Tony Albus  Stability Siglent SDM3065X Gw-Instek GDM9061 Keithley DMM6500 34401A - Page 1
Forum section: electronics / general

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 05, 2025, 02:01:30 pm
content: I just watched the Tony Albus DMM stability test.... and I don't really agree with his conclusions.The table at @08:44 shows that 4 of his 5 meters are "drifting upward" by around 20 or 30 uV, and th 5th (Siglent) is known to drift a lot during startup anyway. From that I conclude that it's more likely that instead, his reference is drifting. His reference is an (@03:06) DMM Check + which uses an: LT1021BCN8-5.The bottom half of the numbers of the table @08:44 look like a big red herring to me. All meters except the Siglent are so close together that they are all just "the same" for as far as this stability test is concerned.The Siglent (EUR820) is clearly falling behind in stability compared with all the others. (TheDefpom agrees in the youtube comment the Siglent stabilizes after 4 hours). I also find it remarkable that the Gw-Instek (EUR1070) is within a few counts of the Keithley (EUR 2200). CMM6500 would be a bit much for many people, and if price difference between the Gw-Instek and Siglent is an issue, then the Gw-Instek GDM9060. (Slightly reduced spec compared to the the 9061but same price as the Siglent) seems to be a better option.The Gw-Instek also has two voltage references: LM399 and MAX6325,@25:31 Is this for some self-calibration feature?Apparently Gw-Instek has a quite good reputation. It's a bit of a shame there are so few decent reviews of Gw-Instek stuff on Youtube.https://dmmcheckplus.com/technical-informationEdit: Fixed two dumb mistakes, both noticed by tatel (below).Reference is of course drifting in the same direction as the assumed drift of the 4DMM's, andthe duration was 4 hours instead of two.

author: iMo
author_rank: Super Contributor
timestamp: August 05, 2025, 04:23:51 pm
content: Quote from: Doctorandus_P on August 05, 2025, 02:01:30 pmAfter I posted link to his ADR1001 video I would expect he will be using it for his next testing with those meters..

author: tatel
author_rank: Frequent Contributor
timestamp: August 05, 2025, 04:43:23 pm
content: Quote from: Doctorandus_P on August 05, 2025, 02:01:30 pmNot that I want to get into any arguments, but I would really know more about your reasoning. To me, if four out of five devices mostly agree, and the fifth is the only outlier, I would be pretty much confident that 5th device is effectively an outlier. Particularly if it "is known to drift a lot during startup"Also I'm not very sure about the reference drifting downwards when four of the devices are drifting upwards. I would think the reference is perhaps drifting upwards in that case. Could someone explain that to an ignoramus like me?QuoteWell, 4 hours, which is what I see in that comment, is after 2 hours, no doubt about it. To me, it means one can't be that much confident the Siglent is giving a good reading until 4 hours from start. Therefore the other four, similar readings, are probably more trustworthy?QuoteI agree on that. So that GW-Instek would be a sensible purchase for a hobbyist looking for a brand new DMM. I can also see the best bang for the buck would be a second hand 34401. Quite pleasant to see them performing so well.

author: 2N3055
author_rank: Super Contributor
timestamp: August 05, 2025, 07:21:46 pm
content: Stability and warmup time are not the same.And also (quote):"The 34401A usually needs about 2h to fully stabilize - but you need constant room temperature to achieve ~ppm stability." - Dr. FrankThe very fact that every single of those meters has different position, thermal environment and airflow makes any comparisons just anecdotal tales. Even difference in cables and routing can be seen at ppm levels.