I bought a Fluke T5-600 volt/amp meter recently and the accompanying literature says it was calibrated at the factory and could be sent in to be calibrated annually.
I can understand how analog meters with moving parts might lose accuracy, but why would a digital device need to be re-calibrated?
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I am trying to think, but all voltmeters and I think all phyical measures are the comparision of some parameter to a reference, either directly (in the device) or by indirect reference (the reference in the deviced compared to some master reference).
And if that reference changed or if the method of doing the comparison was faulty then you will get the wrong measurement.
In the case of an analog volt meter it is comparing the magnetic force from a current in the a coil to the force of a spring. And resistors are used to convert the voltage to current.
In the case of a digital voltmeter is reference is a fixed voltage produced by a semiconductor. There are a number of different ways that the measurement can be make. One methode is connect the unknown voltage to capacitor for a fixed period of time. Then discharge the capacitor using the reference and measuring the amount of time that it takes to get back to zero. Now that system change in the timming or the capactor will be balanced out. But changes in the reference or voltage divider that is ued to reduce the unknow down to a low level can change. Also if capacitor because leaky then it would affect the accuracy.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
why would a digital device need to be re-calibrated
Usuallly because if a meter is used in an application for testing other equipment a specification may require re-calibration on an annual or semi-annualy basis.
For general work, you will not need to recalibrate the meter in your lifetime.
Good digital meters use bandgap references (stable over time and temp) and laser trimmed metal film resistors (vs. adjustable pots). Cheaper meters (like the $3 HF meters) have pots adjusted at the factor which may drift over time, but not so much you would notice in construction work.
I've not taken a T5 apart like I have many other types of Fluke and others, but Unless you are doing a test to a military contract spec, dont worry about ever neededing to recal your meter.
Ditto. Calibration is unnecessary unless you're doing work that requires certified instruments.
If your view never changes you're following the wrong leader
Thanks guys.BruceT
in case it losses accuracy ;)
"It is like hitting yourself in the head with a hammer: it feels so good when you stop"
If you don't know why it needs to be calibrated, then it doesn't need to calibrated.
Disclaimer:
The above is a true statement, and was meant to be humorous, not insulting.