Visualizing multimeter voltage measurement error - Page 1
Forum section: electronics / testgear

author: graybeard
author_rank: Frequent Contributor
timestamp: March 20, 2025, 06:31:03 pm
content: I will be giving a lecture in a few weeks on using various types of test equipment. The audience is senior and 1st year graduate EE students.I want to show the specified maximum measurement error vs. reading for a few different multimeters in DC voltage mode. Just looking at the meter specifications does not give a good feeling for the numbers. These made these graphs are to help them visualize better visualize the numbers.Although the Bryman meter has a 500,000 count mode, the specifications do not claim any more absolute accuracy.I welcome any comments.Thank you,Chris

author: Kleinstein
author_rank: Super Contributor
timestamp: March 20, 2025, 08:49:55 pm
content: It is a nice visulization.The Hp34401 curves still have a small mistake: the ranges only have an overrange to 12 V, 1.2 V and so on. It is also not so clear how the specs apply to the overrange part.

author: bdunham7
author_rank: Super Contributor
timestamp: March 20, 2025, 09:05:00 pm
content: As mentioned, the 34401A is 1.2M counts. I'm not sure I'd use the 24h/Tcal+/-1C specs if you are doing comparisons.The graphs were not immediately intuitive to me, but I did finally grasp what you are doing. Students who have hopefully already been exposed to measurment uncertainties may not grasp it immediately either. It's an interesting idea.I'd suggest that if you are comparing meters this way, you use identical horizontal and probably vertical scales for all charts and not expand them to fit the ranges and resolutions of each meter. This will give an easy visual comparison of both error and measurement capability.

author: tautech
author_rank: Super Contributor
timestamp: March 20, 2025, 09:13:53 pm
content: Chris shared privately one he presented on DSO's....good stuff !

author: RoGeorge
author_rank: Super Contributor
timestamp: March 21, 2025, 09:25:31 am
content: My Metrix mtx3283 handheld DMM can show the worst possible min/max range for whatever measurement is on the display. Has a dedicated 'spec' button to show that.

author: 2N3055
author_rank: Super Contributor
timestamp: March 21, 2025, 09:40:56 am
content: Quote from: RoGeorge on March 21, 2025, 09:25:31 amHehehe you were faster...Yes, Metrix graphing meters have that mode.They also display what is current input impedance..They have some nice different thinking in design.@graybeard, i like that you are trying to find ways to illustrate this. I would agree with bdunham that it might be also interesting to plot on a absolute unified scale, so students also get an intuitive feeling what is domain of 3.5 handheld and what is a place of 8.5 digit meter, and everything in between.Also maybe shade an area where measurement setup starts to be an issue: what are voltage ranges, where we need to pay attention to controlled temperature, wiring, shielding....So they don't think it is trivial to measure 120µV DC to certain accuracy although some DMMs clearly seem like they should do the job.

author: graybeard
author_rank: Frequent Contributor
timestamp: March 21, 2025, 06:17:22 pm
content: Quote from: 2N3055 on March 21, 2025, 09:40:56 amSources of measurement errors including thermal voltages, rfi, magnetic coupling, capacitive coupling, leakage currents, ground loops, are already included on slides.

author: Aldo22
author_rank: Super Contributor
timestamp: March 21, 2025, 07:05:31 pm
content: Quote from: 2N3055 on March 21, 2025, 09:40:56 amWhy do you think it's not trivial?I just tried this with my cheap DMMs and I'm actually amazed at how the two match up.

author: 2N3055
author_rank: Super Contributor
timestamp: March 21, 2025, 08:22:18 pm
content: Quote from: Aldo22 on March 21, 2025, 07:05:31 pmWhat temperature, what repeatability? How much error is that?

author: graybeard
author_rank: Frequent Contributor
timestamp: March 21, 2025, 08:42:49 pm
content: Quote from: 2N3055 on March 21, 2025, 08:22:18 pmThat is on additional slides that include the use of control parts (golden standards).

author: graybeard
author_rank: Frequent Contributor
timestamp: March 21, 2025, 08:45:38 pm
content: Thank you for the comments and suggestions. I put all three of these slides on the same scale they are easy to compare.Thank you,Chris

author: 2N3055
author_rank: Super Contributor
timestamp: March 21, 2025, 08:59:46 pm
content: I think your audience will enjoy a very interesting and good presentation! Very nice.

