Checking my DMM DC Voltage Accuracy

John`s Budget Gadgets

This just checks the low dc voltage accuracy which is in the ranges i use 99% of the time.

The Voltage Reference 2.5V 5.0V 7.5V 10.0V is set by just moving the jumpers look for "AD584 4-Channel 2.5v/7.5v/5v/10v High Precision Voltage Reference Module", and they only cost around $8 on eBay.

Checking the accuracy of my new UNI-T UT61E DMM on the low DC range.

I am running the Voltage Reference board from an 12v 1amp power adaptor from one of my battery chargers, they recommend using a battery for a more accurate result but i don't have any suitable battery`s




2.5V Below



5.0V Below



7.5V Below



10.0V Below

TinderBox (UK) said:

I am running the Voltage Reference board from an 12v 1amp power adaptor from one of my battery chargers, they recommend using a battery for a more accurate result but i don't have any suitable battery`s

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You could use a pair of 9V cells in series, or some coin cells - see the links here. The input needs to be at least 1V higher than the highest output that you use iirc.

Did they not supply a calibration certificate? Some AD584 can be a fair amount off, esp. the cheapest JH version (LH is the best).

It did come with this bit of paper, Great idea in the link about using 5x CR2032 =15V to power the reference.

The main IC on the board is "AD584LH1015"

John.

Gauss163 said:

You could use a pair of 9V cells in series, or some coin cells - see the links here. The input needs to be at least 1V higher than the highest output that you use iirc.

Did they not supply a calibration certificate? Some AD584 can be a fair amount off, esp. the cheapest JH version (LH is the best).

Click to expand...

John, did you calibrate your UT61e. I bought one to have a low cost quality meter and it did not meet specs on DC voltage. Tt was easy to calibrate and it is now within 2 counts on 2.5, 5.0, 7.5, and 10.0 volts. I checked all other functions and they were well within specs. Did yours have an English manual? Mine came with a Chinese manual, but I downloaded the English manual. I checked my Fluke 289 (several years old) and it had zero error on all five digits.

TinderBox (UK) said:

John`s Budget Gadgets

This just checks the low dc voltage accuracy which is in the ranges i use 99% of the time.

The Voltage Reference 2.5V 5.0V 7.5V 10.0V is set by just moving the jumpers look for "AD584 4-Channel 2.5v/7.5v/5v/10v High Precision Voltage Reference Module", and they only cost around $8 on eBay.

Checking the accuracy of my new UNI-T UT61E DMM on the low DC range.

I am running the Voltage Reference board from an 12v 1amp power adaptor from one of my battery chargers, they recommend using a battery for a more accurate result but i don't have any suitable battery`s

2.5V Below

5.0V Below

7.5V Below

10.0V Below

Click to expand...

Hi Bill

Mine came with 100% English Manual, My 61E seems accurate enough for me for home use now i can check it against the voltage reference, I bought an compatible data cable for the 61E for a couple of dollars i have not tried it yet.

http://www.ebay.co.uk/itm/111901886139?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

I also bought a panel meter for $5 soldered on a couple of probes and an 9v battery and i now have a small accurate low voltage dc meter, I would like to mount it in an box with banana plugs but that would more than double the cost.

http://www.ebay.co.uk/itm/262136732418?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

John

TinderBox (UK) said:

I also bought a panel meter for $5 soldered on a couple of probes and an 9v battery and i now have a small accurate low voltage dc meter, I would like to mount it in an box with banana plugs but that would more than double the cost.

http://www.ebay.co.uk/itm/262136732418?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

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Ah, so you also got the $5 MCP3421 0-4.3000-33.000V panel meter that I recommended earlier. One thing to be aware of is that its input impedance is a bit low at 350K vs. 10M typical (e.g. UT61E). This means it will draw about 30x the current of the UT61E when measuring voltage, e.g. about 30μA vs 1uA when measuring the voltage of a 9V battery. You can see the difference: the mV digit will decrease a few counts/min while measuring on the MCP but not on the UT61E. It also seems that its temperature coefficient is a bit high on the MCP, e.g. bumping the temp from 67F to 75F increased 22V by about 3.5mV, and 11V by about 1.5mV. Still it's a good deal at $5.

When I calibrated a couple UT61Es the best I could get was a constant error of 2-3mV too low across the entire 22V range, and there seems to be no way to adjust the gain to fix that. Perhaps this is the same behavior billcushman reported above.

