Accurate voltage / current / resistance reference. PentaRef and DMMCheck

[mjlorton]

I came across these devices from VoltageStandard.com thanks to SamGab.

They have proved to be a great resource for doing reference /  accuracy checks during my multimeter reviews.

More detailed info on them:
http://www.voltagestandard.com/DMMCheck.html
http://www.voltagestandard.com/PentaRef.html

I'm keen to know if there are any other devices out there that other folks are using that are reasonably priced to perform these functions?

My video review of the DMMCheck and PentaRef:

Cheers,
Martin.

[Rerouter]

Great Video,
was chuckling to myself about how the cheaper meter was outgunning the fancier meters worth hundreds each

still i have to ask, where you at 70 degrees F when you did this video :/

[EEVblog]

That reminds me, I shot some video a while back on a resistance standard I built, but haven't released it because it's, well, not that exciting!
About as much fun as a $20 resistor in a box with banana plugs :->

Dave.

[mjlorton]

Great Video,
was chuckling to myself about how the cheaper meter was outgunning the fancier meters worth hundreds each

still i have to ask, where you at 70 degrees F when you did this video :/

Thanks,

No, it was about 75 F...it's been a tad warm in Cape Town this summer and that was a cool day. Although Voltage Standard do quote what offset to expect per degree F, I plan to run some tests with varying temperatures to see what effect they have on readings.
Cheers.

[Rerouter]

i believe from the documentation you where showing at the start, it was 15uV per degree F or C, (no i didnt rewatch for that, my memory just has its moments)

[saturation]

I don't think anyone has done as thorough a  review of the these low cost voltage references so you may be the first.  IIRC the only other person out there selling a low cost reference is Geller's SVR.

You take great videos, congratulations. 

Dave showed in the older eevblog DMM shootouts, many low cost meters can read as well as, or better than big name DMMs.  A bigger question is reading consistently and continuously with age or subject to field conditions of humidity, heat, cold, or even physical abuse, that's the extra one pays for in costly meters.

May I suggest you subject the winner to a simple torture test with the Fluke: put both it and the Fluke in a refrigerator, do some measurement tests, then either in a metal box in sunlight [ or carefully in your oven, just try to get them to reach an ambient temperature of 120F] then spot check their readings.

[IanB]

My video review of the DMMCheck and PentaRef:

Interesting, but it was hard to stick it out for the whole 45 minutes. I think you could up the pace a bit by editing it down and talking a bit faster. About 15-20 minutes would be a good length for that amount of material.

I was looking for two things you didn't do. I was looking for you to show or mention the zero scale reading of the meters with shorted probes just to make sure they didn't start out with any zero offset. Rel'ing out any zero offset is important especially on lower ohms readings. Also I cringed when you were free holding the probes against the contacts. Clipping the probes on and letting go would give a more stable reading and reduce the effect of contact resistance.

[tinhead]

Interesting, but it was hard to stick it out for the whole 45 minutes.

indeed ...

I was looking for two things you didn't do. I was looking for you to show or mention the zero scale reading of the meters with shorted probes just to make sure they didn't start out with any zero offset. Rel'ing out any zero offset is important especially on lower ohms readings. Also I cringed when you were free holding the probes against the contacts. Clipping the probes on and letting go would give a more stable reading and reduce the effect of contact resistance.

oh well, that's why he made second 45min video ^^ ...

[mjlorton]

I don't think anyone has done as thorough a  review of the these low cost voltage references so you may be the first.  IIRC the only other person out there selling a low cost reference is Geller's SVR.

You take great videos, congratulations. 

Dave showed in the older eevblog DMM shootouts, many low cost meters can read as well as, or better than big name DMMs.  A bigger question is reading consistently and continuously with age or subject to field conditions of humidity, heat, cold, or even physical abuse, that's the extra one pays for in costly meters.

May I suggest you subject the winner to a simple torture test with the Fluke: put both it and the Fluke in a refrigerator, do some measurement tests, then either in a metal box in sunlight [ or carefully in your oven, just try to get them to reach an ambient temperature of 120F] then spot check their readings.

Thanks for the comments and feedback.

I have done one set of tests in a freezer but that was before the DMMCheck and PentaRef arrived...I'll add the next set of temperature testing to my job jar.

Cheers,
Martin.

[Circuitous]

I don't think anyone has done as thorough a  review of the these low cost voltage references so you may be the first.  IIRC the only other person out there selling a low cost reference is Geller's SVR.

