Test gear and calibration

[Golden_Boy]

How accurate must test equipment be in order to satisfy the regulations?

The reason for asking this question is that I now have access to 3 bits of test gear for Insulation and continuity testing. If I use a 1% tolerance 10Mohm resistor as a test item I get 3 diffrent results from the bits of gear. One is a Megger, one a seaward ant the third is a fluke. The fluke is the most accurate with the others being about 8% wrong ( reading low ). If I then use 2 multimeters and ohms law the result is almost exactly 10 M ohms.Similar differences appear on the "low ohms" ranges with a 1 Ohm standard resistor!

When "calibrating" items of test gear what adjustments are made as looking inside say the megger there appear to be no adjustmets at all?

 

[Megger TSG]

Hi

17th Edition test instruments have a basic accuracy of 5%
A Megger insulation tester can have an accuracy of plus/minus 3% plus/minus 2 digits
This means, in theory, two Megger testers can have a 6% difference and both still be within published specs.
A competitor product maybe plus/minus 5% which means a 8% difference to a Megger is feasible.

It is recommended to consult manufacturer data sheets and particular cal certs for specs.

Regarding calibration, the days of tuning "slugs", tweaking pots and sealing wax are long over, calibration is now digital
making test instruments more robust in everyday use.

Regards

Megger TSG

 

[Golden_Boy]

Hi

17th Edition test instruments have a basic accuracy of 5%
A Megger insulation tester can have an accuracy of plus/minus 3% plus/minus 2 digits
This means, in theory, two Megger testers can have a 6% difference and both still be within published specs.
A competitor product maybe plus/minus 5% which means a 8% difference to a Megger is feasible.

It is recommended to consult manufacturer data sheets and particular cal certs for specs.

Regarding calibration, the days of tuning "slugs", tweaking pots and sealing wax are long over, calibration is now digital
making test instruments more robust in everyday use.

Regards

Megger TSG

Thanks for the information.. As I said there did not appear to be any adjustments ( or Data ports ) on the kit I looked at ( probably too old LOL) I assume with the up to date kit its a matter of electronicaly tweeking the dividers or whaever to match the standard instruments reading. It would be interesting to find out how it was done before data ports and with no pots to tweek?

Thanks again for the information

 

[nrbspark]

I have had a set of 3 Robin testers Ins/Cont, RCD and Loop/Psc for 9 years now, they get calibrated every 12 months and in house checked quarterly. According to the calibration certificates issued they have never had a fail or adjustment, so if you are looking for a reliable set of testers I recommend Robin every time.

1 question that I would throw into the mixer is what if the calibration equipment is faulty or out of tolerance, does the calibration equipment need calibrating? and where would it end?

Its like the question what came 1st the chicken or the egg?

 

[Golden_Boy]

I have had a set of 3 Robin testers Ins/Cont, RCD and Loop/Psc for 9 years now, they get calibrated every 12 months and in house checked quarterly. According to the calibration certificates issued they have never had a fail or adjustment, so if you are looking for a reliable set of testers I recommend Robin every time.

1 question that I would throw into the mixer is what if the calibration equipment is faulty or out of tolerance, does the calibration equipment need calibrating? and where would it end?

Its like the question what came 1st the chicken or the egg?

It certainly makes me wonder whether the " calibration services" are worth the money ?
If as you say your robin has never needed any calibration at all! Just a quick check, print out the cal certificate and pop the dosh in the bank!!

I have done a bit of research and apparently the Standard equipment used to check / calibrate instruments needs to be 10 times more accurate than the kit being calibrated so goodness knows what they calibrate THAT with !

 

[Megger TSG]

Hi

The equipment used to calibrate test instruments has to be very accurate and is traceable to industry standards. The equipment is checked and cross checked on a regular basis to ensure accuracy.

Regards

Megger TSG