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#142100 - 12/09/04 09:23 AM Test instrument accuracy
lyledunn Offline
Member
Registered: 06/30/02
Posts: 159
Loc: N.Ireland
Some electrical installation instrument manufacturers claim compliance with standards such as the BSEN 61557 However, I have noted that the standard requires an operating error of not more than 30%! Hardly worth doing the tests! Any views?
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lyle dunn
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#142101 - 12/09/04 02:40 PM Re: Test instrument accuracy
pauluk Offline
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Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
I think I've seen references to this standard which specify a maximum tolerance of 5%.

Maybe there are different levels of BS EN 61557 ?
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#142102 - 12/11/04 06:06 PM Re: Test instrument accuracy
uksparky Offline
Member
Registered: 07/06/04
Posts: 200
Loc: UK
Yes, there are different tolerances Paul. I can't remember them, but I'll try and find the relevant doc. It depends what is being measured, and under what circumstances.

I get my 16th ed meter and other test gear calibrated annually so I don't worry about the tolerance; it's all dealt with by the engineers.

[This message has been edited by uksparky (edited 12-11-2004).]
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#142103 - 12/12/04 03:45 AM Re: Test instrument accuracy
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Hi Guys!,
As far as I'm aware, there is more than one Standard around for test instrument Calibration.
The majority of our test gear used by the Power Board here, is referenced to VDE Calibration standards.
But I'm not about to play the European card here.
John,
Quote:
I get my 16th ed meter and other test gear calibrated annually so I don't worry about the tolerance; it's all dealt with by the engineers

I can see how that would work, I do the same thing here, we have a VDE licenced lab in Wellington and I can send the gear up there on Monday and have it back by Wednesday morning.
Efficiency Plus!!.
Getting back to what Lyle said in the first place, 30% is a little hard to swallow though, considering that we have to have a stated accuracy of 0.5-1% accuracy with most of our test gear here.
30% with a Megger could give you some really wayward results!.
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#142104 - 12/12/04 04:51 AM Re: Test instrument accuracy
lyledunn Offline
Member
Registered: 06/30/02
Posts: 159
Loc: N.Ireland
Trumpy,
The figures you quote are basic instrument accuracy under ideal conditions and not operating accuracy as may be the case in the field.
It matters little to the opeating accuracy if the testers are calibrated!
Like you Trumpy, I was a bit bewildered when I was informed about the potential inaccuracy of my first class Megger instruments. I guess some testing, regardless of the accuracy is better than no testing. Perhaps it would be better to state a result say an earth loop reading of 0.1 + or - 30%. (Gives a fault current between 1846A and 3400A based on 240v). So much for predicting a disconnection time!!!

[This message has been edited by lyledunn (edited 12-12-2004).]
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lyle dunn
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#142105 - 12/12/04 12:21 PM Re: Test instrument accuracy
uksparky Offline
Member
Registered: 07/06/04
Posts: 200
Loc: UK
Quote:
It matters little to the opeating accuracy if the testers are calibrated!


Not entirely sure where the logic lies in that...

Much of the tolerance in terms of operation is with connections; it is less likely that you will have a connection of 100% fastness in the field than in the test lab.
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#142106 - 12/12/04 05:23 PM Re: Test instrument accuracy
aland Offline
Member
Registered: 05/20/04
Posts: 186
Loc: United Kingdom
One thing we need to be mindfull of is that we test for poor connections not good! As you say UK great difficulty can be experienced in the field getting an ideal contact. Its most important to have some idea of what readigs you expect from the test you are doing. So many folks just accept anything that the meter says every time without question. As Lyle states in his example the variation can be terific. But by being alert when testing you can usually spot the poor result from bad contact.I carry a couple of resistors in my meter bag just to verify the overal accuracy of my meter if I get a reading I dont believe I check against the known resistor and test again. On a couple of occasions have had leads fracture at the probes causing very odd readings.
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#142107 - 12/13/04 02:30 PM Re: Test instrument accuracy
lyledunn Offline
Member
Registered: 06/30/02
Posts: 159
Loc: N.Ireland
Uk sparky,
Your right, there is no real logic in that statement. What I really meant was that even with a spot on instrument, operating error can still be as much as 30%, and this is considered acceptable by the BSEN standard.
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lyle dunn
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#142108 - 12/13/04 03:26 PM Re: Test instrument accuracy
uksparky Offline
Member
Registered: 07/06/04
Posts: 200
Loc: UK
Yep - I see where you're coming from!

"Odd" readings are a nightmare scenario for the person who isn't really sure what they're testing and, as Aland says, just accepts what the meter says without question. Now that part P is looming, I suspect that many a 'good' sparky will be testing away merrily without 100% knowledge of what they're doing. It's surprising what getting the "competent Person" status doesn't entail if the assessor is not too concientious!

The multi-funtion 16th Ed. testers are a bluddy minefield until you have mastered the damn things! I changed mine about two months ago and threw the handbook into the back of the van after about 20 seconds; it was a translation from Czech!! To be honest they are mostly far too clever for themselves...
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#142109 - 12/13/04 04:23 PM Re: Test instrument accuracy
aland Offline
Member
Registered: 05/20/04
Posts: 186
Loc: United Kingdom
What tester are you using UK? I have one of the New Megger Multifunction testers found it quite good. Does not save results to memory or anything like that. I do have a Chauvin Arnoux Multi Function tester that has that facility but I do not use it. Prefer to write results down on paper.
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