Thermocouple calibration

Hi all,

Need some explanation regarding the following. We have some gas fired ovens in the facility that have type J thermocouples installed. The signal is fed back to the pLC rack where the PID temp loop takes over and sends temp value to HMI screen. The question came up for a potential medical customer as how do we know our oven temps are accurate and actually reading the correct temp. This leads me to investigate how we can accomplish this and show that they are reading accurately as we have never done this before.We have a calibrated thermocouple simulator in house but we have no calibrated thermocouples. Can anyone explain how best to go about verify the temp accuracy and also what is the difference between a calibrated and non- calibrated thermocouple. Thanks

If your customer is from a medical company then they are probably regulated by the FDA who have stringent guidelines on calibration.

Calibration is confirming something works against a known standard. To calibrate the thermocoulpes you will need to use a calibrated temperature standard.

I agree with the above.

http://www.astm.org/DATABASE.CART/HISTORICAL/E220-02.htm

Here (food industry) we use an ice bath to check temp sensors at 32 degrees F, and a calibrated comparison thermocouple/thermometer to check the sensors at a temperature closer to the operating range or the limits of the sensor.

What temperature range are you operating ovens at?

I think it is almost OK to trust TCs as is unless broken DEPENDING on your accuracy requirements ie OK for +- 2 or 3 degrees.

I did oven checks in aircraft industry. Made own thermocouples up. Inserted multiple TCs ie say 9 at representative locations in oven. Heated up and recorded data with data logger. Temperature variation specs varied depending on oven use 500 F to 1900 F. Had to have 20 minutes of data where they met this spec. They all had to be within the spec tolerance or we had to do something to oven to get them all to agree. Generally the door seal was biggest problem.

Dan Bentler

www.hartscientific.com/products/9100S-9102S.htm
This is what we use to calibrate the oven probes.Fluke 9100s