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Topic Title: Test Equipment Accuracy
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Created On: 01 June 2012 02:22 PM
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01 June 2012 02:22 PM
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Lorna

Posts: 2
Joined: 15 June 2009

Hello

I'm trying to understand the accuracy of a PAT tester which states the resolution, % and digit tolerances of individual test types.

My calculations are below for a hypothetical test and I would be very grateful if anyone could tell me if I'm doing right.


Resolution = 0.01 (2dp)
Accuracy = ±5% ±2 digits

Test Reading = 15.50

Step 1:
Determine the % tolerance
15.50 * 0.05 = 0.775

Step 2:
Round to 2dp = 0.78

Step 3:
Add the digit accuracy to least significant figure

= 0.78 + 0.02
=0.8

Therefore for a reading of 15.50

± 0.8 (5.16% of 15.50)

Upper limit = 16.30
Lower limit = 14.70

Thanks for your time :-)

Lorna
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13 May 2013 02:29 PM
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kengreen

Posts: 72
Joined: 15 April 2013

Lorna,

Afraid I don't understand the Jargon in your Post - a bit before my time - but there is a sad lack of learning in the matter of estimating errors. Are you aware thjqt the first - and possibly the greatest - error lies in reading the test meter? All meters should be indicating as near as possible to their f.s.d. ?

Ken Green
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13 May 2013 09:29 PM
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ectophile

Posts: 400
Joined: 17 September 2001

Lorna:

That working looks right to me.

Ken:

By the sound of it, that's a digital and not an analogue meter. So the concept of FSD and meter reading errors wouldn't really apply.

-------------------------
 S P Barker BSc PhD MIET
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14 May 2013 06:28 AM
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g3xoi

Posts: 2569
Joined: 13 September 2002

Add AND SUBTRACT the 2%. because tolerances and errors are usually +/-..

Mind you, it could be worth carefully re-reading the spec because with a digital meter you should not have a reading error - it is reading 15.5 v or it is not. As ectophile says....... There is no parallax error as with an analogue meter

-------------------------
Alan

n.b. This message has a limited shelf life.
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14 May 2013 09:24 AM
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cblackha

Posts: 48
Joined: 21 January 2003

Accuracy = ±5% ±2 digits

That might be
Accuracy = ±5% or ±2 digits - which ever is larger (rather than both).

The values you have been given are the nominal values given by the manufacturer and don't necessarily reflect the machine you have - do you have, or can you get, the calibration certificate?
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14 May 2013 01:19 PM
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kengreen

Posts: 72
Joined: 15 April 2013

Hi to All,

I seem to have sparked quite a discussion - and who can complain about that?

It was mainly that Lorna's question reminded me of the budding amateur who settled on my visitors' stool, examined my Bench and then enquired whether he should purchase a digital or an analogue meter? My attempts to explain obviously were confusing him
and I deemed it best to let him grow a little.

Ken
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