Urgent Help With Calibration Issue AMS 2750

[bwdreiko]

Hi there, we were using external calibration house to calibarte all ours furnace in accordance with AMS 2750 Rev E, we discovered that they were using on field equipment (T/C calibrator) to calibrate on field recorder and TUS thermocouples.During NADCAP audit we had NCR for the fact that on field calibrator wasn't calibrate on correct thermocouples types in this case type N.
what you can see on COC of field test equipment was done on type K thermocouple to cover range between 0-1100*C and on type N to cover range from 600-1000*C.but they used this equipment to calibrate TUS recorder on type N thermocouple on the range from 100 to 550*C and they did the same for TUS recorder(auditor base on this invalidated 10 surveys). Is it acceptable???we contacted calibration house and they replaied that it does not metter as calibartor was calibrate on 0-1100*C on type K and has been found to meet criteria so it must work on diffrent types to
any comments would be appreciate

 

[dgriffith]

we contacted calibration house and they replaied that it does not metter as calibartor was calibrate on 0-1100*C on type K and has been found to meet criteria so it must work on diffrent types to
any comments would be appreciate

I would have to agree with the calibration house. The calibrator is a millivolt source and measuring instrument. If it is calibrated over its stated specification, say a (-13 to 80)mV range, then any thermocouple should be correct if the TC output is within that range.
The TC type (K, N, T, etc.) is just a conversion and is usually preprogrammed and has little to do with voltage calibration of the calibrator.
The N-type voltage for the range of temperatures of (100 to 550) ?C (2.774 to 18.672)mV is within the K-type calibrated voltage range, (0 to 1100) ?C (0 TO 45.119)mV. As long as the calibrator conversion isn't malfunctioning, it should source and measure correctly regardless of TC type.

 

[MTProcessing]

I am sure the instrument works correctly as it was calibrated.

That said, AMS2750E requires all the thermocouple conversions to be on the calibration certificate, 6 temperature points spread over the range of use for every thermocouple type used. However little it makes sense, that is the requirement.

Your contractor needs to start having this information put on the instrument certification every time it is calibrated.

 

[dgriffith]

Aha! A fly in the ointment . . . Sorry about that.
So, the customer should communicate this to the calibration service provider, giving him his requirements, and while the instrument capability is there, the governing document requirement was not met.