author: Aldo22
author_rank: Super Contributor
timestamp: March 21, 2025, 09:29:53 pm
content: Quote from: 2N3055 on March 21, 2025, 08:22:18 pmAre these questions you would like to have answered, or are these questions I should ask myself?I'll answer them anyway:1. 22°C (The ZT-225 in the photo above shows the temperature above the measured value).2. Repeatable at the same temperature (I have not tested other temperatures). The last digit fluctuates by ±1.3. The specified DC accuracy is ±(0.05%+3)P.S. You are right, the measurement changed after I put the DMM in the fridge for a while.

author: bdunham7
author_rank: Super Contributor
timestamp: March 22, 2025, 12:21:22 am
content: The Aneng 8008 has a 10mV range with a floor of 3µV, equal to the 34401A and an order of magnitude better than the Brymen as well as >6X better than a Fluke 289 in its 50mV range? That's a very impressive claim. I'd suggest testing it with 10µV and 100µV stimuli.

author: TopQuark
author_rank: Frequent Contributor
timestamp: March 22, 2025, 06:45:51 am
content: Nice graphs! Measurement uncertainty is something I'm always aware of when making measurements, but rarely would I go the the effort of digging up the spec sheet to calculate the uncertainty band unless I'm making critical measurements. This makes it easier to visualize things.May I suggest using engineering notations with SI prefixes (10mV, 100mV , 1V ... ), instead of scientific notations (1E-2, 1E-1, 1E0 ...) for the axis labeling? It would be much easier to parse for engineers, and matches up better with what is displayed on the multimeter screen

author: Aldo22
author_rank: Super Contributor
timestamp: March 22, 2025, 08:42:30 am
content: Quote from: bdunham7 on March 22, 2025, 12:21:22 amIn any case, it is amazing how the cheap DMMs match up.Of course the last digit dances a bit and I'm sure the measurements will fluctuate with temperature changes etc, but for $15 to $30 they are quite usable for the hobbyist.Attached photos: 10µV, 20µV, 100µV.(Funny wiring, I know...)

author: Kleinstein
author_rank: Super Contributor
timestamp: March 22, 2025, 10:13:23 am
content: The accuracy specs are claims for the confidence levels of the manufacturers. They are nothing that can be directly measured and depending on the manufacturer there can be quite different factors from the typical observed deviations to the specs. Especially the Chinese instruments tend to have bold performance claims that are a bit suspect and turn or false. With the accuracy claims it is not easy to show, but confidence is usually lower than with high end brands like Fluke.A problem is that the specs are usually written when the meter is new, but real data on long term drift are usually only available a few years later. This is especially a problem for new products, that are not just modifications to an older design.So the comparison between brands is a bit tricky and one should take the claims with a pinch of salt.

author: Furna
author_rank: Frequent Contributor
timestamp: March 22, 2025, 02:24:57 pm
content: Quote from: graybeard on March 21, 2025, 08:45:38 pmI would add the basic accuracy (just on top of the image, next to "24hours ..") to the slide about Agilent 34410a.

author: bdunham7
author_rank: Super Contributor
timestamp: March 22, 2025, 09:17:18 pm
content: Quote from: Aldo22 on March 22, 2025, 08:42:30 amYour wiring is working as well as expensive low-EMF cables. Apparently thermal voltages aren't a thing in your corner of the universe? I guess Zotek has actually accomplished some pretty good zero control.

author: Aldo22
author_rank: Super Contributor
timestamp: March 23, 2025, 02:07:38 pm
content: Quote from: bdunham7 on March 22, 2025, 09:17:18 pmYes, I think that exists here too.Thank you for making me aware of it.I did a little experiment with a gold-plated test tip and a crocodile clip. Heated up with a hairdryer.In the pictures you can see cold (same temperature) and heated clip.176µV. Not bad!

author: Kleinstein
author_rank: Super Contributor
timestamp: March 23, 2025, 04:22:08 pm
content: Thermal EMF can be an issue. Here the handheld meters even have a slight advantage over the bench top ones: with low power consumption there is one a small heat source at the meter. Bench meters, can be quite warm causing a heat flow from the terminals. This can cause thermal EMF problems from not so good cables if the wires are not symmetric.