I have a PentaRef (bought in Novermber 2011), and the Geller SVR  (received on 2/13/12). http://www.gellerlabs.com/SVR%20Series.htm The PentaRef is quite nice, and seems to be very stable. It raised my suspicions about my BK 5491B meter's accuracy in the 5 and 50V ranges. In November, with my PentaRef set at 10.0000 volts, the meter read 10.017 volts.
When I received the SVR last week, I retested my meter using the PentaRef, and got a reading of 10.017 volts (same as in November). I then used the SVR, getting a reading of 10.018 volts, reversing the leads gave a reading of -9.982 volts).  More on this thread: https://www.eevblog.com/forum/product-reviews-photos-and-discussion/bk-5491b-dc-accuracy/

Currently, I don't have a meter with enough resolution and accuracy to fully test the Geller SVR (but, maybe in a couple of weeks I will).
Where as the PentaRef is powered by (2) 9-volt batteries, the SVR needs a 15V external supply.  I used my bench supply and fiddled with the voltage a bit just to check the stability of the output.  The stability was perfect (per my lowly  meter), but I didn't write anything down; so, I'll have to re-run those tests and post a follow up.

[IanB]

I considered buying a Geller SVR, but was deterred by the web site. It is confusing and muddled, and offers no easy way to actually purchase the device. The required purchasing information is scattered over different parts of different pages. There's no single place that tells you what you need to know in plain English--you have to solve a puzzle before you can buy the thing. I think they must be losing many sales from the poor quality of their store front.

[muvideo]

I considered buying a Geller SVR, but was deterred by the web site. It is confusing and muddled, and offers no easy way to actually purchase the device. The required purchasing information is scattered over different parts of different pages. There's no single place that tells you what you need to know in plain English--you have to solve a puzzle before you can buy the thing. I think they must be losing many sales from the poor quality of their store front.

You are right but i contacted him/them on ebay and he/they were very helpful and responsive, I bought 2 units,
one calibrated to 20°C and one other to be assembled by me to be used as spare.
I built also a pair of ovens for them.

Fabio.

[saturation]

Yes, he's more an EE than a salesman.  I have had many email exchanges with him and he is happy to discuss whatever you need to have done when you buy one of those SVR.

Geller's site does have fairly more technical information on how he calibrates his units, and you'll have to take the description to consider if a short term accuracy of 10ppm is viable, preferred mostly for 6.5 DMMs, compared to Malone references.  If you're working with less accuracy, it may not be an issue.

http://gellerlabs.com/SVR%20Series.htm

http://www.voltagestandard.com/New_Products.html

For better results, the standard for calibrating references to 10 ppm is ~ 10x better, or 1 ppm, which is what the Fluke reference can do.  Malone's calibration 25 ppm, a bit low for $180 price. The effect of shipping the SVR to an owner unpowered has risks.  Lastly, its more common to use 10V in metrology work, not 5V.

I considered buying a Geller SVR, but was deterred by the web site. It is confusing and muddled, and offers no easy way to actually purchase the device. The required purchasing information is scattered over different parts of different pages. There's no single place that tells you what you need to know in plain English--you have to solve a puzzle before you can buy the thing. I think they must be losing many sales from the poor quality of their store front.

[Circuitous]

I had hoped that tonight I would post some detailed measurements (6 1/2 digit) of my PentaRef and Geller-SVR voltage sources, using the new Agilent 34410A that was to be delivered today.  Unfortunately, Tequipment.net put an old 34401A in the box instead... their second mistake in as many months.  Maybe I'll have something by next weekend.

[mjlorton]

I had hoped that tonight I would post some detailed measurements (6 1/2 digit) of my PentaRef and Geller-SVR voltage sources, using the new Agilent 34410A that was to be delivered today.  Unfortunately, Tequipment.net put an old 34401A in the box instead... their second mistake in as many months.  Maybe I'll have something by next weekend.

Pity...but look forward to your post and findings.

[muvideo]

Maybe I can give my contribute to this discussion here.
The equipment I have:
2 Geller SVR, one calibrated to 20°C and the other not calibrated,
both mounted in thermoregulated ovens built by me.
1 5 1/2 digit fluke 8520 that I'm repairing but seems to function properly in DC Voltage mode
1 6 1/2 digit solartron 7060 functioning but not calibrated
some other handhelds, one with 4 1/2 digits, others with less resolution.
I can monitor the gellers temperature visually and with PC trough DS18B20 sensors.
I hope I'll have in my hands another high resolution meter, but I don't know if it will fully
functioning.
At least I can make relative measurements on temperature and input voltage response.

