### Author Topic: Is accuracy even that important?  (Read 1395 times)

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#### FriedMule

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##### Is accuracy even that important?
« on: June 12, 2021, 10:37:47 am »
Short story:
I have a couple of handheld DMM's and a couple of cheap hung low bench DMM's plus my "flagship" bench DMM, all showing different values in the micro voltages.
My power supplies does also show their values, who does not match any of my DMM's.
I am speculating on calibrating power supplies and hung low DMM's so they agree with my "flagship" DMM.

Question:
If I chose to calibrate my gear to agree with my flagship and my flagship may be a couple of micro voltage off, does that even matter?
If my gear is agreeing on the voltage, then should I get a fairly precise relative reading. I.e. 5V in is what my gear shows is 5V in and if I get 3.25V out do I know it's a fairly precise change of 1.75V in relation to input, ignoring it could be 5.013V in if measured by perfect gear and 3.263V out.
Even if I appear online is it not necessary so, my computer is on 24/7 even if I am not on.

#### Brumby

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##### Re: Is accuracy even that important?
« Reply #1 on: June 12, 2021, 10:44:08 am »
Question:
If I chose to calibrate my gear to agree with my flagship and my flagship may be a couple of micro voltage off, does that even matter?

Horses for courses.  It completely depends on what you are measuring.

If you are working with typical Arduino level circuits, then a cheap 31/2 digit meter is more than adequate.

If you are working with 24bit ADC or metrology circuits, then you'll need something a bit more high end.

#### Fungus

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##### Re: Is accuracy even that important?
« Reply #2 on: June 12, 2021, 10:55:27 am »
The only important thing is to know your meters.

We all like having a lot of digits but let's face it: 1% accuracy is plenty for most work.

More digits are useful for measuring differences, eg. I just measured the voltage at the start and end of some 30AWG wires to see what the voltage loss was along them.

(0.13V if you must know...  )

Question:
If I chose to calibrate my gear to agree with my flagship and my flagship may be a couple of micro voltage off, does that even matter?

No.

a) It might matter psychologically but it won't make your circuits any better.

b) Messing with gear to adjust it isn't risk-free. You might make it worse.

c) Most of these things will vary with temperature. Trying to get non-temperature compensated gear to agree down to the last digit is a fools errand.

#### Pfriemler

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##### Re: Is accuracy even that important?
« Reply #3 on: June 12, 2021, 10:56:40 am »
I know this :-)
I bought a cheap voltage standard, had my son at work compare it to a high precision meter (it was accurate) and made an accurate 10V out of all the readings between 9.94 and 10.1 volts as far as it went, just for peace of mind. Only one can not be calibrated so easily and shows 9.96V. That is less than 0.5% deviation. Related to a power supply, the influence of the output cables is already bigger.
As said, a good multimeter for the few important accurate data is enough. The rest is only for the optics.
« Last Edit: June 12, 2021, 10:59:14 am by Pfriemler »
once you do it right, it works :-)

#### Brumby

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##### Re: Is accuracy even that important?
« Reply #4 on: June 12, 2021, 10:59:12 am »
Separate to the topic of accuracy is resolution - yes, these are two different things!!!

This is where you have the ability to detect changes at the Least Significant Digits level.  The actual number displayed may not be completely correct, but if the numbers are going down, then you can be reasonably sure the value you are measuring is going down - and the magnitude of that change is reasonably correct.

There are times that this sort of measurement is quite useful - such as seeing the voltage sag on a power rail when a load is connected.  Whether that power rail measures as 12.01V or 12.03V isn't necessarily as important as seeing it drop by 0.5V - especially when, for example, it's supposed to be a regulated supply.

#### Kleinstein

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##### Re: Is accuracy even that important?
« Reply #5 on: June 12, 2021, 11:19:11 am »
For many uses the accuracy of a voltmeter is not very important. More often it is about detecting small changes or just measuring votlage that are overall small (e.g. thermocouple).  Especially a scale factor that is slightly off can often be tolerated, though it can get complicated when comparing readings from different meter (e.g. 2 meters measuring the voltage on different side of a cable).

With lower grade DMM there is little to be done on calibration and an adjustment may not be possible.  Quite often an official calibration (like needed for some professional uses) is testing only, telling you the meter is still well within specs. An adjustment is usually not done unless the DUT is way off - in this case a cheap meter is usually marked as defect and disposed, as it would not be reliable even after an adjustment. In some areas it can be cheaper to by new instead of a calibration.

With a good, reliable meter and some suitebale sources, one could do the testing of the lower grade meters (more than a factor of 10 lower specs). So there is very limited use in sending some of the lower grade meters to calibration.

#### J-R

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##### Re: Is accuracy even that important?
« Reply #6 on: June 12, 2021, 11:52:02 am »
If you're just checking batteries and wall sockets around the house, accuracy may not matter.  1.5V battery OK, 1V not OK, 12V battery OK, 11V, not OK.  0V-120V-240V 50/60Hz...  Just the basics.

But I say if you have an interest in electronics, understanding the concepts and aspects of obtaining accurate measurements is a worthy exercise.  However, without a recent calibration certificate or a reference standard, making things agree is pointless.

Smf