THERMOCOUPLE INFORMATION

 A thermocouple is a device that is used to sense temperature in your  process.  It has two wires that are made of different metals they are  Joined together at one end. In the Type J thermocouple one wire (or leg)  is made of Iron, the other wire is made of Constantan. You may hear of  the refered to as "an Iron Constantan thermocouple" or just Type J.
 

There are several types of thermocouples used to sense temperature, but  for our purpose, we will concentrate on the most common thermocouple  type in the plastics market in the United States... the Type J.
 

Type J thermocouples are used in Extrusion, Blow Molding and Injection  Molding. They are used because of the relatively low cost and acceptable  accuracy in the 0-1600 deg. F temperature range.
 

When the thermocouple is connected to a temperature controller, it  enables the temperature controller to measure the process temperature.
 

HOW DOES A THERMOCOUPLE WORK:
 

This is the short version of how a thermocouple works.  As we know, a  thermocouple is made up of two different metals, then joined at one end,  this forms the hot junction, sometimes referred to as "the hot end".
 

When the temperature changes (increases for example) a small dc voltages  is produced in proportion to the temperature because of the two  dissimilar metals. If both wires were Iron or Constantan, there would  not be a voltage produced, so you would not have a thermocouple.