Every hot runner thermocouple comes with a standard internal resistance range determined by alloy wire diameter, overall length and internal structural design. Matching resistance value is not merely a technical parameter, but a fundamental prerequisite for stable temperature sensing and normal controller recognition. When the actual resistance deviates beyond the standard range, the temperature controller misjudges internal circuit conditions, produces distorted temperature readings, and triggers false alarms of open circuit or short circuit even if the thermocouple structure remains intact.
Excessively high resistance usually stems from overly thin alloy wire, overly long customized probe length, or hidden micro fracture inside the wire caused by bending fatigue. The controller receives weakened thermoelectric signals, resulting in displayed temperature much lower than actual working temperature. The heating coil keeps outputting excessive power, leading to nozzle overheating, material carbonization, gate drooling and continuous wire drawing defects. On the contrary, abnormally low resistance is caused by insulation layer damage, internal wire lapping or sheath moisture penetration, which induces signal short circuit, instantaneous temperature jump and random fluctuation, breaking the thermal balance of the entire hot runner zone.
In daily mold maintenance, using a multimeter to measure resistance before installation can quickly screen unqualified thermocouples, avoid installing defective products into the mold, and prevent unnecessary mold disassembly and debugging losses. For customized ultra-long or right-angle bent thermocouples, strictly following factory standard resistance tolerance can ensure compatibility with mainstream hot runner controllers, maintain accurate closed-loop temperature regulation, and avoid hidden quality risks caused by resistance mismatch.
