Accurate melt temperature
Vol. 17 #2, July 1990
When accurate melt temperature data is required from a melt stream thermocouple, use a variable depth probe.
If you want to monitor the average melt stream temperature in a circular pipe, rather than a random point of the temperature profile, place the thermocouple tip at a depth of 1/3 the diameter of the pipe. This temperature gives a usable estimate of the mixing cup temperature of the melt stream.
This checked well for PET and was reported good for polyolefins by experienced coworkers. This is easily checked for your system by plotting both temperatures.
See also
Melt temperature
Melt thermocouples
Temperature control