How Low Ambient Temperature Affects Hot Runner Thermocouple Cold Junction

In winter and low-temperature manufacturing workshops, the ambient temperature will drop abruptly, which will adversely affect the cold junction temperature of hot runner thermocouples, thereby interfering with the cold junction compensation accuracy. Many moulders are unaware that the cold junction potential variation caused by the low ambient temperature may result in false high temperature feedback and anomalous hot runner thermal balance, and the set temperature is blindly adjusted when the winter quality shifts.

The cold junction of the thermocouple is located at the terminal of the temperature control cabinet, and is immediately exposed to the low temperature of the workshop. For example, fast drop of ambient temperature results in the lowering of cold junction temperature, the anomalous increase of the temperature difference between hot end and cold junction, and the increase of thermoelectric potential accordingly. Without high-precision automated correction, the temperature controller shows a number greater than the real runner temperature and hence wrongly reduces the heating power. The melt temperature and nozzle temp is not enough, the melt fluidity becomes bad, leading to shrinkage, weld lines and incomplete filling flaws.

The low ambient temperature will also cause the internal temperature of the temperature control cabinet to drop, impacting the operating state of the compensation module and electronic components, so that the compensation sensitivity and accuracy will be reduced. The temperature drift of each thermocouple channel is inconsistent, causing temperature imbalance between multi-zone manifolds and multi-cavity nozzles, and leading to unstable batch product quality.

The low temperature cold junction interference can be solved by putting the temperature control cabinet in a relatively stable temperature zone and avoiding the direct cold wind in winter. Provide thermal insulation and heating equipment for the terminal box to maintain the cold junction within a consistent ambient room temperature range. High-precision intelligent controller of thermocouple matching and improved cold junction compensation algorithm is used to automatically compensate low temperature variation. All thermocouples should be calibrated regularly at the turn of winter to minimise cold junction drift and keep the temperature control consistent all year long.