Wire between thermocouple and transmitter

[Pitt123]

What type of wire is supposed to be run between a thermocouple and a transmitter? I believe its three wires, but is there a particular size or type that is standard? Will a regular #16 or #18 shielded triad be sufficient?

Is it general practice not to use fork lugs when connecting these wires? Any problems with doing so?

 

[nakulak]

http://www.hotektech.com/DeltaOhmHD778TR1.htm

 

[don_resqcapt19]

The wire needs to be thermocouple extension wire and any terminal points need to be made for use with thermocouples. The extension wire is different for each of the types of thermocouples, example type J or type K to name two. You need to take care with keeping these cables isolated from cables of other systems to prevent errors.

 

[sawdust454]

Also you will notice the thermocouple extension wire contains a red and white wire. The white conductor terminates to the + terminals and the red to the -.
The extension cable comes both shielded and unshielded. I typically recommend the shielded type.

 

[ELA]

here is a link showing extension wire and colors:
http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=TC_GEN_SPECS_REF
As the others have said you must use the correct extension wire for the thermocouple type you are using. If you mix wire types you create new junctions that cause errors in the temperature reading value.

 

[realolman]

What type of wire is supposed to be run between a thermocouple and a transmitter? I believe its three wires, but is there a particular size or type that is standard? Will a regular #16 or #18 shielded triad be sufficient?

Is it general practice not to use fork lugs when connecting these wires? Any problems with doing so?

Every body else pretty much covered it, but because you mentioned three wires, I will add that there are only two wires that actually do anything. The thermocouple actually generates a small voltage, based on the amount of heat applied to it, the two different metals touching each other, , and the type of thermocouple.

The third wire may be a shield connection, beacuse the voltages you are dealing with are pretty small. You don't want any strays getting involved. Sometimes the thermocouple is grounded to the probe case. Sometimes, you can't ground them, depending on your amplifier.

 

[KentAT]

Since you mentioned three wires, are you sure your device is a thermocouple? I only ask because there are 3-wire RTDs for measuring temperature, having 1 white + 2 reds, or vice versa.

Can't say I've ever run into a 3-wire TC.

Kent

 

[GeorgeB]

Also you will notice the thermocouple extension wire contains a red and white wire. The white conductor terminates to the + terminals and the red to the -.
The extension cable comes both shielded and unshielded. I typically recommend the shielded type.

The extension cable is nominally the same alloys that the thermocouple is ... indeed, thermocouples, if high accuracy is not needed can be made with the extension cable. We used to twist and silver solder one, I don't remember if it was J or K, when our primary purpose was to have a good idea of temperature higher than thermistors would work.

 

[realolman]

Since you mentioned three wires, are you sure your device is a thermocouple? I only ask because there are 3-wire RTDs for measuring temperature, having 1 white + 2 reds, or vice versa.

Can't say I've ever run into a 3-wire TC.

Kent

Good thought... could be some other sort of a temperature sensor also ....like an LM 34 or something