Checkbox question

[ban-all-sheds]

Here's a guide to a 'DIY' checkbox from another forum:
http://www.talk.electricianforum.co.uk/showthread.php?t=12[/QUOTE]
Should I ask WelshWizard there, or here, about the discrepancy between an IR tester zapping out 500V, and a reasonable expectation of results in the 100's of Mohm, and the use of 4mm sockets rates at 60V with an IR of <3Mohm?

 

[BS3036]

Should I ask WelshWizard ...

Well, before you do, I should measure the resistance between two points about 2cm apart on a plastic box of the type he's using. I would be surprised if there was a problem.

I'd be more concerned about the 250V max rating of the resistors. It's not easy to get better resistors, but the ones I got from Rapid were something like 500V but only for an unspecified short time. Mostly I put more than one in series.

 

[ban-all-sheds]

Now there's a point.

The voltage rating of the sockets is something I've been paying attention to because I'm mounting mine on a metal panel - I guess on plastic ones it's less of an issue...

 

[BS3036]

...I'm mounting mine on a metal panel ...

You got me to thinking there (as I've nothing better to do after a hard day's chasing into thermalite block). If you make your tester/checker as if it could be a saleable product, out of principle perhaps, rather than actually planning to sell it, (which is how I always work)...

How are you earthing or otherwise ensuring safety with a metal panel? You couldn't really require that the product must be connected to a earthed supply as people wouldn't bother if it was just a high resistance measurement check.
The only alternative seems to be to meet the class 2 requirements (double or reinforced insulation) which is adding to the design problems unnecessarily. A plastic panel seems to solve the problem in the most economic way.

Just a thought

 

[securespark]

My test resistors happen to be high stability 1% types. Note: My check box is actually a few of these with one end twisted together and taped with stick backed plastic - some say I don't take this subject seriously - but what do they know

It may work, but it's a bit tacky....

Dreadful pun, BAS, dreadful...

 

[ban-all-sheds]

How are you earthing or otherwise ensuring safety with a metal panel?

By earthing the metal plate.

Mine will have an RCD, and a socket for doing loop tests, and therefore will need to be plugged in.

You could check IR and continuity functions without plugging it in, but then you could attach one croc clip to each testicle and send 1000V down the leads...

I don't mind making a safe item, but I'm b*gg*r*d if I'll spend time making it impossible to abuse.

 

[BS3036]

 

[ban-all-sheds]

Plus I doubt you could make a "boxed" version all in for less than the price of the cheap and nasty product I am spamming!

Actually you probably could make one that only did IR and continuity, and only had pads for the probes, for less than that - the expense comes in decent 4mm sockets, and resistors that can cope with loop-test currents.

but this isn't about price, or ease - I shall enjoy making it.

And mine will also do loop and RCD tests.

 

[calltronics]

When a product designer replies to a forum it is difficult not be reported as spam by other less objective people. However, what this forum and some of its contributors have inferred, or in some cases stated, are now seriously miss-leading other members off on potentially wrong paths.
“Checkboxes” are what their name implies....
A checkbox is used to ensure that an instrument measurement ability(whatever value that may be) when it returns from calibration, does not wander/drift over the calibration period.
It also can function as a simple check measurement when an electrician doubts his meter readings and requires simple verification.
All the commercially available checkboxes are not meant, nor do any claim, to be used as calibration reference sources, in order to extend the calibration of an instrument or in fact actually calibrate an instrument, as some have hinted at.
They are simply CHECKBOXES.
So ...........
The most important factor in checkboxes is not the absolute resistance measurement, (resistance tolerance figures) it is the relative measurements from the first reference measurement on the instruments return from calibration remains the same throughout its calibration period.
Therefore the priority of the design of all calibration checkboxes must be to ensure that the DRIFT in resistance measurements was minimal through the instruments calibration period (normally 1 year).
Twisting resistors, wire and tape is totally wrong. Try maintaining stability over one year it simply is impossible and does not work. Twisted connections will vary simply by the tarnish and mechanical stability of the joint.
The use of high tolerance resistors is not necessary. WHY? It is the repeat measurement you are interested in not the absolute. Tolerance figures do not have any baring on stability. High tolerance resistors are resistors from the same batch which when measured are found to be in a tighter tolerance range than the manufacturing process tolerance, (aka - the cream of the batch). The resistors stability, voltage, current are not affected by the resistors tolerance. So don’t waste money on high tolerance resistors, they simply are not required, standard specified resistors are adequate and maintain their repeatability well within any electrician’s measurement instruments range.
Lastly but not least………
Yes, I agree with all those people who say and recommend you make your own. Get the connector bocks/soldering iron out, buy some cheap resistors, (look at resistor values of commercial checkboxes), and make one. If you want to and have the time splash out further put them in a box with 4mm sockets. These are all good solutions and they will work. Every inspector will accept them and agree they are suitable for ensuring the correct operation of the instrument throughout its calibration period. So long as you can demonstrate you regularly check and record your measurements.
The CalCard does not claim to better, superior or a calibration reference source just simple one of many accepted solutions to facilitate a calibration checkbox.
Every checkbox on the market is simply as contributors have so much stated “a collection of resistors”! All I did was spend a lot of money on tooling, design and patent to enable a surface mounted solution. This in turn enabled electricians in the field to have a credit card size device that fitted into instrument cases with the instrument where it was needed, nothing more nothing less.

 

[ban-all-sheds]

When a product designer replies to a forum it is difficult not be reported as spam by other less objective people.

C'mon - be fair - your original reply didn't have any of the material this one did, it was just plugging your product.

“Checkboxes” are what their name implies....
A checkbox is used to ensure that an instrument measurement ability(whatever value that may be) when it returns from calibration, does not wander/drift over the calibration period.

If you look at any of my posts on them you'll see that what I've always said, and AFAICT most people understand it anyway.

Tolerance figures do not have any baring on stability. High tolerance resistors are resistors from the same batch which when measured are found to be in a tighter tolerance range than the manufacturing process tolerance, (aka - the cream of the batch). The resistors stability, voltage, current are not affected by the resistors tolerance. So don’t waste money on high tolerance resistors, they simply are not required, standard specified resistors are adequate and maintain their repeatability well within any electrician’s measurement instruments range.

You do need them to be reasonably stable though.

The CalCard does not claim to better, superior or a calibration reference source just simple one of many accepted solutions to facilitate a calibration checkbox.

I don't think anybody has been criticising your actual product...

 

[NotHimAgain]

I don't think anybody has been criticising your actual product...

Maybe not, but he criticised my check 'box' - doesn't he realise that the sticky backed plastic that I used is actually highly stable Sellotape .

 

[ban-all-sheds]

Quite right too.

Everyone knows you should use Blu-Tak, as that encapsulates the joint...