Thank you sir that was a very informative explanation which i learned from now. So I can decide the tolerance basing on our process? how do i support this during audit.
George has a good post here, to show the thought process that you should go through to determine a tolerance. He did a good job of coming up with
tolerance of specifically +/-0.5kg +/-0.5% of reading
That might be a good start for you.
You really should be writing up and documenting the process you are taking towards deriving your tolerance and such.
As far as the auditor, it all depends on the auditor, industry, etc. But in general, if you have documented the rationale for the tolerance, and it satisfies the process/customer requirements and is being done according to your calibration procedure and such, I don't think an auditor would have a huge problem.
Determining calibration tolerances for me, is as much as an Art than a Science. While mfg. specifications are a good start, many times they are set too tight (for marketing purposes, in my opinion) and thus, you start having a bunch of failures.
Consider that you have a 500 gram balance, and the mfg. tolerance is .0005 grams. You find an error of .001 grams, so technically it's out of tolerance. Yet... you are weighing a product and the critical parameter is 75 grams +/- .01 grams. Did that error that was found have any impact on that parameter? No.
So in that instance, I might set the process tolerance to .005 grams, which the balance should be able to meet.
So, determining what the balance is going to be used for, can give you some guidance in determining what is an acceptable tolerance. It can also guide you if you have the wrong equipment for the process, which happens too.
