Thermocouples measure temperature difference, not absolute temperature. The reference point, called the cold junction, is located at the controller terminal block. Changes in ambient factory temperature directly affect cold-junction voltage, creating measurement error unless compensated automatically.
Modern hot runner controllers include precision cold-junction compensation (CJC) sensors that continuously measure ambient temperature and adjust the thermocouple calculation accordingly. Low-cost or older controllers may use less accurate CJC, leading to consistent temperature offsets.
Long thermocouple cables increase sensitivity to ambient variation because more of the cable is exposed to factory conditions. Using high-stability, low-drift thermocouples reduces environmental influence.
In facilities with large temperature swings between day and night or summer and winter, poor CJC or low-quality thermocouples can cause noticeable shifts in part quality. Understanding this relationship allows operators to improve cable routing, reduce exposure, and select more stable components.
Ambient temperature influence is subtle but meaningful. For precision molding applications, controlling this variable through high-performance thermocouples and robust CJC is essential to maintaining all-shift, all-season stability.