In the spare time I can build a test procedure with your help.
So if somebody has test proposals I'm ready to follow your instructions.

Fabio.

P.S. More details:
Here the ambient (and my lab's) temperature is rising daily, now it oscillates between 5-8 at
night and 10-14 at day. It will be higher in the spring.
The multimeters are not calibrated but:
- the calibration of the fluke were never touched and it measures very close to 10.0000 from 10°C to 18°C
ambient (calibrated SVR at 20°C+-1°C), it's reference uses a "motorola" (fluke special part?) sfa263
buried zener+ transistor, as I understand very similar to the circuit built in the old fluke reference like the 731.
- the solartron calibration was messed up by me, it wanders quite a bit with temperature, it moves
by as much as 30ppm or more from 10 to 16°C, I'm waiting to have 20°C room temperature to zero it
on the calibrated Geller SVR, it uses a discrete zener diode as reference.
- the calibrated Geller SVR was continously powered on at 20°C  from when I mounted it in the oven, about a week
after I received from the postman last month.

[saturation]

Making Conrad Hoffman's chopper amp is another option; getting a low cost confirmation of its measurement by mailing it to Geller or voltagestandard should confirm your settings.  It has the same basic design as the EDC MV106, see eevblog's review video on it.

http://conradhoffman.com/mini_metro_lab.html

Conrad is also on the forum if you want to pm him.

[Vredstein]

Got a DMMCheck last week. Tested a UNI-T UT61E that's also a week old. Tested at 72 deg F.
DMMCheck has a 5V DC reference, 0.9995 mA reference, 99.97k, 9.991k, and 999.2k resistors. All tests performed twice using Fluke probes.

5 volt standard
autorange                 4.992 volts     
range#1                    OL
range#2                    4.992 volts
range#3                    4.98 volts 
range#4                    4.9 volts

0.9995mA reference
Selector on Amps
auto=0.001
manual range is disabled
Selector on mA
auto=0.995mA
manual range 1=0.995mA
manual range 2=0.99mA
Selector on uA
auto=1000.3uA
manual range 1=OL. plus audible beep
manual range 2=1000.0uA

                          99.97k resistor                                     9.991k resistor                       999.2k resistor                                                auto                            99.77k                                            9.971k                                                  0.9961
range 1                       0.07M                                               0.00M                                                   0.00M
range 2                       OL                                                     OL                                                          OL
range 3                       OL                                                     OL                                                      0.9961                       
range 4                       OL                                                   9.971k                                                 0.994k
range 5                       99.97k                                             9.93k                                                   0.97k
range 6                     0.0994M                                           0.0096M                                               0.0007M
range 7                     0.07M                                               0.007M                                                 0.000M   

Also tested a used Fluke 87 I got on Ebay last week. The unit is 23 years old and closely matched the DMMCheck for all functions.   
5.00 volts on auto range, 5.000 volts on 4 1/2 digit mode, 0.995mA on auto range, 99.90k, 9.99k, .9993M ohms             




                             

[Tooms]

That reminds me, I shot some video a while back on a resistance standard I built, but haven't released it because it's, well, not that exciting!
About as much fun as a $20 resistor in a box with banana plugs :->

Dave.

Now you have record it can we see it.


Tooms

[amspire]

For better results, the standard for calibrating references to 10 ppm is ~ 10x better, or 1 ppm, which is what the Fluke reference can do.  Malone's calibration 25 ppm, a bit low for $180 price. The effect of shipping the SVR to an owner unpowered has risks.  Lastly, its more common to use 10V in metrology work, not 5V.

The $180 is not a bad deal. It uses a Thaler hybrid reference IC that outperforms all of the monolithic reference ICs currently available. When Thaler owned the company, these chips were far more affordable, but now Cirrus owned Thaler, the prices jumped up many times. Last time I looked, I was seeing prices like $70.

The specs quoted are for 6 month accuracy , and a +/- 6 deg F temperature variation and a 8V input supply variation and I think they are conservative specs. The actual 1000 hour stability of these chips is typically 6ppm, so if you new the temperature and supply voltage that the reference was calibrated at, it would typically be within 7ppm after 6 months. The chips could easily drift a lot less by the end of 2 years.

The price includes recalibration for 2 years, so i think $180 is OK.

