AMS2750 Secondary Instrument, what am I doing wrong?

[badbascom]

I heat treat aerospace parts at 500-1300°C. AMS2750 requires ±0.2°C or ±.05% accuracy for secondary instruments. I cannot find any instrument on earth that meets this requirement for Type S and at some temperatures of the Type K & N. I have three Fluke 5522As, Fluke data sheets states uncertainties in the ranges of .36-.37 for Type S, and .26-.4 for type K. TEGAM states their 945A meets AMS2750 secondary because their accuracy is ±.005% of reading ± 5 uv, however in the same data sheet they have maximum uncertainties for each thermouple types and uncertainity exceeds AMS2750 for Type K at all temperatures. Based on the fact these Fluke 5522a's are common in calibration labs, am I interpreting the data sheets correctly?

My 2nd question is if I am calibrating a Type S channel on an instrument and the calibrator is simply outputting a mV, how is the accuracy worse for this Type S than if I was calibrating a Type K channel?

Thanks for any advice on this, I hope I explained my situation correctly.

 

[Randall Beck]

To help me understand your question - what exactly are you using your secondary standard for? Calibration - SAT - TUS - Recording - Control?

 

[badbascom]

I will used the Secondary Instrument to calibrate Field Instruments. Since posing this question I have learned the Fluke 5522a is capable of much tighter tolerances than the maximum permitted error published by Fluke. I beleive the path is to develop a custom calibration for our 5522a which specifies my applicable temperatures and thermocouple types. Unfortunately, it appears Fluke standard calibration procedure only calibrates to the J type.

 

[Randall Beck]

Correct. Your secondary standard must remain in your lab and used to calibrate your in-house Field test Instruments. I do the same thing and have a custom form that accounts for all correction factors, temperatures, thermocouple types, sourcing, measuring etc. It is custom calibration form for my specific calibration needs. I think you are good in your application. I use a Piecal 422 as my secondary standard that I send out annually that stays in my lab/office and Fluke 714B and 714 for my in-house field test instruments for the shop use. Never had an issue during calibration or NADCAP audits.