I haven't had a chance to investigate the TempCo for the UT61Es. But I wouldn't be surprised if it plays some role in the oft-reported calibration drift (perhaps in combination with vibration-induced trimpot drift)

Gauss163, I could easily adjust my UT61e above or below the desired value. My unit was almost 13% low on DCV when received. This required a significant rotation of the multi turn pot. It is now within 1 or max 2 counts at 2.5, 5.0, 7.5, and 10.0 volts. I checked ACV,@120V, mVDC, capacitance, and resistance accuracy and linearity. All were well within specs. It appears that they forgot the DCV calibration. Since I calibrated it I have checked about 10 times over several days. It is usually ±1 count at all four check voltages.

@billcushman Thanks for sharing. Maybe more details will help to clarify my remarks about my UT61E calibration. First I calibrated so to minimize relative error, but I didn't like the result because the setting which achieved acceptable relative error on the low end forced the high end (near 20V) to be off by many counts = mV (about 5-7 iirc), even though it met the same relative error spec. So instead, I fiddled with it to see what it would look like if I calibrated it with the goal that the absolute error is constant across the whole range. This resulted in readings that were constantly 2-3mV low across the entire 22V range. So if I mentally add 2.5mV then all my readings are within 0.5mV. But that's a pain, it would be nicer to be able to implement that correction in the meter via a gain adjustment. But I don't see any easy way to achieve that. Anyone?

Both of my UT61Es behave exactly the same, so it may be possible that they all behave like this, or at least all from the same batch of certain components (ADC or Vref or precision resistors?)

I haven't had a chance yet to investigate the effects of temperature and vibration on the calibration.

It would be interesting to hear reports from others on these matters. If they do all behave the same then perhaps between us we can figure out the optimal way to calibrate them and workaround the limitations.

I too have more accurate and precise handheld DMMs (e.g. 500000 count Amprobe AM160 = Brymen BM859CFa), but I still use the UT61E in places where I don't really need the Brymen (to help prolong the life of the more expensive meters).

Gauss163 said:

I too have more accurate and precise handheld DMMs (e.g. 500000 count Amprobe AM160 = Brymen BM859CFa), but I still use the UT61E in places where I don't really need the Brymen (to help prolong the life of the more expensive meters).

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why would not using a meter prolong it's life such that it'd be noticeable? any decent dmm will work well for decades. bench meters will even last decades while being permanently powered on with some maintenance along the way.

for hand meters, I normally use a fluke 87v because the rotary switch is truly the most ergonomic one on any meter I've ever seen. I also have a brymen bm869 but the switch has far too much resistance for easy one-handed use while the meter is on its stand. obviously, if I wanted to do long term measurements or higher resolution/accuracy, I'd use a bench meter.

the problem with cheap meters is exactly their repeatability, consistency and linearity.

John, I also received the same AD584LH voltage reference from MS Huang in Guangdong. The data sheet included with my unit is IDENTICAL to your unit in every detail. I find this extremely unlikely. The documentation appears to be inaccurate. I ordered a PentaRef with outputs of 2, 4, 6, 8, and 10 volts from http://www.voltagestandard.com that should be delivered tomorrow. The PentaRef is much more accurate but costs a lot more. I also have one of the plastic housed AD584KH units. It is very convenient to use and appears to have accurate data.

TinderBox (UK) said:

It did come with this bit of paper, Great idea in the link about using 5x CR2032 =15V to power the reference.

The main IC on the board is "AD584LH1015"

John.

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When it comes to Made in China, Nothing amazes me anymore.

John.

A lot of the TO-99 package AD584 I see on eBay look counterfeit. Non-crisp ink, more rounded on top, maybe taller can too. Wouldn't surprise me if those aren't factory calibrated ICs at all, meaning your meter could actually be more accurate than it is.

John, since my last post on this subject, I bought an Agilent 34401a 6 1/2 digit DMM. My unit appears to be accurate to within 5 PPM. I have carefully measured the AD584LH reference that is like yours with an identical data sheet. At turn on the unit measured 2.49857, 5.00134, 7.49997, and 10.00226 VDC. After allowing it to stabilize for about 30 minutes it measured 2.49857, 5.00129, 7.49990, and 10.00218 VDC. I powered the unit from a 12 VDC, low noise regulated supply.

I also have two AD584KH units in plastic cases. One was advertised as an AD584LH unit, but it had a KH device, not a LH. The earlier AD584KH was bought from Amazon Prime and appears to be the most accurate. All listed readings were confirmed exactly on ALL 6 1/2 digits using my Agilent 34401a.. The units in the plastic case are much nicer and more convenient to use than the simpler and cheaper unit. The better plastic cased unit stated it was calibrated using an Agilent 3458, but only 6 1/2 digits were reported. You might consider buying one of the plastic cased units. The are available from ebay for about $15.00.

