Thermocouples measure your temperature inside your kiln. When you see the digital readout on the front of your kiln even if your kiln is not firing there is still a noted inside temperature. At times the thermocouple can get a carbon coated on the tip end. You can take a brass brush and clean it. Over time with a lot of enamel firings it will not read correctly. This depends on your activity. I have seen them last 2-5 years. But I my say if you are ever in doubt your kilns is not keeping the correct temperature replace this compounite first.
These thermocouples are different sizes. Let me know your kiln model.
Happy Enameling Patsy