General > General Technical Chat
How do you calibrate your gear.
chinoy:
So I had a Fluke 105B where the buttons stopped working. And my kitchen foil hack also stopped working.
So I got a Hantek 5000 series Scope. The measurements did not match my old fluke scope. So I got a new Fluke 223A.
Now every measurement I take is different. The new fluke does not match the old fluke. And the scope matches nothing.
I know there are labs where you can send in your gear to calibrated.
Also know that the new Fluke 223A can be re-calibrated.
My interest lies in measuring very low voltages only i.e. all under 1 Volt.
You know the kind of voltages you get off a tape head.
Are there any tricks or easy ways to confirm my meters accuracy ?.
Like maybe buying a new battery or building some kind of circuit that puts out a very accurate voltage I can use to calibrate my gear.
tggzzz:
More information needed....
Numbers, not adjectives.
Define measurement techniques.
Compare results with specifications.
Pictures showing "incorrect" results.
Psi:
You can't compare a scope voltage measurement to a DMM measurement.
A DMM is designed to accurately measure voltage.
A scope is not, in fact many scopes only have 8bits of vertical resolution, although 10bit is getting common.
So if your scopes vertical scale is set to say 1V/div and your scope's screen has 8 divisions, and the trace is in the middle, then you can measure +/- 4V.
The 8bit vertical resolution means your +/- 4V is represented by a number between 0 and 255, and that is not much at all
chinoy:
The new Fluke DMM says 6000 count. Could you explain that in simple english.
I really dont understand why pictures. Im measuring a point on the PCB. I need to turn a trim pot till I get 0.45 volts
If every meter is giving me a different reading Im not sure which one to trust.
A friend told me just go with the new Fluke as they would have done some kind of calibration before shipping it and its the newest of all the gear you have.
I have some other 6000 count no name meters but even here every reading is different.
On the scope I press the measure button and it throws up RMS voltage which is what I'm taking as the value. And confirming it with the scale Im running at i.e. 100 Mv per division. Even if I could just figure out of the meters is the most accurate Id be happy.
There must be some circuit or trick to get an accurate number. I even tried 3.3 Voltage regulators but even voltage regulators have a margin of error. i.e. the out put changes from IC to IC.
alm:
First, realize that to calibrate means to get a piece of paper (or PDF file) that says whether the unit was within set specifications. Be sure to actually specify if you want adjustments.
Every decent test instrument will come with specifications like the displayed value should be within 0.9%+0.5%, which means 0.9% of the reading (e.g 1.5V) and 0.5% of range (e.g. 6V). Or 0.9%+5 digits, which is 0.9% of the reading + 5 least significant digits.
If you measure the same signal with two meters in parallel, and both meters are within their specifications, then the intervals of the minimum and maximum actual values calculated from their displayed reading plus and minus the uncertainty calculated from the accuracy specifications should overlap. The actual value should be in the overlapping range.
Be sure to pay attention to little footnotes like "only valid after zeroing", "only valid from 5%-100% of full scale", "only valid for sinusoidal signals from 40 Hz to 500 Hz" etc.
If after this exercise the meters are not overlapping, then one or more will need adjustment. If they are overlapping, then you might be expecting too much. A brand new Fluke meter should be well within its specifications, so I'd trust that (within its specified accuracy).
Check the manual for adjustment procedure. While there are some affordable standards like the DMM check plus that can be used as a sanity check, adjusting a DMM generally requires a range of signals from 100 mV to 1000 V DC and AC, etc. Some instruments allow you to just adjust a single range, other require going through all ranges and functions before they will save the adjustments.
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