What is the difference among J and K type thermocouples? Can some one tell?? How to calibrate the thermocouple efficiently? why a J type thermocouple is preferred over the K?

 

They work through different temp ranges
you can use any digital temp. controller for accurate reading.

Mick

 

If you look on the Omega web site you can a good bit of information.

http://www.omega.com/temperature/Z/zsection.asp

In short J is cheaper but has a smaller useable temperature range. If the temperature is above 760C do not use J.

Since thermocouples are just wire you cannot really calibrate them, you can just measure their exact response and use that information in your controller to get the best accuracy.

Efficiency depends on what you want to obtain, how often you do it, and so on. Often the most efficient is to have the supplier do it. But then you have to pay him for that service.

James Bouchard

 

The difference is in the materials used to build the thermocouples. J type T/C's have an iron wire in one leg and in our case we find this rusts in humid weather. The rust causes inaccurate readings and at worse open circuit. Exact wire materials used can be found with a little web searching.

 

James, your right on with this one. Chandra, Omega offers TC simulators, you can use this device to calibrate the temperature input of your controller, PLC, SCADA system or whatever your connecting to with the TC. Then just hook up the TC. Once you have connected the TC, you can use a 3 or 4 point calibration check with a small temperature bath. Omega also sells calibrators which have 2 or 3 point capability, since your only checking the respons of the TC that would be good enough as the simulator has already calibrated the controller input channel.

Matt Hyatt

 

in J type thermocouple iron-constantan material used and in K type thermocouple cromel-alumel used.

In thermocouple, two different material wires used to make a junction.

In J type thermocouple, it gives 1 mV output for 18 deg C and in K type thermocouple, it gives 1 mV output for 25 deg C.

J type thermocouple used for 0-600 deg C and K type thermocoule used for 0-1273 deg C.

 

Be careful in the type you select:
Temperature range is a little different for each type... you must select the appropriate type for the range you are looking for.

Also... the composition of the junction is different for each type.

I had a case where the J type was fine for the temperature range but was in a corrosive atmosphere... the iron in the junction would oxidize and the T/C would fail... had to switch to the K type and had no more corrosion problems.

Gerald Beaudoin

 

In my early days in this business I worked for Surface Combustion, designing Industrial Furnaces. As I remember, type J T/Cs would oxidize at about 1500 deg. F so we limited their use to Aluminum ingot heating and similar if exposed to air. They would work in an atmosphere furnace (using Nitrogen gas) to a higher temperature but you will see in most reference data a limit specified at 1400 deg. F.

Anything we did with steel that required 1700 deg. F and above used type K. An except to using type K was at the top end of our design temperature range which used type R or S. These T/Cs uses Platinum and Rhodium and obviously can cost a bit more.

At that time (late 1970s), calibration and compensation for non-linearity was a much bigger issue than today. Most any T/C transmitter available today does a good job of providing a linear output and are able to input several common T/C types. In the references listed above are several T/C calibrator devices which should allow you to check the transmitter output for your desired range.

Regards,
Russ Kinner
Rockwell Automation
Phoenix, AZ

 

Have you heard of a Rockwell thermocouple with a part# N116000270-01-60 Type K? I am looking for 4 pc.

 

> James, your right on with this one.

YOU'RE right...