedures given to front line folks in industry.

If you were to take voltagestandard.com board or a Geller SVR board as is, without added procedures, you would send it back to them for recal periodically.

I've reconfirmed experimentally what research papers show, is the absolute ratings down to uV: 10.000 000 will vary with seasons due to ambient temperature, humidity and less so atmospheric pressure: so if you make a cal measurement that is not as precise as the day it was originally calibrated, it will be off in uVs, making you think its time for a recal.

You can control ambient temp and humidity in a lab easily, but its difficult to control for atmospheric pressure changes. You will have to put the voltage reference is a pressure controlled pot, with the internal pressure adjusted to maintain 1 ATA against the environmental swings, something not easy to make and I don't have. So, I log measurements at the same weather mBar my original measurements were made, controlling only temp and humidity in the lab.

All microvolt measurements assumes you know how to eliminate and control uV sources such as thermal, galvanic, triboelectric, ionic and static sources of voltage.  Simple things like using a copper test clip on a stainless steel measurement lug will create a galvanic source independent of other issues.  If test leads are not as the same ambient temperature as the DVM leads or the reference leads, you'll create thermal effects; if you touch the leads during measurement, it will create tribolectric or statics charges into the leads.

If you collect daily data on the reference, you can watch the uV levels swing in sync with the weather very linearly, you can actually predict how off it will be as a combo of temp, pressure and humidity.

Once you control for the environment and uV sources, the final source of drift is internal to the reference itself; if you let the unit age for 200 hrs+ before you send it out as a reference, it minimizes internal drift, but experimentally only references 1+ years old are stable will ne'er vary, except for those caused by environmental changes.

My solution was to buy 4 HP3456a: one 3456a is calibrate against a NIST standard, then calibrate the others against it as specific intervals using voltage and resistance sources that are accurate to ppm.  These measurements are then spot checked against the Geller SVR.  Each calibration was done at the start of each season for each DVM, but with the environmental conditions controlled, so one 3456a has been calibrated during the summer, fall, winter and spring.

The Geller SVR measurements are made to similar ambient temperature, RH and atmospheric pressure, and when rechecked for voltage, the same environmental conditions must be identical, before I log the reading.

9 months later, the SVR is still reading 10. 000 000 measured at the same conditions, although it has swung as high as 10.000 030V with weather variations.  The 4 3456a show no variations with weather, if the original calibration was done as precisely the same ambient conditions.  As these DVM are all over 15 years old, their internal references are aged, and should eliminate their internal drift; however, skeptical as I am, I am still tracking their responses controlling for weather, and just short of a year the internal reference is stable as well as the support electronics of the 3456a.

of course in theory you need to have your "reference" calibrated at least once every two years, or buy another one if it's cheaper  

[Jon Chandler]

Where I used to work, we had a large collection of accelerometers that were required to be calibrated on a yearly basis.  These were a variety of sensitivities from a variety of manufacturers.  Some of them were used often while others were never out of the drawer except for calibration.  There were calibrated at different times of the year, depending on when they were first calibrated.

It was interesting to watch the calibration results of the collection.  Sometimes they would all read slightly high for a period, other times slightly low.  Tracking results over the years, it became apparent that the "drift" seen in the group was actually drift in the reference accelerometer used for calibration.  By examining the results, we could tell when the metrology lab changed their reference!

Of course, this was the same lab that weighed one of the accelerometers for me when I needed the weight for a test procedure.  They weighed to with 0.1 once accuracy, and converted it to grams for me (around 90  grams)...with 8 significant digits!

[Kiriakos-GR]

I will just add this link .  

https://www.eevblog.com/forum/index.php?topic=1032.0

I bet that If you look on ebay , from time to time , you will get one like this.

There is no " Low cost Voltage References "  that can do multiple and accurate operations.  

And also , if your DMM gear are dirt cheap, why to have any calibration gear at hand ? .

The modern " low cost " DMM has less or none ability to get calibrated .
The only instruments that needs to be tested with Voltage References and resistors,
are the analog ones.

Not to say , that my own  100$ DMM ( the older of the many ) are still spot on after 15 years.

