Step 1: Quickly check for basic wiring and hardware concerns.
First, ensure that the thermocouple compensating wires are not inverted, that the terminals are free of oxidation and weak connections, and that the compensating wires' insulation is not damaged or leaky. Remove reading discrepancies caused by basic wiring faults.
Measure the thermocouple circuit resistance using a multimeter and confirm it falls within the typical range of 5-50Ω. Examine the thermocouple armour wires for hidden breakage and insulation damage, thereby reducing hardware deterioration issues.
Verify the thermocouple calibration setting in the Husky temperature controller to ensure it properly matches the actual thermocouple, with no consistent reading deviations caused by parameter incompatibilities.
Step 2: Check for installation and environmental interference issues.
Check the depth of the thermocouple insertion into the hot runner, ensuring that the sensor end is totally in contact with the temperature measurement site, with no probe suspension or failure to contact the runner wall, resulting in thermal conductivity problems. Such issues can cause variances of up to 8℃.
First, look at on-site electromagnetic interference, ensuring that power connections for high-power equipment like frequency converters and servo motors are routed separately from thermocouple signal lines. To prevent power frequency interference, ground the temperature controller signal shield to a resistance of ≤4Ω. This will remove 0.5~2℃ variations in readings.
Inspect the thermocouple protection tubes for wear and cracks to avoid moisture entry, which could lead to insulation deterioration and parasitic potential, resulting in reading deviations.
The third stage is to calibrate the parameters and rectify the system depth. Repeat multi-point calibration, carrying out comparative testing at three separate temperature points (20%, 50%, and 80% of the range). Create a linear compensation curve by recording error values at each step. This eliminates nonlinear temperature measurement errors from thermocouples.
Check the temperature controller's cold junction compensation parameters to ensure that the cold junction temperature reference value is totally consistent with the observed ambient temperature at the wire location, thereby correcting system faults caused by cold junction compensation drift.
Replace the temperature controller signal isolator to remove aberrant signal drift caused by isolator failure, then restart the PID self-tuning software to optimise the temperature control curve.
Final closed loop verification: After rectification, the system was operated at a steady temperature for two hours. Temperature data was collected and compared during the process using a conventional thermocouple. Confirmed reading variation was ≤±1℃, temperature fluctuation was ≤±1℃, and no drift or leaps occurred. This entirely corrected the issue of inaccurate readings upon calibration.
This tiered troubleshooting procedure may resolve 99% of problem occurrences involving faulty thermocouple readings after calibration, eliminating unnecessary disassembly and production line delay.
