A steel cone is heated by a nichrome ribbon to 45–50 °C. I placed a Type K thermocouple over the surface of the metal to measure the heat transferred over the metal surface. The thermocouple reads about 45 to 50 °C, which is expected. The issue is when I put a plastic cap (enclosure) over the metal cone, the temperature drastically decreases.
There is a metal cone made of mild steel.
A nichrome ribbon wire of 0.09 mm thickness is glued as a vertical strip from the tip to bottom on the metal surface of cone.
On the opposite side of the metal surface a beaded thermocouple wire of 40 awg (0.08 mm) is glued from the tip to bottom.
Both of them are placed on the metal using a superglue.
A plastic cap that has a similar cone shape is put to the metal. The air gap between the metal and the plastic structure is 0.1 mm. In this gap the Nichrome wire and a Type K thermocouple are placed.
The structure is:
plastic cap ->Thermocouple(or Nichrome wire)->glue(Superglue or Loctite)->Metal surface.
Without the plastic cap, the thermocouple measures about 45 °C after 4 to 5 minutes of heating.
When the plastic cap is added, the temperature increases up to 40 °C and struggles to reach 45 °C. The approximate time it takes to reach 45 °C is 10 to 12 minutes.
How is it possible to ensure that the thermocouple is measuring the temperature of the metal and not of the plastic?
We do not want the temperature measurement to change when the plastic cap is inserted. Is there any quick way of heating the plastic side and also getting the right temperature measurement?
I am open to any suggestions to improve this topology.