[kd5jha]

Actually,  when you are in the middle of a project ... Some times the worst thing that can happen to you is the cal lab people come by and grab your meter and calibrate it for you! If you are working with a very stable meter that happens to read consistently .0003 units off from your lab reference you can still use it because you can just mathematically correct for that inaccuracy. Stability is the most important carectaristic in a piece of test equipment... As long as it's wrong he same way every time it's still useful! If the cal folks sneak in and take it away to brainwash it you may have to start gathering all of your data again as you have  no way to know how stable it will be after a fresh calibration. When I worked in a lab, we did a few things to fight this issue... 1. When we bought meters we would get a whole batch at one time all with the same date codes and with NiST Cal paperwork... 2. We would characterize each meter as it came in and assign in a lab ID number (for check-in/out purposes) 3. We would put a sticker on the top of each meter with a list of correction factors to apply for each range for that meter. 4. All non trivial measurements were always made in a test jig with at least 2 meters minimum, critical measurements might be checked with 4 meters simultaneously. 5. Since we worked with high energy electronics, we had a confidence meter that was set aside for that purpose and that never went out for cal. It was never put in a live circuit where it could be damaged and was used as the labs comparison standard if another meter appeared to be drifting. 6 we also set up a field cal test jig that we used to check our meters for problems across all ranges, several values per range to give confidence in that correction factor.

This system worked rather well over the four years I was there, and we never had a problem with inconsistancy in any of our reports due to failing or drifting test equipment. Depending on a single piece of test equipment is about the worst thing you can do, cause it can drift without you noticing.

[saturation]

I couldn't agree more, its a reason beyond metcal, you can create a local standard on your own, with a judicious use of multiple meters and method to cross correlate them.

Most folks are satisfied with precision, accuracy requires much more of a meter that isn't obvious at face value.

Actually,  when you are in the middle of a project ...... <snip>
This system worked rather well over the four years I was there, and we never had a problem with inconsistancy in any of our reports due to failing or drifting test equipment. Depending on a single piece of test equipment is about the worst thing you can do, cause it can drift without you noticing.

[Mechatrommer]

sorry to bump. but i bought a voltage reference chip AD584JN that can provide 10.000V, 7.500V, 5.000V, 2.500V. isnt a single chip enough to make as a voltage reference?
ps: well err, 0.3% accurate only

[saturation]

Sure mecha, you can make a reference with that limited to its stability.  You'll need to characterize the chip to know what the final voltage is after you design it as a voltage reference and know it can swing +-0.3% thereafter.  The tempco drift is 30 ppm /C worse case, or 0.03 mV/C, which essentially is not noticeable since you'll need +100C to get the reference off 3mV from your starting point. 

As a reference you'll need at least one traceable calibrated DVM to measure output accurately
You need to age it for > 200 hours

I think its perfect to bump any old eevblog threads, electronics info doesn't become obsolete because of an old post, I see the archives as a reference, and less a transcript of old chats.

sorry to bump. but i bought a voltage reference chip AD584JN that can provide 10.000V, 7.500V, 5.000V, 2.500V. isnt a single chip enough to make as a voltage reference?
ps: well err, 0.3% accurate only

[Mechatrommer]

ok thanx. maybe 0.3% is enough for me. so far, i dont have any project that need to be accurate to few mV. i hope this chip will be handy and will be able to tell how far my cheapo dmm off based on the chip datasheet.

[Kiriakos-GR]

Basically the reference sources are useful only for  DMM's that haves 4+1/2 (5 digits) resolution or more ..

Always be careful , and buy the IC with the output that is supported by your DMM at 5 digits resolution.
Example : Your DMM it is 10,000 counts , do not buy anything over 8 or 9 Volts. 

For anything like 3+1/2 ( 4 digits) resolution, even the cheap LM7805 or any similar, 
its good enough as test gear. 

Simply because you can not see the extra digits , due the lower resolution of your DMM.

[fra.gherard]

there's something like this that i can buy in eu?
for the resistor check i can use foil resistor from vishay, but for voltage and current?

[HKJ]

there's something like this that i can buy in eu?
for the resistor check i can use foil resistor from vishay, but for voltage and current?

Why not buy from voltagestandard.com, they do ship to EU or did last time I bought something from them.

For voltage you can get a much more useful device from http://www.ianjohnston.com/ in UK, but it is also considerable more expensive.

[electr_peter]

One can buy from VoltageStandard.com directly, just contact seller by email. Even if buyer is from EU - no problem here.

I have used VoltageStandard.com services before. I was satisfied with communications, shipping and quality.

[fra.gherard]

how much did you pay for the postage?