Replacing a damaged reduced-bore thermocouple requires four steps: safety isolation, removal of the old probe, installation of the new probe, and functional verification. This ensures operational safety and measurement accuracy.
1. Safety Preparation and System Isolation
Power Off and Depressurize: Turn off the power to the temperature measurement circuit and release pressure in the hot runner or pipeline to prevent high-temperature media from spraying out.
Mark Polarity: Clearly label the positive (+) and negative (−) leads to avoid reverse connection and temperature misreading.
Wear Protective Equipment: Wear high-temperature resistant gloves and goggles to prevent burns or foreign object splashes.
2. Removing the Damaged Thermocouple
Loosen the Fixing Part: Use a suitable wrench to remove the nut or retainer between the protective tube and the mounting base.
Smoothly Pull Out: Slowly pull out the old probe along the axis, avoiding violent shaking that could damage the mounting hole.
Clean the Mounting Hole: Remove carbon deposits, oxide scale, or sealing residue to ensure smooth insertion of the new probe.
If the probe is stuck, gently rotate it and use a special puller; do not force it by striking it.
3. Install the new thermocouple
Check parameters: Confirm that the new probe's graduation number, outer diameter, length, and insertion depth are consistent with the original design;
Apply lubricant: Lightly apply molybdenum disulfide high-temperature grease to the surface of the protective tube to prevent jamming;
Insert completely: Insert the probe fully to the specified depth (usually 5–10 mm beyond the centerline);
Tighten the seal: Retighten the nut or ferrule. It is recommended to use a torque wrench to control the preload and avoid overtightening the probe.
4. Functional Verification and Commissioning
Pre-Power-On Testing:
Test continuity with a multimeter (resistance 1–100Ω);
Measure insulation resistance with a 500V megohmmeter (≥100 MΩ, high-end applications require ≥1000 MΩ);
Cold Junction Compensation Setting: Confirm the cold junction temperature compensation parameters are correct in the control system;
Heating Observation: Gradually heat to the operating temperature and observe whether the temperature curve is stable and without jumps;
PID Fine-Tuning: Optimize control parameters based on the response to improve system stability.
Recommendation: Record the new probe serial number, replacement date, and initial reading for easy traceability management.
