How to Determine if a Hot Runner Temperature Sensor is Failed?

To find out if a hot runner temperature sensor has failed, you need to look at its output performance, system feedback, and actual tests. Unusual temperature readings, alerts from the control system, or less stable processes are the most direct signs. Here are some specific steps and strategies for assessment:

I. Check the performance of the sensor output


When a sensor fails, it usually shows up in the following ways:

Fixed Temperature Reading: The sensor output value stays the same even when the temperature fluctuates, which means that the sensing element may be broken or the circuit may be open.

Severe Fluctuations or Jumps in Reading: If the data on the screen changes a lot and in strange ways (for example, if it goes up or down more than ±10℃), it could mean that the internal contact is bad, the insulation is broken, or there is a lot of electromagnetic interference.

No Signal Output at All: The temperature controller shows "open" or "---," which means that the sensor circuit is broken or the internal probe is broken.

If the difference between the measured value and the actual temperature is more than ±5℃ and other factors have been ruled out, the sensor is not accurate. This is based on a standard thermometer.

II. Looking at the feedback from the control system

Most of the time, hot runner temperature management systems can check themselves. You can use the following strategies to help in diagnosis:

If you see fault codes like "sensor error," "open circuit," or "short circuit," it means there is an issue with the sensor or wiring.

Read Equipment Fault Codes (for Integrated Systems): Use a diagnostic tool to look at the data stream. If you get messages like "Temperature sensor signal too high/too low" or "Response timeout," verify the status of the sensor.

Watch for Unusual Heating Behavior: If the sensor fails, the temperature controller may not be able to accurately read the temperature, which could cause the heating to continue (overheating) or stop (low temperature). This could cause the product to shrink, flash, or carbonize.

III. Testing of the Body and the Electricity

1. Look at it

Look for signs of bending, corrosion, or burning on the probe.

Look for signs of water getting in, oxidation, or looseness in the connector.

Look for damage, dents, or cracks that have gotten worse over time on the cable.

2. Measuring Resistance (Works with PT100 and NTC Thermistors)

Use a multimeter to check the resistance at room temperature:

At 20°C, the PT100 has a resistance of about 109.7Ω, and it goes up by about 0.385Ω for every 1°C increase.

NTC thermistors have a resistance that goes down as the temperature goes up. Different models have different specifications (for example, a 50K NTC has a resistance of 50kΩ at 25°C).

Put the sensor in hot water or another hot place and see if the resistance changes as it should. Failure means no change.

3. Testing Voltage (for Thermocouples)

While the device is on, check the output voltage.

K-type thermocouples make about 4.1mV for every 100 degrees Celsius. A steady or zero voltage means that something is wrong.

4. Insulation Resistance Test: Use a megohmmeter to see how well the insulation between the sensor housing and the signal line works. The usual value should be more than 20 MΩ. A reading lower than this may mean that there is a leak or moisture, which could make the test less accurate.

IV. Method for Checking Replacement (Final Confirmation)

If the previous tests make you unsure, the best way to find out for sure is to replace the sensor with a new one of the same model and test it again:

The original sensor has failed if the temperature display goes back to normal and the heating control is stable following the replacement.

Check the wiring terminals, temperature controller, or power module if the problem keeps happening.