Open circuit and short circuit are the two most obvious sudden faults of hot runner thermocouples, which will directly trigger the alarm of the temperature controller and stop the heating of the hot runner zone, and accurate judgment and rapid processing are essential for reducing production downtime. Thermocouple open circuit fault is manifested as the controller displaying abnormal symbols or infinite temperature, which means the internal thermoelectric wire is broken or the wiring terminal is disconnected. The common occurrence positions include mold wiring bending section, nozzle internal temperature measuring probe root and connector pin welding position, mostly caused by excessive bending, pulling and long-term thermal fatigue fracture.
Short circuit fault is manifested as temperature display disorder, instantaneous temperature jump or controller power-off protection. It is caused by the contact and conduction of positive and negative thermoelectric wires. The main reasons are damage of the thermocouple insulation layer by high temperature ablation, melt leakage wrapping the probe and wiring, and moisture condensation in the mold leading to electrical conduction between wires. On-site maintenance can use a multimeter to measure resistance value to quickly distinguish fault types: infinite resistance is open circuit, near zero resistance abnormal conduction is short circuit.
When dealing with open circuit faults, first check the external connector and wiring harness for breakage, cut off the damaged section and re-crimp and wire; if the probe inside the nozzle or manifold is broken, it needs to be disassembled and replaced with a matched new thermocouple, and strictly control the insertion depth and fixing tightness during installation. For short circuit faults, it is necessary to first cut off the power supply to check the insulation layer damage position, replace the high-temperature insulation wiring harness, clean the melt residue and moisture in the installation hole, and re-layout the wiring to avoid contact with metal mold plates and high-temperature heating rings. After troubleshooting, it is necessary to conduct temperature rise test and real-time monitoring to ensure that the signal is stable and there is no repeated fault.
