Our Kapton insulated thermocouples used in oven validation are fraying, the insulation is unwinding, and the copper wire is turning black. Are they defective?
No, this is a normal occurrence in Kapton insulated thermocouple wire used in high temperature depyrogenation applications. The fraying and unwinding of the insulation is caused by degradation of the fluorocarbon binder on the Kapton film wound on the wire. The higher the oven temperature, the more quickly this occurs. The black color on the copper wire is oxidation also caused by the high temperature found in the oven. And here also, the higher the oven temperature, the more quickly this occurs and progresses more deeply into the copper. This deep oxidation can affect wire uniformity and accuracy and will eventually cause loss of conductivity in the copper wire and failure of the thermocouple. Thermocouples should be replaced once unwinding begins as wire failure is not far behind.
September 23, 2009 at 4:29 pm | Uncategorized | No comment