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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
 13 May 2013 02:29 PM
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kengreen

Posts: 400
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
 13 May 2013 09:29 PM
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ectophile

Posts: 552
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
 14 May 2013 09:24 AM
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cblackha

Posts: 79
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?
 14 May 2013 01:19 PM
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kengreen

Posts: 400
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
 03 July 2013 12:51 PM
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BrianHoskins

Posts: 2
Joined: 12 August 2011

Hi Lorna,

Your calculation of the measurement uncertainty looks correct to me. It is indeed a case of first calculating the uncertainty due to standard accuracy (in your case 5%) and then adding on an additional uncertainty to the least significant digit (in your case 2).

I wrote a small article on this on my personal blog some time ago: http://www.brianhoskins.co.uk/...l-multimeter-accuracy/

-------------------------
Brian J Hoskins BSc MIET
Test Development Engineer & Electronics hobbyist
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 03 July 2013 03:15 PM
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BrianHoskins

Posts: 2
Joined: 12 August 2011

Ooops - I only just realised this topic is over 1 year old! I neglected to look at the year of the post. It seems that a few of us made that error. Anyway, I will leave my response there in case any one else finds it useful.

-------------------------
Brian J Hoskins BSc MIET
Test Development Engineer & Electronics hobbyist
PERSONAL WEBSITE
TWITTER
GOOGLE+
 14 September 2013 04:03 PM
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remon7

Posts: 1
Joined: 11 August 2013

PAT is used to describe the check of electrical appliances and equipment to ensure they are safe to use. Portable appliance testing.
Earth Bond Test should show less than 0.1+R Ohms. where tested current 1.5 times. Insulator Resis, applied test voltage should be approximately 500 Vdc. But your Step:1 Calculation seems wrong. If you want to get more calculation about Electronics Calculator. usually solved thousand's of Electronics Calculation by using this tools.
Thanks
Eng Remon
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