Step 1: Quickly detect hidden flaws.
Check the thermocouple's insertion depth into the hot runner to ensure that the sensing end is entirely against the runner wall and that it fulfils ASME PTC 19.3 specifications. Eliminate "false temperature field" variations due to insufficient insertion depth.
Measure the body temperature of the cold junction compensation module with an infrared thermometer to ensure that the cold junction compensation parameters perfectly match the measured temperature, eliminating millivolt-level temperature measurement errors caused by cold junction temperature sensing deviations.
Check that the compensating wire index properly matches the thermocouple, ensuring that the positive and negative terminals are not reversed. Eliminate the problem of uncertain thermoelectric potential superposition produced by utilising conventional shielded wire instead of compensating wire.
Step 2: Make targeted parameter adjustments and corrections.
Use the Husky temperature controller's advanced calibration menu to execute piecewise linear calibration at three common temperature points: 200℃, 400℃, and 600℃. Enter measured error values for each location to create a new compensation curve that eliminates nonlinear deviations over the temperature range.
Perform PID self-tuning on the temperature controller to improve temperature control response characteristics and prevent calibration data drift caused by temperature oscillations.
Note: Keep the instrument offset adjustment range within ±50℃. Exceeding this range indicates a hardware flaw; do not forcefully modify parameters to hide the problem.
Step 3: Identify the mandatory replacement criteria.
If any of the following conditions occur, replace the thermocouple with a brand new one without further adjustment:
The divergence at many test points across the full temperature range after calibration is consistently > ±2.5℃, and parameter modifications still fail to converge to the permissible range.
The thermocouple cold junction resistance deviates from the initial value by >10%, and the room temperature insulation resistance is <100MΩ, indicating irreversible insulation degradation.
The thermocouple sensing contacts show oxidation spots and cracks, and the protective sheath is damaged and leaking; the cumulative service time has reached 80% of its lifespan.
If the same repaired thermocouple fails calibration more than 3 times within 12 months, and the cost of continuous calibration exceeds 40% of the price of a new thermocouple, immediate replacement is more economical.
This procedure can immediately resolve the issue of unqualified calibration after repair, taking into account both accuracy and maintenance cost control, and fully meeting the process requirements of Husky hot runner precision injection molding.
