Grove high temperature thermocouple fail in strong EM field, why?

Was working on a project to measure the temperature inside an industrial grade electrical motor. Grove high temperature thermocouple seemed to be the ideal module to take on this task, however, when the motor span up the reading shown strong fluctuation between positive and negative reading and eventually the reading became incomprehensible. I know its probably caused by some kind of induction current from EM field, so does anyone know how to solve this problem or any kind of insulting materiel i should try out?

Hi there, do you only plug the sensor cable inside of the industrial grade electrical motor and leave the pcb board outside? thanks.

Seeed techsupport team