What is the crosstalk to the sensor caused by heater leakage in a hot runner?

I. Core Mechanism of Crosstalk Generation Leakage Current Path Coupling: After the heater insulation is damaged, 220V high voltage leaks through the damaged insulation layer to the metal nozzle/runner body, and then directly into the millivolt-level weak signal circuit of the K-type thermocouple through the tiny distributed capacitance between the sensor probe and the metal housing, and the insulation gap. Common Mode Voltage Rise: Leakage will generate a common mode voltage of tens to hundreds of volts at the sensor signal terminal to ground, far exceeding the common mode rejection capability of ordinary temperature controllers, directly causing insufficient CMRR, resulting in temperature data jumps. Ground Loop Amplification Interference: The leakage current will form an additional ground loop current between the hot runner metal housing and the equipment ground, further superimposed on the sensor signal link, amplifying the crosstalk intensity. II. Typical Characteristics of Crosstalk The temperature reading displayed by the temperature controller jumps irregularly; even when the actual nozzle temperature is stable, the measured temperature value suddenly fluctuates by tens of degrees Celsius. At the moment the heater starts, the sensor temperature readings show a significant jump. After the heater stops heating, this jump weakens or disappears. Measuring the voltage to ground at the sensor signal terminal with a multimeter reveals an AC leakage voltage of tens of volts, far exceeding the millivolt level signal voltage under normal operating conditions. III. Targeted Solutions Emergency Isolation of Leakage Source: Immediately stop using the poorly insulated heater. Use a megohmmeter to test the heater's insulation resistance. If the insulation resistance is below 0.5MΩ, replace the damaged heater directly, cutting off the leakage path at its source. Signal Link Shielding Optimization: Replace ordinary thermocouples with double-shielded, common-mode interference-resistant PTFE insulated wires. Ensure the shielding layer is reliably grounded at one end to prevent the leakage electric field from directly coupling to the signal core wire. Breaking the Grounding Loop: Add a high-temperature resistant alumina insulating bushing between the heater and the metal flow channel. This prevents leakage current from entering the sensor circuit through the flow channel housing, completely cutting off the crosstalk path of the ground loop. Improve the temperature controller's immunity: Replace with a Husky series temperature control module with one boasting high CMRR (≥120dB), significantly enhancing its ability to suppress leakage common-mode voltage and preventing temperature measurement runaway caused by crosstalk.