Workshop ambient temperature changes significantly with seasons, ranging from 10–20℃ in winter to 30–40℃ in summer, which disturbs cold junction compensation baseline and generates persistent thermocouple reading deviation if without targeted calibration measures. The Seebeck effect of thermocouples calculates actual hot zone temperature based on the temperature difference between the hot sensing junction (nozzle/manifold) and cold junction (controller wiring terminals). Seasonal temperature swing directly changes the cold junction's reference temperature, forming measurement errors of 6–15℃ on uncalibrated hot runner systems.
In low-temperature winter workshops, the controller terminal block cold junction temperature drops sharply. The built-in cold junction sensor outputs low reference data, making the controller calculate a higher hot runner temperature than reality. Misled by false high readings, the system reduces heater power output, leading to insufficient melt temperature, cold slugs, incomplete filling and obvious weld lines on plastic parts. For thin-wall electronic molds with narrow flow channels, insufficient temperature seriously reduces melt fluidity, drastically increasing the short-shot reject rate.
High-temperature summer workshops create the opposite deviation: the cold junction ambient temperature rises, the controller misjudges the hot runner zone as lower than the set value, and continuously increases heating power to compensate. Long-term overheating causes plastic material carbonization, gate drooling and stringing defects. For high-temperature PEEK and PPS molding, excess heat leads to polymer thermal decomposition, releasing toxic volatile gas and producing brittle, discolored products. High ambient temperature also accelerates aging of thermocouple wire insulation and connector plastic shells, shortening the service life of temperature measurement accessories.
Workshop temperature fluctuation between day and night amplifies seasonal drift further. Factories running single-shift production shut down heating equipment overnight in winter; the controller terminal block cools to near 10℃, while the next morning workshop temperature rises rapidly after equipment startup, forming dynamic cold junction offset that cannot be eliminated by one-time static calibration. Multi-shift 24-hour continuous production lines have smaller day-night temperature gaps, but seasonal overall temperature shift still requires regular calibration adjustment.
Three standardized countermeasures eliminate seasonal temperature interference. First, perform cold junction recalibration at the start of summer and winter every year, using a certified portable thermometer to collect real ambient temperature at controller terminals and input the reference value into the controller compensation menu. Second, install constant-temperature air conditioning for the controller electrical cabinet, maintaining internal cabinet temperature stably at 22–26℃ all year round to isolate seasonal workshop temperature impact on cold junction sensors. Third, adopt intelligent digital thermocouples with built-in automatic cold junction compensation chips, which dynamically correct signal offset in real time as ambient temperature changes, reducing seasonal reading deviation to below ±0.5℃ without frequent manual calibration.
Daily pre-production temperature check also helps discover seasonal drift early. Operators record the room-temperature thermocouple reading before heating the mold; if the displayed value deviates more than 3℃ from actual ambient temperature, immediate calibration is required. Timely handling of seasonal temperature disturbance stabilizes thermocouple measurement accuracy all year round, avoids batch defective products caused by seasonal baseline offset, and maintains consistent molding quality of hot runner molds in different seasons.
