Test instrument accuracy

[lyledunn]

Some electrical installation instrument manufacturers claim compliance with standards such as the BSEN 61557 (British and European). However, I have noted that the standard requires an operating error of not more than 30%! Hardly worth doing the tests! Any views?

Regards,

Lyledunn

 

[buzzp]

Well, yeah thats a bit extreme. I would never buy a piece of test instrument with this kind of accuracy. Have never heard of this standard but if this is really a 30% accuracy then I would never even consider this a relevant standard unless there is something else in there that makes it important.

 

[Bung]

Not more than 30% where on the scale? Let's not condemn things on incomplete information - a percentage must have th base quoted before you can draw meaning form it. The base is not quoted here.


Bung
Life is non-linear...

 

[lyledunn]

This 30% figure is operating accuracy not basic instrument accuracy. So for example my earth tester has a basic instrument accuracy of +or- 2% +or- 2digits. Fine under ideal laboratory conditions but in the field the propensity to error is significantly increased. Thus the reading on my instrument might be 1ohm +or- 30%. Wow!!

Regards,

Lyledunn

 

[Skogsgurra]

Don't blame the instrument in cases like the ground resistance measurement. The ground resistance changes more than that over a few year's time. And you will get different readings from one measurement to the other. It just reflects the fact that not all properties are well defined or constant. It is a fact of life. Do not expect life to be perfect. Not even accurate - or constant...

 

[Bung]

... or precise.

Bung
Life is non-linear...

 

[buzzp]

What type of equipment is this for? Is it for ground resistance tests?
30% on a normal scale is unacceptable for traditional test instruments (not ground resistance, although it may be but I am not real familiar with these instruments). Is this 30% for very small readings? Do they give a range of accepting accuracies based on amplitudes of the measurements? If only 30% is mentioned it is worthless when it comes to an accuracy spec ('operating' or otherwise).

 

[lyledunn]

buzzp, they are earth loop impedance testers reading in ohms with a resolution of 0.01. An inaccuracy of such magnitude as 30% would result in significant difference in fault current assessed and thus on the disconnection time of fuses. The thing is that I really cant accept that this 30% figure is accepted as a maximum.

Regards,

Lyledunn