Why Thermocouple Polarity Reversal Causes Hot Runner Heating Abnormity

One of the most common wiring errors for hot runner thermocouples is a polarity connection problem. Reversed positive and negative poles will immediately cause a number of unusual heating phenomena, which can easily confuse on-site debugging staff. Different poles provide opposing thermoelectric signals in the same temperature environment, and all conventional K-type hot runner thermocouples have fixed polarity distinction.

The temperature controller receives voltage feedback signals that are entirely reversed following polarity reversal. Serious overheating inside manifolds and nozzles results from the system's false judgment that the temperature is continuously dropping when the actual hot runner temperature is rising. This causes the system to continuously output heating power blindly. A temperature that is too high may quickly break down and carbonize plastic melt, resulting in a large number of damaged goods.

Conversely, a reversed signal causes the controller to misunderstand high temperatures and instantly stop heating when the real temperature drops. This leads to inadequate melt temperature, poor fluidity, and a variety of molding flaws like short shots and weld lines. In severe situations, the temperature controller's internal program logic will become disorganized due to repeated incorrect signal feedback, which will result in the constant temperature locking function failing.

Long-term use of reversed polarity will also harm the initial steady thermoelectric conversion performance, hasten thermocouple core wire aging and performance attenuation, and even result in irreversible sensing element failure. In order to completely eliminate hidden issues caused by polarity reversal, operators must strictly distinguish wire colors and marking symbols during wiring, verify standard polarity access prior to power-on testing, and formally perform low-temperature trial heating verification following wiring completion.