Field calibration verification is essential for ensuring hot runner process stability. Using a temperature simulator-a device that generates a precise millivolt signal to simulate a thermocouple output-allows quick and accurate verification of the controller input and measurement accuracy without removing the sensor from the mold.
What a Simulator Does. A thermocouple simulator generates a precise DC voltage that corresponds to a specific temperature for a given thermocouple type. For example, it can output 11.29 mV to simulate a Type K thermocouple at 280°C. When connected to the controller input in place of the sensor, it verifies whether the controller reads the correct temperature.
Isolating the Fault. The simulator test answers a critical question: is the problem in the sensor/wiring or in the controller? Connect the simulator directly to the controller input. If the controller reads accurately, the controller and its cold-junction compensation are working-the fault lies in the sensor or wiring. If the reading is inaccurate, the controller input module requires service.
Step-by-Step Procedure. (1) Disconnect the thermocouple from the controller. (2) Connect the simulator leads to the controller input, matching polarity. (3) Set the simulator to the desired temperature (e.g., 280°C for typical molding). (4) Wait 30 seconds for the controller to stabilize. (5) Read the controller display-it should match the simulator setting within the controller's accuracy (typically ±0.5°C). (6) Repeat at 200°C and 350°C to verify linearity.
Interpreting Results. If the controller reading matches the simulator within specification, the controller and cold-junction compensation are functioning correctly. Proceed to check the sensor resistance and wiring. If the controller shows a significant error, the input module or cold-junction sensor may be faulty-contact the controller manufacturer for repair or replacement.
Using an Ice Point Reference. For more precise verification, use a simulator in combination with an ice point reference (0°C). This tests the controller's cold-junction compensation directly. Connect the simulator through the ice point, set the simulator to 0°C, and verify the controller reads 0°C. This confirms the cold-junction sensor is accurate.
Documentation. Record simulator test results in the maintenance log. This data supports quality audits and provides a baseline for future troubleshooting. Regular simulator testing (quarterly) helps detect controller drift before it affects production.
