[volt-nuts] What really gets calibrated?

[Fred Schneider]

It is not about cost but about building a history. If you send in a meter and they adjust it, send it back you will not know how much it is off. And also not if some projects, adjustments you made before that are done right. Also you do not know the amount of drift. It could be 10% off or only 0.1 ppm. 
But if you get it back and know 10V is 10,000.005 V and after the next session it is 10,000,004 and a year later 10,000.003 you can predict better what it will be half way in between. And you know it is very stable. But if you get it back every year at 10,000.000V and it was 10,000.010 the first year, 9,999.993 the next time and 10,000.040 the last time and do not get those values you think you have a very good meter but no history and no confidence. 

And if they adjust it, will the deviation be caused by something like mechanical stress on the trimpot or is the reference changing ? 

And if they calibrate and adjust it at 25 degrees , 1000 mbar and 70 % humidity. What will it be at 22 degrees, 1200 mbar and  50 % rH.

And that is the things of Voltnutting that can drivecypu nuts ;-) 

Fred PA4TIM

Op 29 jul. 2013 om 00:15 heeft Joseph Gray <jgray at zianet.com> het volgende geschreven:

> I recently had it explained to me that "calibration" is really just
> checking a piece of gear against a known standard, to see if it meets the
> manufacturers specification. If it is outside specified values, then it
> gets "adjusted", not "calibrated".
> 
> I can see that on the part of the calibration lab, it is easier and faster
> to simply check that a device meets spec and not have to spend time
> adjusting anything. It should also be less expensive for the customer.
> 
> My question is, is just meeting spec good enough? If an instrument is
> capable of exceeding spec, shouldn't it be adjusted to the best standard
> available? In other words, if spec says 2 ppm, but it can be adjusted to 1
> ppm, wouldn't you want to do that?
> 
> Joe Gray
> W5JG
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