The inconsistency between the displayed temperature and the actual temperature of a tube furnace is a common problem, which may be caused by various factors such as thermocouples, temperature control systems, furnace structure, or operating methods. Now let's analyze in detail how to troubleshoot!

Commonly used vacuum atmosphere tube furnace (click on the picture to view product details)

1. Common causes and troubleshooting steps
Thermocouple issue
Phenomenon: Large temperature fluctuations, fixed deviations, or no response at all are displayed.
Troubleshooting:
Check the connection: Confirm that the thermocouple is firmly connected to the controller and compensation wire, without looseness or oxidation.
Calibration thermocouple: Use a standard temperature source (such as a calibration furnace) to compare the displayed value with the actual value. If the deviation exceeds the allowable range (such as ± 1%), it needs to be replaced or recalibrated.
Inspection position: Ensure that the thermocouple temperature measuring end is located at the center of the furnace tube and does not touch the furnace wall or sample, to avoid local overheating or cold end interference.

Temperature control system malfunction
Phenomenon: The temperature control is unstable (such as overshoot, oscillation) or the set value does not match the displayed value.
Troubleshooting:
PID parameter adjustment: If the system uses PID control, check whether the parameters (P, I, D) are reasonable. You can try restoring the factory settings or resetting the parameters.
Controller malfunction: Check the controller display screen for error codes (such as overload, short circuit), and replace the controller if necessary.
Relay/Solid State Relay (SSR): Test whether the relay is frequently turned on or off or damaged, causing unstable heating power.

Furnace structure issues
Phenomenon: The temperature distribution inside the furnace is uneven, and there is a large difference between the displayed temperature and the actual temperature in the area.
Troubleshooting:
Thermocouple location: Confirm whether the temperature measurement point represents the temperature of the target area (such as the sample location). If multiple temperature measurement points are required, the number of thermocouples can be increased.
Furnace tube material: Quartz furnace tubes may deform at high temperatures, causing the position of thermocouples to shift, and the furnace tube condition needs to be checked regularly.
Insulation layer: Check whether the insulation material is aging or damaged, causing heat loss and affecting temperature uniformity.

External disturbances
Phenomenon: Temperature display shows random fluctuations or fixed deviations.
Troubleshooting:
Electromagnetic interference: Keep away from strong electromagnetic sources such as frequency converters and motors, or use shielded cables to connect thermocouples.
Power supply fluctuation: Check if the power supply voltage is stable and install a voltage regulator if necessary.

Operation and maintenance issues
Phenomenon: The temperature deviation gradually increases with usage time.
Troubleshooting:
Regular calibration: It is recommended to calibrate thermocouples and controllers every 6-12 months.
Cleaning the furnace: Accumulated impurities may affect heat conduction, and it is necessary to regularly clean the furnace tubes and thermocouple protective covers.
Sample impact: If the thermal conductivity of the sample is poor or the volume is too large, it may cause local temperature to be too low, and the sample placement method needs to be optimized.

2. Quick Solution
Short term emergency:
If the deviation is fixed (such as displaying 50 ℃ higher than the actual value), the set value can be manually adjusted to compensate for the deviation (if the target temperature is 1000 ℃ and the actual required temperature is 950 ℃, then set it to 1050 ℃).
Use a portable infrared thermometer or contact thermometer to assist in verifying the actual temperature.
Long term repair:
Replace damaged thermocouples or controllers.
Repositioning thermocouples or adding temperature measurement points.
Contact the manufacturer for professional calibration or repair.

3. Preventive measures
Operating standards:
Avoid frequent opening and closing of the furnace door to reduce temperature fluctuations.
The heating rate should not be too fast (recommended ≤ 10 ℃/min) to prevent thermal shock damage to the thermocouple.
Maintenance plan:
Record historical data on temperature deviation, analyze trends to detect problems in advance.
Regularly check whether the insulation layer of the thermocouple is damaged to prevent short circuits.
Spare parts management:
Reserve commonly used models of thermocouples and compensating wires to shorten maintenance time.

4. Example scenario
Problem: The tube furnace displays 1000 ℃, but the sample has not melted (actual temperature required is 1050 ℃).
Troubleshooting:
The surface temperature of the furnace tube measured by an infrared thermometer is 980 ℃, and the displayed value is too high.
Checking the thermocouple connection, it was found that the compensating wire joint was oxidized, causing signal attenuation.
After replacing the compensation wire and recalibrating, the displayed temperature is consistent with the actual value.
Through system troubleshooting and targeted maintenance, temperature inconsistency issues can be effectively resolved to ensure the reliability of experiments or production processes.

Rotating atmosphere tube furnace (click on the image to view product details)

In general, the inconsistency between the displayed temperature and the actual temperature of the tube furnace may be caused by multiple reasons. If the fault cannot be eliminated, you can check the nameplate behind the tube furnace and contact the original technical manufacturer to provide a more accurate solution!Click to learn more tube furnaces! Or click on online customer service to learn more about product information!