Calibration of the spot welded TC wire thermocouples

[homoly]

Hello,

I would like to ask you what is your policy of calibrating TC cable based thermocouples. Is the initial calibration done by some third party certified body and the verifying is done internaly, all check are done by certified body or everything beginning with initial calibration is done internaly?

My next question would be what shall be the period of checking and what equipment do you use for internal verifying. Are there some relevant standards ( or literature ) that could provide a guide for this process for me?

Gabriel.

 

[moltenmetal]

Presume you're talking about thermocouple wire, not thermocouple EXTENSION wire. While it is possible to make a thermocouple from extension wire, it's a fair bit different than making them from properly spec'd wire.

 

[homoly]

Yes the question is about thermocouples made from TC wire. But anywaway my question should be valid generally for all thermal sensing equipment which is not supplied by a third party manufacturer who supplies the calibration protocol on request.

 

[skibum2b]

We build thermocouples and calibrate them here, so this "rule" is based on what we do here.
Usually the check is made by the person/unit who supplies it, whether internally or by a 3rd party.
When a specific class or specification is required, the buyer may choose to outsource it to a certified lab (or have us do it, and report the results).
Some labs are NVLAP certified (which means they have measured and certified the amount of uncertainty in their system), though all calibration labs should have a "standard" that is traceable to NIST.

 

[MintJulep]

Rather than asking others what their practices are you should be asking yourself what your requirements are?

How accurate do you need your temperature measurement to be?

What are the potential consequences of an inaccurate measurement?

There is more involved than just the calibration of the T/C itself. You need the complete metrology chain calibrated.

 

[homoly]

skibum2b: Only one question - what kind of device are you using for internal calibration: calibration oven or (artificial) ice point ?

MintJulep: We have normally everything under control but I have discovered this weak point in the company ( only the datalogger was calibrated until now ). As a first step I had collected all the soldered TCs and will sent it to spot welding which is a must for eventual thirt party calibration.
My question was internally what would be the requirements to check the reliability of the TC. If it is enough to check for example only at the room temperature in some isolated space comparing with some Pt RTD reference or even the internal checking should involve more measuring temperatures.

Of course it is no problem for me to arrange the 3 point calibration with external lab, but I was curious about some real world internal TC checking example when the external calibration by certified lab is not the requirement ( i.e. by customer or another lab for product safety evaluation ).

 

[Compositepro]

Homoly, go to the Omega Engineering website. They have an excellent handbook on thermocouple technology and they sell calibration equipment so you can see how it is done. To calibrate thermocouples themselves you need accurately calibrated temperature baths. The meters are calibrated with voltage sources.

 

[homoly]

Compositepro;

Thanks for the Omega link I will check it out. It is clear for me that the datalagger is calibrated with voltage that was the reason of my question about the TC calibration. I will check the Omega baths, thank you very much for the hint.

Gabriel.

 

[EdStainless]

We used to make our own in house. We would make a group from a new batch of wire and send one out for cal verification. We would put all of them into a bock in a lab furnace and make sure that they matched each other. We sometimes for a 'stray' in the group.

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