How to use a multimeter to test if a hot runner sensor is functioning correctly

Step 1: Get Ready and Follow Basic Safety Procedures

Turn off the machine and unplug the hot runner temperature control box. To prevent burns or electric shock, let the hot runner cool fully to room temperature.

Select 200Ω and set the multimeter to the resistance range (Ω range). To guaranty proper contact, clean the multimeter probes.

For testing, disconnect the sensor from the temperature control box and take out the sensor probe separately.

 

Step 2: Fundamental Testing Procedures and Outcome Evaluation

The following criteria are applicable for evaluating the K-type thermocouple sensor, which is the most widely employed in hot runner systems:

Normal Result Failure Judgment for the Test Item Operating Method

Test for Continuity and Basic Resistance

Make contact with each of the sensor's two pins using two multimeter probes.

The resistance reading should be between 2 and 20Ω at room temperature (25°C), which is within the typical range.

1. Resistance reading infinite (OL): This indicates a failure due to an open circuit, internal wire breakage, or loose connection.

2. A resistance value near 0Ω (<1Ω) indicates an internal short circuit in the sensor, a breakdown in the probe's insulation, and a failure.

Test of Insulation Performance

Attach one probe to the sensor pin and the other to the sensor's metal case or hot runner body.

Infinite resistance reading (OL): Normal insulation. A persistently low resistance value is a sign of sensor failure, leakage, and insulation degradation.

 

Step 3: Verification of Temperature (Optional, to further check sensitivity)

A quick temperature check can be carried out if the base resistance is normal but performance loss is still suspected:

Turn on the hot air pistol and blow it onto the sensor probe for three to five seconds while maintaining the multimeter connections (set the temperature to 100–150°C);

Watch the resistance change: As the temperature rises, a typical K-type thermocouple will exhibit a gradual and steady increase in resistance;

The probe sensitivity has deteriorated and failed if the resistance changes very little or not at all compared to a typical sensor.

Typical Safety Measures

Further testing is required to determine whether the temperature controller's irregularity is due to a malfunctioning temperature controller input module or loose wire terminals rather than an issue with the sensor itself if the test findings are normal;

The typical resistances of various sensor types (such PT100 RTDs) vary: A PT100's resistance at normal temperature is roughly 100Ω; this standard can be used to modify the judgment threshold.