Thanks for the great information, on the subject of the case, can you post me an example ebay item number or pm me it so i know what i am looking for.

As long as my dmm meters are reasonable accurate it`s good enough for me, it`s only for home use.

Thanks

John.

John, here is a link to one of the easy to use units.

http://www.ebay.com/itm/KKMOON-High...831871?hash=item2ee2d0d2bf:g:caoAAOSw-vlVg5aZ

You need a 5 volt supply with a 5.5/2.1mm plug to charge the battery. Don't exceed 5.5 volts.

Google for AD584KH voltage reference and you will see lots of similar units. Ask the seller for what meter they use for calibration readings. There are many sellers and they don't specify details. Analog Devices quit making the LH version some time ago.

TinderBox (UK) said:

Thanks for the great information, on the subject of the case, can you post me an example ebay item number or pm me it so i know what i am looking for.

Click to expand...

Thanks i will add one to my future purchases

John.

billcushman said:

John, here is a link to one of the easy to use units.

http://www.ebay.com/itm/KKMOON-High...831871?hash=item2ee2d0d2bf:g:caoAAOSw-vlVg5aZ

You need a 5 volt supply with a 5.5/2.1mm plug to charge the battery. Don't exceed 5.5 volts.

Google for AD584KH voltage reference and you will see lots of similar units. Ask the seller for what meter they use for calibration readings. There are many sellers and they don't specify details. Analog Devices quit making the LH version some time ago.

Click to expand...

John, watch this video starting at 16 minutes in. It shows the easy to use unit in operation.

https://www.youtube.com/watch?v=zm_ZBT4t4dA

billcushman said:

The earlier AD584KH was bought from Amazon Prime and appears to be the most accurate. All listed readings were confirmed exactly on ALL 6 1/2 digits using my Agilent 34401a.

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That's the first I've heard of the cal data exactly matching. Everyone else has reported some discrepencies, which is to be expected since usually the cal data on the back was recorded much earlier, so there will be nontrivial drift. For example in the video you cited the cal cert lists 9.99993 but he measures 9.99954/5 on his Keithley 2000, a difference of 0.385mV.

It seems that either you got extremely lucky, or maybe there are new batches with more recent calibrations. What is the cal date on your label, and what is the date code on your AD584LH? If there are indeed some more recently calibrated units then it would be useful to know where to find them, since most seem to be at least a year old (but some list only the year of calibration).

The most accurate plastic cased AD584 unit was advertised as KKMOON High Precision, fulfilled by Amazon. It was like the link in the message to John. The cal dates on both the AD584 units was 2015. Both units have AD584KH devices (not sure if they are genuine). I also checked using a Doug Malone Voltage Standard PentaRef that I just received. What I was extremely lucky on was the Agilent 34401a. Its spec is 15 PPM for one day and 35 PPM for one year. My unit is 15 years old and appears to have the original factory calibration. It passes all self tests and has no reported errors. It had been certified several time but apparently never re-calibrated. I have never observed any error greater than 10 PPM even at turn on. With 15 minutes of warmup the error is usually less than 4 PPM.

Gauss163 said:

That's the first I've heard of the cal data exactly matching. Everyone else has reported some discrepencies, which is to be expected since usually the cal data on the back was recorded much earlier, so there will be nontrivial drift. For example in the video you cited the cal cert lists 9.99993 but he measures 9.99954/5 on his Keithley 2000, a difference of 0.385mV.

It seems that either you got extremely lucky, or maybe there are new batches with more recent calibrations. What is the cal date on your label, and what is the date code on your AD584LH? If there are indeed some more recently calibrated units then it would be useful to know where to find them, since most seem to be at least a year old (but some list only the year of calibration).

Click to expand...

billcushman said:

What I was extremely lucky on was the Agilent 34401a. Its spec is 15 PPM for one day and 35 PPM for one year. My unit is 15 years old and appears to have the original factory calibration.

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That's not extremely lucky - that's par for the course for high-end bench DMM's. It's not unusual to hear of 30 year-old HP DMMs that are still in-spec (or very close). How did you verify that yours is in spec?

Rather. what seems extremely lucky is that your AD584 still matches your cal certificate even though it may be over a year old. I've followed closely many of the threads on AD584 based references and never heard of anything like that before. The odds of that seem astronomical. To be sure I understand what you wrote, you are saying that that your readings on your 34401 exactly match those on your AD584 cal cert to all 5 places after the decimal point, for all 4 reference values? That's hard to believe since it exceeds even the short term drift reported (let alone long term drift), e.g. HKJ measured about 0.03mV variation over a couple hours.