Products > Test Equipment
Decent benchtop multimeter for beginner?
skander36:
--- Quote from: KungFuJosh on August 17, 2024, 11:09:16 pm ---...
If you feel like doing the same test as me, I would love to see that info. 1 hour warmup, 4 hours tracked, then reset data and continue tracking for 4 hours. I want to see how your PP compares. 🤣🤣🤣🤣🤣
--- End quote ---
This doesn't make any sense to me. My point was a compare between three different DMM's.
G0HZU:
--- Quote from: Phil1977 on August 15, 2024, 07:08:20 am ---Maybe a blasphemy question, but what do you need 6-digit absolute accuracy for - except for calibrating other instruments?
All validation/qualification labs I know had basic requirements of 0.1% or in rare cases 0.05%. If your meter should be one order of magnitude better than your specification you get to 0.005% - these are 4 1/2 digits.
Of course you can use 7 or more digits for relative purposes. Seeing small changes also over a large timespan is a great feature, so the instrument should have sufficient stability. From a pragmatic point of view this stability can also be ensured by tracking an external standard instead of going through the exhaustive and expensive complete calibration process.
What are real life applications for 6 digit absolute accuracy and not only stability? I´m curious.
--- End quote ---
Few professional people will need the absolute accuracy, but because DVM technology has been 'boringly brilliant' for several decades now, the internal reference accuracy and stability justifies 6.5 digits or maybe more for a decent bench multimeter.
In my experience, 6.5 digit meters generally offer other features making them very attractive for professional ATE systems. They offer fast read rates and various inbuilt math functions and they offer GPIB and/or USB and/or LAN interfaces.
In all my years at work, I have never seen any engineer get excited when a decent DMM was returned from calibration. Also, I don't think I've ever seen an engineer check two 6.5 digit DMMs against each other in the way many hobbyists do obsessively. Many of them seem to progress to obsessing over state of the art voltage references and calibrators.
Don't ask me what they think they need this stuff for, but in other hobbies there will always be people who want either the titanium/platinum/silver/gold version of whatever widget(s) the hobby demands. I think it's partly a status thing, partly a FOMO thing and partly an OCD thing.
KungFuJosh:
--- Quote from: skander36 on August 17, 2024, 11:30:51 pm ---
--- Quote from: KungFuJosh on August 17, 2024, 11:09:16 pm ---...
If you feel like doing the same test as me, I would love to see that info. 1 hour warmup, 4 hours tracked, then reset data and continue tracking for 4 hours. I want to see how your PP compares. 🤣🤣🤣🤣🤣
--- End quote ---
This doesn't make any sense to me. My point was a compare between three different DMM's.
--- End quote ---
You compared the 3 devices from cold start. I'm curious about the actual stability of your DMM, which requires warmup time first. You could still measure all 3 if you want to compare.
Comparing between 3 DMMs is fun, but if you want to see if there's an actual problem with one of them, you have to test it properly.
I just saw this post:
--- Quote from: skander36 on August 17, 2024, 05:18:35 pm ---Josh, you write a lot of personal assumptions (AKA BS).
The point is not he performance but a comparison between them.
The meters was tested in the same time. As KS and KT was able to keep a reasonable reading, so Siglent should stay aside. If not in my opinion is inferior. You may have your personal opinion of course.
-No, none of the meters doesn't show the actual value of the reference, they can't as they are 6.5 digit and this value is from a 3458A used for calibration. Actually the real value is 10.000001 after adjustement. 10.000005 was before (after 1 year and 8 month from fabrication) see picture from adjustement.
The drift will eventually stop after 3 about hours - see attached.
--- End quote ---
That's what I correctly assumed, an 8.5 digit meter. That number also has to take into account temperature and humidity. Did you when you tested your 3 meters? You will never match that number otherwise.
Your results are BS if you wanted to test or compare anything besides cold start drift. It's simply not accurate to claim you have a problem based on cold start. That's not an opinion or an assumption. Every device requires warmup time to meet specs.
I'm not saying the Siglent isn't inferior to the other two meters. I would love to have a DMM6500 if I could afford it. That doesn't make my Siglent a piece of crap; it's just not as nice as the meter that costs twice as much. I'm not shocked by that.
bdunham7:
--- Quote from: KungFuJosh on August 17, 2024, 11:02:13 pm ---Wasn't that 27ppm noise?
--- End quote ---
No, that would be terrible. 27µV is what is displayed in the box, that's 2.7ppm.
--- Quote ---I didn't test cold power up at all since it's sort of pointless. Ignoring warmup times for both the ref and the meter doesn't make any sense to me.
--- End quote ---
First, characterizing your meter so you know how it behaves can be helpful because then you'll know how long you have to let it warm up before you can get a certain level of accuracy. Second, the power-on settling data can give you some idea of what the TC of the unit will be like. An hour is an arbitrary time, regardless of whether or not it appears in a manual. You might discover that for all practical purposes your meter is spot-on after 5 minutes or you might find that it is not even well within spec until an hour goes by. Either result may be technically acceptable and no cause for complaint, but it is still useful to know.
KungFuJosh:
I suppose I should be less lazy. I might have been using an online calculator that said 0.000027 = 27ppm. Ok, 27uV is 2.7ppm. Cool. I assume there's some context as to why there's a discrepancy.
Fair enough. I often use my DMM with 1 minute of warmup, I haven't had any issues. I also don't usually test anything that cares about uV resolution.
Tomorrow I'll test both from cold start. Or should I warm up the ref first, to separate that? It makes sense to me to warm up the ref first remove the ref's drift from the test.
ETA: removing the ref's drift might prove difficult if I can't keep my room consistent as my other test showed (even if it was obvious).
Thanks,
Josh
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