Test Instrument Calibtration - How frequently ?

[kwikfix328]

As per thread title.

Q: Legally, How often do you have to get your test instruments calibrated ?

Q: What is considered to be good practice for an instrument that is used infrequently ?

I know that the calibtation houses will recommend that they are done annually , however they are running a business and so even though it is probably a good idea, I would expect them to say that , (for the return business) anyway.
We will all know that an instrument can only really be considered accurate at the exact moment of calibration anyway.

At my work place we usually get at least one internal audit by the Quality Manager and the senior Maintenance Manager and at least 1 or 2 external quality audits by the CAA ( Civil Aviation Authority) per year to ensure we are maintaining at least the minimum required standards. The Instrument & tool calibration register is something that always gets close scrutiny.
Needless to say any time i 'really' need to use a specific tool it will be away on Cal too

I have just bought a brand new RCD tester and s/h Loop tester (annual cal expired 19 dec 2007) and a s/h Cont/Ins tester which hasn't arrived yet, but is out of cal too. These will be used for private/Home/DIY/ Personal interest purposes - not professional

so just asking out of interest really.

 

[ban-all-sheds]

Q: Legally, How often do you have to get your test instruments calibrated ?

In a domestic context there is no specific requirement.

Q: What is considered to be good practice for an instrument that is used infrequently ?

The same as one used all the time, I guess.

You can either:

1) Have them calibrated every year, or more often if you have reason to think they are not OK.

2) Make up a small box containing a selection of high and low resistance values taken to 4mm sockets or binding posts, a socket with a 1 ohm resistor switchable into the earth path and an RCD - the socket & RCD connected to a flex with a 13A plug.

Use good quality high stability components and sound construction techniques.

Have your instruments calibrated and as soon as that is done use them on your check box and measure IR values (high resistances), continuity values (low resistances), the difference in loop resistance with & without the 1 ohm resistor, and the RCD values. (Obviously you'll need access to a non-RCD socket to plug into).

Log the date and values.

Periodically, and before each use of the testers, repeat the tests. As long as the readings you get are the same then you know that your testers have not drifted off.

If the results have changed, then go for recalibration, and if when the testers return you find that the results are still different then kick the check box around the garden and build a better one.

Tip - ring around your local wholesalers and see if any of them have any calibration days coming up.

 

[kwikfix328]

You can either:

1) Have them calibrated every year, or more often if you have reason to think they are not OK.

2) Make up a small box containing a selection of high and low resistance values taken to 4mm sockets or binding posts, a socket with a 1 ohm resistor switchable into the earth path and an RCD - the socket & RCD connected to a flex with a 13A plug.

Use good quality high stability components and sound construction techniques.

Have your instruments calibrated and as soon as that is done use them on your check box and measure IR values (high resistances), continuity values (low resistances), the difference in loop resistance with & without the 1 ohm resistor, and the RCD values. (Obviously you'll need access to a non-RCD socket to plug into).

Log the date and values.

Periodically, and before each use of the testers, repeat the tests. As long as the readings you get are the same then you know that your testers have not drifted off.

If the results have changed, then go for recalibration, and if when the testers return you find that the results are still different then kick the check box around the garden and build a better one.

Tip - ring around your local wholesalers and see if any of them have any calibration days coming up.

seems like sound advice and a new little project to get my teeth into, will look into this further.

Thanks.

 

[lazygit]

Maybe this can help:

http://www2.theiet.org/Publish/Wire...ters_ongoing_accuracy_of_test_instruments.pdf

Regards

 

[kwikfix328]

Hello,

Been giving this a little more thought and have come up with a little schematic/plan as illustrated below:

One of my problems is that i don't have any non RCD protected sockets in the house any more, however I do have a couple of spare ways on the non RCD side of my CU and so could set up a dedicated single socket outlet, possibly a lockable one so it only gets used by me just for test purposes. I do have a number of RCD plug adaptors still fitted to power tools, etc, so it would also be handy for testing these.

I know that you can buy commercial versions, but they seem to be just as expensive as the test instruments themselves. I plan to get my s/h testers calibrated once I've got a suitable check box either made or bought.

Any useful comments greaty appreciated, (especially regarding suitable resistor values/specification).

Untitled

• kwikfix328
• 29 Apr 2008
• 1

Idea for a calibration test box. <br>So that i can periodically check my instruments prior to...

 

[ban-all-sheds]

Looks good. IMO an RCD in the check box would be more elegant, but if you've got some plug in adaptors then that elegance comes at a price.

If you're going to use a dedicated socket you might as well use that for loop testing, and dispense with the socket & switchable resistor in the box - there's only any point in having that if you want to be able to use any old socket, and you therefore want to check that the 1ohm delta remains constant...

Resistor values - I'd try and get the high values up to 500M.