thermocouple types

C

Curt Wuollet

http://www.omega.com

This is not a sales recommendation. These guys have put a great deal of effort in to collecting useful information about measurement gear and publishing it free in their catalogs. I believe they make it available on the net as well. The difference is in the metals used for the pair which gives a different voltage out and makes each suitable for certain applications. I usually reach for their catalog whenever I have a question. I also buy stuff from them occasionally.

Regards

cww
 
The main difference is the metals used in the conductors. Type J uses Iron and Conatantan conductors. Type K uses Chrome and Alum. The different metals offer diferent thermocouple effects. The color code also differs. Type J uses red (-) and white (+). Type K uses red (-) and yellow (+).

Hope this helps.
-Jason
 
M

Mike Johnson

Type J uses an iron wire and a Constantan wire. It is often used for applications from 0-600C. The connectors are black. Type K uses Chromel and Alumel wires. It is often used up to 1250C. The connectors are yellow. J and K make up the majority of the thermocouples that are used for many standard applications.

Regards;
Mike Johnson
[email protected]
 
J type is iron/constantan and K type is chromal/alumel. They generate different voltages and have different curve characteristics.
K type is generally preferred as iron has a marked tendency to rust out.
Obtain a set of curves from an instrumentation company that produces temperature controllers and you will be able to see the difference in the curves.
 
Hi Mike

Can you tell me how can i choose thermocouple with batter tolerance means that +-1 or +-2? I already know that type J, K is for the temperture, and what about the tolerances?

Thanks a lot
Eliran
 
M

Matthew Hyatt

Eliran

The measurement tolerance is going to be more based upon the device used to read the temperature. The TC themselves have a very defined curve related to the properties of the metals used.

go to http://www.omega.com

Thay have great technical reference material.

MJH
 
C

Curt Wuollet

When you need this type of accuracy with a thermocouple, you need to account for quite a few factors and then individually calibrate the thermocouples. That's why RTDs are typically used when TC accuracy isn't adequate. (and money is no object) Due to many factors like metal purity, inline thermal gradients, CJC accuracy, etc. TCs can vary somewhat more that RTDs. That's why they are sold to comply with an envelope rather than absolute accuracy specs. Even wear on a plated conector screw can give you grief at these accuracy levels.

Regards

cww
 
In some case of application can use K or J, but the output voltages are different so that you must change the parameter input type in your temperature controller.
 
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