5V instead of 10V? not sure if it matters much. If you are calibrating s 59999 full scale meter, 5V is useful. 10V is only 1/6th of full scale - pretty useless. Whatever you have, you will need to scale it eventually to the voltages you need. you just need a starting point.

Richard.

[saturation]

Yes, I'd see your point depending on what it costs in your area to get calibration and the cost of hardware.

eBay items change the field, so some thoughts. 

A well bidded for 3456a is typically  ~ $100 and, in USA, commercial calibration another $100; all those prices include shipping a heavy DMM.  HP's data gives us a DMM accuracy of ~ < 25 ppm year.    You can use it to measure stable but uncalibrated sources to compare your other meters.  In a more traditional way, the EDC MV106 reference Dave reviewed has similar accuracy as the $180 reference, and in November, 2011, was as low as $50, uncalibrated.  +$100 for formal calibration and you have a calibrator that scale VDC with nV resolution.

But shipping eBay items overseas, can cost more than the item,  not to mention your local calibration costs, so a compact, albeit limited source has appeal.

Finally, theoretical concerns.  Since we are paying the extra money to obtain higher accuracy, were more uncertainty exists, the technique of calibration has to defined a bit more so we are less uncertain about our uncertainty  . 

For example, at 25ppm accuracy for $180 reference, the preferred reference to calibrate with TUR of 4:1 is ~6 ppm accuracy.

The basic 3458a has accuracy at 10 V: 0.5ppm/24h, 4.1 ppm/90 days,  8ppm/1 year,  14ppm/ 2 years.

To adjust his reference with less uncertainty they need a 3458a at < 1 yr spec for its 10V range.  Is this certificate statement for a 1 year or 2 year cycle?

http://www.voltagestandard.com/Home_Page_JO2U.html

Geller's method of adjusting 10V using a 732a is less uncertain because his source is better.  The 1 yr rating of 732a is 3ppm and has a 1 year cal cycle.

http://gellerlabs.com/Voltage%20References.htm

For better results, the standard for calibrating references to 10 ppm is ~ 10x better, or 1 ppm, which is what the Fluke reference can do.  Malone's calibration 25 ppm, a bit low for $180 price. The effect of shipping the SVR to an owner unpowered has risks.  Lastly, its more common to use 10V in metrology work, not 5V.

The $180 is not a bad deal. It uses a Thaler hybrid reference IC that outperforms all of the monolithic reference ICs currently available. When Thaler owned the company, these chips were far more affordable, but now Cirrus owned Thaler, the prices jumped up many times. Last time I looked, I was seeing prices like $70.

The specs quoted are for 6 month accuracy , and a +/- 6 deg F temperature variation and a 8V input supply variation and I think they are conservative specs. The actual 1000 hour stability of these chips is typically 6ppm, so if you new the temperature and supply voltage that the reference was calibrated at, it would typically be within 7ppm after 6 months. The chips could easily drift a lot less by the end of 2 years.

The price includes recalibration for 2 years, so i think $180 is OK.

5V instead of 10V? not sure if it matters much. If you are calibrating s 59999 full scale meter, 5V is useful. 10V is only 1/6th of full scale - pretty useless. Whatever you have, you will need to scale it eventually to the voltages you need. you just need a starting point.

Richard.

[bubucis]

MV106 seem to be much more expensive on the eBay.
http://www.ebay.com/itm/EDC-Krohn-Hite-MV106-DC-Calibrator-/360290886744?pt=LH_DefaultDomain_0&hash=item53e302a458#ht_500wt_973
I also have seen some around $300, but nothing below $100.

I recently bought AN3100 that is similar to MV106, but with lower 50 ppm accuracy for $ 130, and there was a lot of biddding for it.
http://www.eserviceinfo.com/index.php?what=search2&searchstring=AN3100

It actually turned out to be still in spec after all these years when compared to the Geller SVR using 3456a ration function.

Also 3456a seem to have gone up in the price:(

must be eevblog influence

It does look that Geller combined with one of these voltage standards have better specs than PentaRef.

[saturation]

Patience is rewarded by great buys.  It took me 1 year to find 4 HP3456a all under $100 delivered and another year for the EDC.  When it appeared at $50 I just snapped it up.  The seller raised his price as each one of the 5 he had sold, topping at $200.  Still cheaper than the linked one at $1200.

http://www.ebay.com/itm/220911189190?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Check for model variants too built similarly and hunt for those series numbers: MV 105, 116, CR103 etc.,