Correct Use Methods of Thermocouple Cold Junction Temperature Compensation Technology

The primary auxiliary technology used to guaranty the precise temperature measurement of hot runner thermocouples over extended distances is cold junction temperature compensation. The temperature differential between the hot and cold ends has a direct impact on the thermoelectric potential produced by thermocouples. In actual production, it is not always possible to maintain the cold end connected to the temperature control terminal at the standard zero-degree reference temperature. As a result, the temperature of the cold end will constantly fluctuate due to changes in the workshop ambient temperature, which will lead to systematic errors in the temperature measurement data. Such reference temperature mistakes can be efficiently eliminated and the detected temperature data can be made infinitely close to the actual operating temperature through the scientific and standardized application of cold junction compensation technology.

Currently, the temperature controller's automatic cold junction compensation feature is the most popular in the injection molding sector. The temperature control box in this mode has a high-sensitivity ambient temperature sensing element that can track the temperature of the cold junction connection site in real time. In order to correct the deviation data and achieve automatic error correction without requiring technicians to make repeated manual adjustments, the system automatically computes the temperature error value produced by the reference temperature deviation based on the detected actual cold junction temperature value. It then superimposes the compensation value on the original temperature feedback signal. The majority of traditional hot runner manufacturing equipment with stable wiring arrangement may use this compensation approach, which has the benefits of straightforward operation, real-time response, and robust follow-up performance.

The temperature control box must first be installed in a sensible location to guaranty that the automatic compensation mechanism fully operates during actual use. In order to prevent local overheating of the cold junction caused by direct baking of high-temperature heat flow, as well as direct blowing of cold air from workshop air conditioners and fans, which can cause a sudden drop in the temperature of the cold junction and an unstable compensation benchmark, the temperature control equipment must be placed in a cool, ventilated position away from high-temperature heat sources like hot runners and heating furnaces. In order for the built-in temperature sensor element to accurately record the actual cold junction temperature and guaranty the correctness of automated compensation data, maintain a somewhat constant ambient temperature around the terminal box.

Another crucial component in ensuring the impact of cold junction compensation is the standard matching of compensation wires. In order to extend the cold end from the high-temperature mold side to the stable temperature control box side and counteract the temperature error produced in the extension section, special thermocouple compensation wires have the same thermoelectric property trend as the internal wire core of thermocouples. It is strictly prohibited to utilize non-matched versions of compensation wires or regular high-temperature wires throughout the wiring and replacement operation. In order to prevent compensation failure and increase temperature measurement deviation, different types of thermocouples must be matched with matching special compensation wires. Additionally, it is important to make sure that the positive and negative pole wiring is consistent and that the wire specifications are unified.

Manual fixed value compensation mode must be used for some antiquated temperature control equipment that lacks an automatic compensation capability. Manually adjust the controller's cold junction compensation setting based on the production workshop's average ambient temperature throughout the year. In order to keep the temperature measurement error within the qualified range, the compensation parameter value should be appropriately lowered in the winter when the temperature is low and raised in the summer when it is high. Regularly compare and calibrate the actual temperature to make timely adjustments to the compensation parameters.

Make sure the cold junction compensation system operates steadily for a long time, keep the terminal connection tight and clean, remove dust and oxide rust from the contact points, and regularly check and maintain the cold junction connection position in daily work. The inherent measurement accuracy of thermocouples can be maximized, systematic temperature errors can be eliminated at the technical level, and more accurate and dependable temperature data support for refined injection molding process production can be provided by mastering the proper use rules of cold junction compensation technology.