What tolerance is acceptable?

[Goody]

When testing your meter with "Resistance Check Box", if you get 1.99 instead of 2 ohms, you know the reading is within the range. But what exactly is the acceptable tolerance in these cases? Is it 99%? Thanks!

 

[tony mc]

I think GN3 covers the instrument accuracy.

 

[telectrix]

a small change in temperature will give you more variation than that. i wouldn't worry.

 

[tony mc]

Just checked mine.

Loop test +or - 5%

RCD trip + - 1ms

IR 1000V + - 2%
500 & 250 + - 1%

continuity ohms + - 1% + 20 m ohms

Thats on the instuctions of my kewtech fc 1000 fastcheck

Hope that makes sense.

 

[Goody]

Thanks for the replies folks. Cheers!

 

[MarkieSparkie]

GN3 says a basic accuracy of 5% (+- 2.5%) is usually adequate. Analogue instruments require a basic accuracy of 2% of full-scale-deflection in order to provide the required accuracy of measurement over a useful proportion of the scale.

 

[JUD]

GN3 says a basic accuracy of 5% (+- 2.5%) is usually adequate. Analogue instruments require a basic accuracy of 2% of full-scale-deflection in order to provide the required accuracy of measurement over a useful proportion of the scale.

That's actually ± 5% (95% - 105%).

Different checkboxes have different working tolerances. Mine is ± 5%.

The CalCard which is recommended by the Part P schemes is ± 3%.

 

[MarkieSparkie]

I beg to differ GN3 says 5%, that's the intrinsic uncertainty. +-2.5% of nominal.
BS EN 61557, however, gives intrinsic uncertainties of:- Volts 0.8%, R[SUB]LO [/SUB]1.5%, R[SUB]INS [/SUB]10%, Z[SUB]L [/SUB]6%, Delta T 1%, I Delta n 5% and R[SUB]E [/SUB]3.5%.
The actual values of resistors in any check box is irrelevant as long as they span the range of the instrument. It's not a calibrator or standard, merely a check method. The important part of the check box routine is the record of results, because you seek to identify a significant trend of variance from your initial results that allows you to question the instrument accuracy.