Calibration of Equipment Timers

[PFISTO]

Good morning,
Ok so after doing some long searching I was unable to find a direct answer to my question which is:
We have many centrifuges in which we calibrate the time. Up to this point we have been using a calibrated stopwatch to perform this event I believe the direct comparision method in which the centrifuge timer and stop watch are started at the same time. I am wondering how other people would perform this calibration as far as to how many points to do or for how long to time for. I have read many articals in regard to the human error 300 ms, but would like to know. Our tolerances are based on the mfg specs.
Thanks Mike

 

[BradM]

Hello there!

Here is a nist reference that may help.

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=50659

Generally, we calibrate our timers using the oscillation/frequency standard, and claim ?1 second accuracy. Then we test field devices to ?2 Seconds.

Hope that helps!

 

[PFISTO]

Yes I have that document and have gone thru it but I was not very clear as to how it spoke to doing a calibration with a stop watch looking at a display, which is what I am referring to. It does say something about 1500 sec I believe which may relate to my question.
Mike

 

[BradM]

We verify process equipment in the same manner that you specified. We start and stop them together.

Generally for centrifuges, we will verify the time based on their process use (5 min; 30 min; etc.). I'm not sure about mfg. specifications, but I would suggest establishing the tolerance as a percentage.

 

[dgriffith]

Yes I have that document and have gone thru it but I was not very clear as to how it spoke to doing a calibration with a stop watch looking at a display, which is what I am referring to. It does say something about 1500 sec I believe which may relate to my question.
Mike

The above document, NIST SP 960-12 Recommended Practice for Stopwatch and Timer Calibrations, has something on this in Section 9a, Table 13. Reread it and see if it helps.