How to Determine if a Furnace Temperature Sensor is Damaged

Observing odd temperature readings, a delayed reaction, or no signal at all are the main indicators that a furnace temperature sensor is faulty. Verification of multi-point temperature measurements, historical curve analysis, and comparison with standard thermocouples are used for confirmation. Specific standards for judgment include the following:

 

1. Common Signs of Damage

The phenomenon

An explanation

Potential Repercussions

Absence of a Temperature Display or Variations

The control system shows "---," goes over its range, or exhibits abrupt value swings.

Sensor short circuit, open circuit, or inadequate contact

Slow Reaction to Temperature

During heating, the temperature increases far more slowly than the actual heating rate.

Carbon accumulation, aged thermocouples, or blocked protective tubes

Continuous Reading

Regardless of heating, the temperature value stays constant for a considerable amount of time.

Failure of a sensor or disruption of signal transmission

Deviation > 10°C from Other Measuring Points

Significant variation in the multi-point temperature measurement at a specific point

Damage to local sensors or improper installation

Warning Case: The H13 tempering furnace in a plant showed a temperature of 580°C, although the real temperature was only 550°C. Three batches of molds were destroyed because of inadequate hardness after an investigation showed that oxidation of the thermocouple connector resulted in unsatisfactory contact.

 

2. Rapid Testing Techniques on-site

Standard Thermocouple Comparison: Attach the original sensor in parallel with a standard thermocouple that has been validated by metrology. If the variance is greater than ±5°C after stabilization, it is deemed erroneous.

Initial Multimeter Testing: Determine whether the thermocouple output millivolt value is within a tolerable range by measuring it and comparing it with the calibration table (e.g., 580℃ equates to approximately 14.2mV for type K).

Mobile Temperature Measurement Verification: Take measurements at various locations within the furnace using a handheld thermocouple or portable infrared thermometer, then compare the results with the control system readings.

Practical Advice: To prevent interference from workpiece heat absorption, test in an empty furnace.

 

3. Managing and Avoiding Damage

Quick Disconnection and Replacement: As soon as damage is confirmed, replace the sensor and recalibrate the system.

Create Replacement Records: For traceability, note the model, serial number, operator, and replacement time.

Frequent Preventive Maintenance: Calibrate every quarter; reduce this to every six weeks when there is a large load.

Safety rules: "Investigate any abnormalities, verify the findings, and replace the faulty parts promptly." Together, these three ideas guaranty that the temperature measurement system is always dependable.