Thermocouple short circuit is a common electrical failure in hot runner temperature control system, which refers to the direct contact and conduction between the positive and negative wire cores inside the thermocouple or between the wire core and the outer protective sleeve. Once a short circuit fault occurs, the temperature controller will display abnormal temperature values such as ultra-high temperature or fixed low temperature, the heating system will be out of control, and even cause tripping power failure and burnout of temperature control modules in serious cases, which will seriously affect the safe and stable operation of production equipment. It is necessary to sort out common short circuit causes and master hierarchical troubleshooting methods to quickly eliminate faults and resume production.
The first common cause of short circuit is damage and aging of internal insulating structure. After long-term high-temperature baking, the high-temperature resistant insulating filler inside the thermocouple will gradually age, soften and collapse, losing the original isolation and fixing effect. The positive and negative alloy wire cores lose insulation protection and are easy to contact and overlap with each other to form an internal short circuit. In addition, when the outer protective sleeve is severely corroded and worn to produce holes and cracks, the external high-temperature melt gas and conductive dust will penetrate into the interior, which will also cause conductive connection between the internal wire core and the outer sleeve, triggering short circuit failure. This kind of internal structural damage short circuit mostly occurs in aging thermocouples that have been used for a long time, and the fault concealment is strong and it is not easy to find in the early stage.
The second inducement is line insulation damage and external extrusion short circuit. In the process of mold opening, closing and maintenance, the thermocouple compensation wires are squeezed, scratched and pulled by sharp metal parts, resulting in damage and falling off of the external insulating skin. The exposed positive and negative wire cores are in contact with each other or touch the metal mold shell, forming an external short circuit loop. In the high-humidity production workshop, the moisture condensed on the surface of the wires will also form a conductive layer, leading to intermittent leakage and short circuit of the signal lines, resulting in unstable abnormal temperature display.
The third reason is wiring terminal pollution and conductive dirt short circuit. A large amount of carbon dust, metal powder and oily dirt will accumulate at the wiring terminals of the temperature control box for a long time. These dirt have certain electrical conductivity. When accumulated to a certain extent, they will connect the adjacent positive and negative wiring terminals, resulting in short circuit at the cold junction connection end, disordering signal transmission and causing temperature display abnormality. This kind of fault often occurs in production lines with poor on-site sanitation conditions and serious dust pollution.
In view of different types of short circuit faults, targeted step-by-step troubleshooting measures should be adopted. Firstly, cut off the total power supply of the temperature control system to ensure safe operation, disconnect all thermocouple wiring terminals one by one, and separate the fault temperature zone lines for independent detection. Use a multimeter to measure the on-off resistance between the positive and negative poles of the thermocouple. If the resistance value is close to zero, it can be determined that a short circuit has occurred.
Secondly, distinguish internal short circuit and external line short circuit. Remove the compensation wire at the cold junction end and separately detect the resistance of the thermocouple body. If the body itself is short-circuited, it means that the internal insulation structure is damaged and cannot be repaired, and the whole thermocouple must be replaced directly. If the body is normal and the short circuit occurs in the external connecting lines, it is only necessary to find the damaged position of the wire, wrap and repair the insulation or replace the new compensation wire.
Finally, thoroughly clean the dirt and oxide layers on all wiring terminals, keep the terminal positions dry and clean, rearrange the wiring paths, avoid the signal lines being squeezed and scratched by hard objects, and add necessary insulation protection sleeves for the easily damaged line sections. After the fault is eliminated, conduct low-temperature trial heating test to confirm that the temperature display returns to normal and there is no repeated short circuit phenomenon, and then put it into formal production again.
In daily equipment management, regular inspection of the insulation state of thermocouple lines, timely cleaning of terminal dust and dirt, and avoidance of long-term over-temperature use can effectively reduce the occurrence probability of short circuit faults, maintain the safe and stable operation of hot runner temperature control electrical systems, and eliminate potential safety hazards in production.
