cold junction calibration

[L-king]

Hi,

Can anybody help me with cold junction calibration? I am using an excel sheet developed by some student couple of years ago. I am using a k type thermocouple and what i could understand from the excel sheet is that it reads set of temperatures and prt temperature.

this prt temperature is converted to prt voltage by some non linear equation (using four constants), which makes no sense to me.

the acquired temperature is then converted to voltage and added with the prt voltage. this voltage is again multiplied by the same constants to get the correct temperature.

these constants have been changed for experiments conducted on different days.

Any advices will be greatly appreciated. Also, if possible please give links to the theory behind this.

cheers

vinod

[devchander]

Hi Vinod,

These two links will give you info on cjc and voltage to temperature conversion

http://zone.ni.com/devzone/conceptd.nsf/webmain/b886eca5994aa782862568650068fcea

http://digital.ni.com/public.nsf/allkb/e332e1d829059fb5862570ae005066b3

Regards

Dev

[Henrik_Volkers]

One starting point is
NI Developer Zone > Development Library > Sensors > Temperature > Thermocouples

Another good source is the omega handbook.

My personal fav. is 'Manual on the use of Thermocouples in temperature measurement' (ASTM Manual Series MNL 12, ASTM PCN: 28-012093-40).

 Quote Page 1:
"Regardless of how many facts are presented herein and regardless of the percentage retained, all will be for naught unless one simple important fact is kept firmly in mind. The thermocouple reports only what it 'feels.' This may or may not be the temperature of interest."