Analysis and Solution for Injection Molding Machine Barrel Thermocouple Failure

Customer Issue Overview

A customer encountered an issue with temperature control malfunction on their Mirel 9118 controller for an injection molding machine and sent us the controller screen display.

From the display, we identified Error Code 030, which indicates a thermocouple disconnection error.

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Further examination of the controller display revealed that the temperature reading for the second section was abnormal, with an actual temperature significantly higher than the set temperature.

This suggests that the thermocouple in the second section may have failed, preventing the controller from accurately reading temperature data, which triggered the alarm.

Inspection and Troubleshooting Steps

1. Confirm Whether the Thermocouple is Faulty

Testing Method

  • Step 1: Use a multimeter to measure the thermocouple resistance.

Solution

  • If the thermocouple is confirmed to be faulty, replace it with a thermocouple of the same specifications.

  • After replacement, recalibrate the temperature control system and verify that the temperature readings return to normal.

2. Inspect Thermocouple Wiring Connections

Testing Method

  • Check whether the thermocouple terminal connections are loose, oxidized, or disconnected.

Solution

  • If loose connections are found, re-secure the terminal connections.

  • If the wiring is aged or damaged, it is recommended to replace it with high-temperature-resistant thermocouple wiring.

3. Test the main board of the controller Input Port

Testing Method

  • Short-circuit the second thermocouple’s I/O point on the mainboard to see if the issue persists.

  • If the alarm still occurs after short-circuiting, the issue is likely with the mainboard.

  • If the alarm disappears after short-circuiting, then the problem is not with the mainboard.

Solution

  • If the mainboard is confirmed to be faulty, it requires repair or replacement.

Through the above step, we identified that the root cause of the issue was a controller mainboard failure.

Preliminary analysis suggests that the thermocouple wiring might have accidentally come into contact with the heating wire, causing electrical current to transfer to the mainboard and overload it.

Temporary Emergency Solution

To keep production running on schedule while awaiting a permanent repair, we implemented a temporary workaround:

  • Step 1Reconnect the second thermocouple wire to the third thermocouple input port.

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Step 2Disable the temperature display for the second section on the controller to make the system ignore the faulty sensor.

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  • Step 3: Ensure that the equipment continues operating normally.

This approach allows the machine to keep running without replacing the mainboard immediately.

However, we strongly recommend repairing or replacing the damaged controller mainboard as soon as possible to ensure long-term system stability.

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