Vision system calibration standards- need for annual recertification

[AnalogKid2DigitalMan]

Cross-posted on the dark side at:

Hello All:

Questions and guidance regarding chrome-on-fused silica targets used to calibrate vision systems:

We have a couple of these at our facilities and in order to satisfy ISO requirements, some people internally insist these must be sent out yearly to be ‘calibrated’ (re-certified is probably a better term). Since they are not subject to wear akin to rulers, scales, pin/plug gauges, I see no need to have this done. They are a pattern of squares and circles of various sizes, typically ranging from 0.0005” to 0.5” and have been measured at the time of manufacture to within +/-.00001” and 0.00002” uncertainty. Coefficient of expansion is a negligible 0.5ppm/C. Unfortunately, the companies that fabricated and measured the standards (P.P.L/Align-Rite and Optronics Specialty) have moved on to other lines of work and I cannot get a statement from them to back up my position. The last time we sent one out, it almost was lost in transit and then took 3 months to get it back.

Anyone else have experience with such matters and how did you handle it?

Other than NIST, any suggestions of companies that can certify such standards since I would like to get a tighter uncertainty measurement on one of the standards.

Thanks for your feedback!

-AK2DM

[PaulG.]

If you can no longer get in touch with the manufacturer for their recommendation the safe bet would be to get them re-certified. An ISO auditor can always ask: "How do you know the targets are still calibrated"? Can you re-certify them internally with another certified instrument?

[B Grey]

I believe, if you actually check what the ISO standards say about calibration frequency there's some clause to the effect of "as necessary." Some things need calibrating weekly and others never. I think it's perfectly acceptable to argue to your auditor that since a calibration grid or target is not subject to wear it doesn't need to be calibrated. (I used to do that long ago when I had ISO9000 responsibility.)

As regards who to ask about calibration - Max Levy are the guys. http://www.maxlevy.com/SupCat.cfm?SCID=2

Let us know how you get on.

Brian.

Blogging away on vision at http://machinevision4users.blogspot.com/