During the operation of the packaging machine, the thermocouple circuit, as the core unit of temperature monitoring, directly affects the heat sealing quality and equipment stability. Once abnormal phenomena such as signal distortion, temperature jump or continuous error occur, it is necessary to quickly locate the fault point and implement repairs. Based on common scenarios in the industry, this article sorts out the troubleshooting and optimization solutions for the thermocouple circuit problems of packaging machines.
Problem representation: Typical manifestations of thermocouple circuit abnormality
Temperature value drift: The temperature value on the display screen of the packaging machine is significantly different from the actual temperature of the heat sealing head, resulting in loose sealing or excessive melting.
Intermittent signal interruption: The "thermocouple disconnection" alarm is frequently triggered during equipment operation and needs to be restarted for recovery.
Local temperature distortion: In multiple sets of thermocouple lines of the same packaging machine, some channels have abnormal data, while the rest of the channels are normal.
Core cause analysis and response strategies
▌Cause 1: Line aging or mechanical damage
The thermocouple line of the packaging machine is in a high temperature and vibration environment for a long time, and the insulation layer is prone to brittleness and cracking, causing short circuit or grounding fault.
Solution:
Use a multimeter to measure the line resistance value in sections and lock the interval where the resistance increases abnormally or returns to zero.
When replacing damaged cables, high-temperature resistant silicone sheathed wires are preferred, and metal braided shielding tubes are installed in the 30cm section near the heat seal head.
Use spiral wiring for multi-bending active parts (such as robot arm joints) to avoid repeated bending and core breakage.
▌Cause 2: Electromagnetic signal interference
Electromagnetic noise generated by inverters, servo motors and other equipment around the packaging machine may be coupled to the thermocouple line, causing temperature signal distortion.
Solution:
Implement "twisted shielding + single-ended grounding" transformation for the thermocouple signal line, and the grounding point of the shield layer should be as close to the terminal block of the control cabinet as possible.
Connect an RC filter circuit in parallel at the signal input end to suppress high-frequency interference pulses.
Lay the thermocouple line and power cable in separate slots, and keep the minimum spacing distance above 15cm.
▌Cause 3: Failure of cold-end compensation
The temperature compensation circuit of the thermocouple reference end (cold end) is abnormal, resulting in a deviation in the temperature conversion reference value.
Solution:
Check the power supply voltage of the temperature compensation module in the control cabinet to ensure that it is stable within the rated value range.
Clean the oxide layer of the compensation terminal and use low-temperature solder to re-fix the virtual contact.
Regularly calibrate the cold-end compensation accuracy with a standard temperature source, and replace the compensation module when the deviation exceeds the threshold.
Preventive maintenance recommendations
Monthly inspection system: Check the appearance integrity of the thermocouple line of the packaging machine, test the insulation resistance and signal noise level.
Environmental adaptability optimization: Install insulated air ducts in high-temperature areas to reduce the risk of long-term heat exposure of cables.
Redundant backup design: Configure spare channels for thermocouple lines at key workstations to support one-click switching in case of failure.
Summary
Although the abnormality of the thermocouple line of the packaging machine may seem trivial, it may cause a chain of production accidents. Through systematic interference shielding, line protection and compensation calibration measures, enterprises can significantly reduce the risk of temperature out of control. It is recommended to incorporate the thermocouple system into the equipment preventive maintenance system, combine real-time monitoring data to predict fault trends, and ensure the continuous and efficient operation of the packaging machine.
