The temperature display of the vacuum heat treatment electric furnace used in the experiment is incorrect

The incorrect temperature display of the vacuum heat treatment electric furnace used in the experiment may be caused by various factors such as thermocouple failure, temperature controller error, circuit interference, or vacuum environment influence. The problem needs to be solved through systematic troubleshooting and targeted repair. The following is a specific analysis of the reasons and solutions:

1. Thermocouple related issues
Thermocouples are the core components for temperature measurement, and their failure or improper installation can directly lead to temperature display deviations.
Damaged or aged thermocouple
Phenomenon: The temperature display fluctuates greatly, there is no reading, or the displayed value is far lower than the actual temperature.
reason:
Thermocouple wire breakage (such as long-term high temperature causing molybdenum wire to become brittle).
Damaged insulation layer leads to short circuit (such as cracking of alumina ceramic tube).
Carbon deposition or oxidation on the thermocouple head (especially prone to occur in carbon potential control experiments).
Solution:
Visual inspection: Observe whether the thermocouple wire is broken and whether the insulation layer is intact.
Resistance test: Use a multimeter to measure the cold end resistance of the thermocouple. If the resistance value is infinitely large (open circuit) or far below the standard value (short circuit), it needs to be replaced.
Replacement steps:
Turn off the power and wait for the furnace temperature to drop to room temperature.
Loosen the fixing screw of the thermocouple and slowly remove the old thermocouple.
Insert a new thermocouple (ensuring that the insertion depth is consistent with the original position) and fix it with high-temperature ceramic fiber.
Re calibrate the temperature controller (see “Temperature Controller Calibration” below).
Deviation of thermocouple installation position
Phenomenon: There is a fixed deviation between the displayed temperature value and the actual furnace temperature (such as the displayed value being 50 ℃ lower than the actual).
reason:
The thermocouple is not inserted into the central area of the furnace and is affected by local hot and cold spots.
The thermocouple protective sleeve (such as alumina tube) is too long, causing temperature measurement delay.
Solution:
Repositioning: Insert the thermocouple into the geometric center of the furnace, ensuring that the temperature measurement point is located near the workpiece.
Shorten the protective tube: If the protective tube is too long, it can be shortened to 5-10mm (sufficient length should be reserved to prevent the thermocouple wire from directly contacting the workpiece).

2. Temperature controller error
The temperature controller is the center of temperature display and control, and incorrect parameter settings or hardware failures can cause abnormal display.
Temperature controller parameter setting error
Phenomenon: The deviation between the temperature display value and the standard thermocouple measurement value is fixed (such as a display value that is 20 ℃ higher).
reason:
The temperature controller is not correctly matched with the thermocouple type (such as mistakenly setting the N-type thermocouple as the S-type).
The temperature compensation parameters (such as cold end compensation) have not been calibrated.
Solution:
Check the thermocouple type settings: Enter the temperature controller menu and confirm that the thermocouple type (such as N type, S type) is consistent with the actual one.
Cold end compensation calibration:
Insert a standard thermocouple (such as an S-type platinum rhodium thermocouple) into the furnace temperature measurement hole and connect it in parallel with the equipment’s built-in thermocouple.
Record the readings of both, and if the deviation is greater than ± 1 ℃, adjust the cold end compensation parameters of the temperature controller (refer to the equipment manual for specific methods).
Restore factory settings: If the parameters are chaotic, you can try restoring the factory settings and recalibrating.
Hardware malfunction of temperature controller
Phenomenon: The temperature display value fluctuates randomly or jumps irregularly.
reason:
The ADC (Analog to Digital Converter) of the temperature controller is damaged.
The connection between the display screen and the motherboard is loose.
Solution:
Replacement test: Replace the original equipment with a spare temperature controller and observe whether the temperature display returns to normal.
Contact the manufacturer: If the temperature controller is confirmed to be faulty, it needs to be returned to the factory for repair or the motherboard needs to be replaced.

3. Line and interference issues
Electrical circuit faults or electromagnetic interference may cause abnormal transmission of temperature signals.
Loose or damaged wiring connections
Phenomenon: The temperature display value is unstable (such as suddenly jumping from 800 ℃ to 1200 ℃).
reason:
The thermocouple compensation wire is loosely connected to the temperature controller.
Damaged outer layer of the circuit leads to short circuit or poor grounding.
Solution:
Tighten connection: Check the connection screws between the thermocouple compensation wire and the temperature controller/thermocouple to ensure good contact.
Replace the circuit: If the outer skin of the circuit is damaged, it needs to be replaced with a high-temperature resistant silicone cable (temperature resistance ≥ 200 ℃) and insulated properly.
electromagnetic interference
Phenomenon: Temperature display value experiences spike interference when the device is started or turned off.
reason:
Electromagnetic interference is generated by nearby high-power equipment such as frequency converters and welding machines.
Poor grounding of temperature controller.
Solution:
Shielding treatment: Wrap the thermocouple compensation wire with a metal shielding cover and ensure reliable grounding.
Stay away from interference sources: Keep the distance between the electric furnace and high-power equipment at least 1 meter.
Optimize grounding: Ensure that the temperature controller, electric furnace casing, and compensation wire shielding layer are grounded together, with a grounding resistance of less than 4 Ω.

4. Impact of vacuum environment
In a vacuum environment, the weakening of heat conduction and convection may lead to temperature hysteresis or local temperature differences.
Temperature measurement lag
Phenomenon: The temperature display value rises slowly and there is a time difference between it and the actual furnace temperature (such as the displayed value during the heating stage being 100 ℃ lower than the actual value).
reason:
Thermocouple protective sleeves have low thermal conductivity (such as aluminum oxide tubes).
The vacuum degree inside the furnace is too high (<10 ⁻ ³ Pa), and the heat radiation conduction efficiency decreases.
Solution:
Replace protective tube: Use materials with higher thermal conductivity (such as molybdenum tube, graphite tube), but consider corrosion resistance.
Optimize temperature measurement points: Insert thermocouples into the interior or near the surface of the workpiece to reduce temperature measurement hysteresis.
Local temperature difference
Phenomenon: There is a large temperature difference at different positions inside the furnace (such as the top being 50 ℃ higher than the bottom), resulting in a discrepancy between the displayed value and the actual workpiece temperature.
reason:
Uneven distribution of heating elements (such as high power of a single-sided heating rod).
The airflow inside the furnace is not smooth (if a circulating fan is not installed).
Solution:
Adjust heating power: redistribute heating rod power through a temperature controller to make the furnace temperature uniform.
Install a circulating fan: Install a high-temperature resistant fan (such as a graphite fan) in the furnace to promote heat convection.

5. System troubleshooting and repair process
Preliminary inspection:
Confirm whether the electric furnace is in normal working condition (such as meeting the standards for vacuum degree and cooling water flow).
Check if the temperature display is only abnormal under specific operating conditions (such as high temperature section, vacuum section).
Replacement test:
Replace the original thermocouple with a standard thermocouple and observe if the temperature display returns to normal.
Replace the compensation wire or temperature controller to troubleshoot the circuit.
Calibration and adjustment:
Calibrate the parameters of thermocouples and temperature controllers using the above method.
Adjust the heating power distribution or temperature measurement point position.
Recording and analysis:
Record temperature deviation data (such as time temperature curve) and analyze the deviation pattern.
If the problem persists, contact the equipment manufacturer or professional maintenance personnel for in-depth inspection.