Products > Test Equipment
Brand new Bm869s calibration
radiolistener:
I don't have voltage standard, but I have ADR290E 2.048 V ± 2 mV reference.
And my BM867S measure it as 2.04828 V just out of the box.
Now, after 3 years it is measured as 2.04826 V.
I didn't performed calibration.
bdunham7:
--- Quote from: mrdave45 on February 19, 2021, 03:04:04 am ---I've been searching round the forum about the 869s and it seems there's quite a few comments about these being far off calibration out the box.
I've also read a few posts about people doing a quick calibration. I would have thought a fairly sophisticated pice of kit is needed to calibrate a meter properly beyond checking against a 5v source or whatever.
Do I need to get a calibrated one, to what level, or should I get one stock and put that money towards an ltz1000 reference.
Im mainly needing voltage and frequency to be super duper out of this thing.
--- End quote ---
I doubt that Brymen is shipping out-of-spec meters, but you shouldn't expect a 500K count meter to be exact to the last digit--it doesn't work that way. The few mentions I've seen of meters being 'off' is by people with unfounded expectations of some sort or another.
If you need a certain level of precision and accuracy, you need to look at the specs and mathematically understand what is called an 'uncertainty budget'. "Super duper" is not going to cut it. For any given measurement, you need to know how far off the actual value is likely to be. This is actually a statistical issue, but it is commonly boiled down to a single value and a confidence level. So you might conclude (these are just made up numbers) that your 5.00000 volt reading actually tells you that the true value is between 4.99930 and 5.00070 with a 95% certainty. If the confidence level isn't stated, you just have the specs and you can treat those as the limits, but you don't really know how certain you are. I think of it in terms of counts--how many counts represents the limits of the meters specified uncertainty. So when I look at a Fluke 8846A displaying 10.00000 volts, I know that the specified uncertainty is +/- 29 counts with a 99% confidence level, as long as I'm within the 1 year calibration period and between 18C and 28C ambient temperature.
A calibration certificate is just paper, so unless you need paperwork, I doubt it will get you a more accurate meter.
As for self-calibration, you can check and verify it yourself in a limited fashion with a DMMCheck or random 'standards' like that, but this really only tells you when and if your meter is broken. The actual calibration isn't difficult if you have the standards, but in most cases I think you would just make it worse. I definitely wouldn't go trying to tweak it so that it reads exactly 5.00000 volts just because it makes you happy--that is a fools errand that will simply leave you thinking you have something that you don't.
mrdave45:
That's brilliant, thanks all! That looks like its plenty good enough for what I need.
I think Ill just order one. Still need to get an lcr meter and a logic analyser. But i guess thats for another topic.
mrdave45:
I just wanted to be sure that I could get a meter that I could be reasonably sure that would be accurate to the mV and it looks like this will be without having to resort to the calibration cert.
joeqsmith:
Personally, I would hold off until you have a better understanding of what you actually need. You would be amazed how many people write that they bought the wrong product and then want to modify it. :palm:
--- Quote from: mrdave45 on February 19, 2021, 05:40:47 pm ---I just wanted to be sure that I could get a meter that I could be reasonably sure that would be accurate to the mV and it looks like this will be without having to resort to the calibration cert.
--- End quote ---
I too would like to have a meter that could read accurate to 1mV on a 1000V signal.
Something a little more realistic, my Fluke standard attached to three meters. Note the mV reads 0.2, 1.1 and 3.4. For me, this is good enough. For you, maybe not.
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