1. The temperature is set and displayed normally, but the oil bath is not heating. First, check the screen display. Turn on the power, set the desired temperature 20°C higher than the normal operating temperature, and observe whether the heating indicator light turns on. If it does, this indicates that the heating element may be damaged or the relay contact has worn out due to long-term use. This can prevent proper heating. To confirm, you can use a multimeter in resistance mode (set to 10 ohms) to measure the resistance of the heating element. For an oil bath heater, the resistance should typically be less than 100 ohms. If the resistance is high, the heating element is likely broken. If the resistance is normal, the problem is most likely with the relay, which needs to be replaced.
2. The temperature setting and measurement are normal, but the temperature keeps rising beyond the set point. This is common during the first use of an oil bath with a microcomputer PID control system, where over-temperature may occur but usually doesn't exceed 10°C. A self-tuning process is required for optimal performance. Once the set temperature is reached, check if the heating indicator light turns off. If it does, the temperature controller is working properly, and only the relay may need replacement. However, if the light remains on, the temperature controller itself is likely faulty and needs to be replaced.
3. After some time of use, the oil bath fails to heat up. This is often caused by increased resistance in the heating element or rusted connections leading to high contact resistance. In such cases, the heating element should be replaced, or the connection points should be cleaned and reconnected. Visual inspection can help identify the issue, especially if there are signs of oxidation or damage at the joints.
4. After setting the temperature, the display shows a drop in temperature, but the actual temperature is still increasing. This phenomenon typically occurs when using a K-type sensor. PT100 sensors do not exhibit this behavior. It may happen after replacing the sensor, so check if the positive and negative leads are correctly connected. Reversing the polarity might resolve the issue.
5. The display shows "000" or "999." This usually indicates an open or shorted sensor. In such cases, the sensor should be replaced to restore normal operation.
6. There is no power to the entire unit. Check if the power socket is functioning, if the fuse is intact, and if the power switch is working properly. Most of these issues are caused by a faulty power switch, which should be inspected and possibly replaced.
7. The power indicator is on, but the temperature controller’s screen is blank. Check the output of the LM7805 voltage regulator on the temperature controller. Faults in this area are often due to poor solder joints on the transformer or the LM7805 itself, which is part of the heating circuit. These components should be carefully examined and repaired or replaced as needed.
Additional Note: The above troubleshooting steps apply to both constant temperature and super constant temperature oil baths. In the case of a super constant temperature oil bath with a circulation pump, if the pump does not turn on, it is likely due to a failed capacitor. To test, turn on the power and the circulation pump switch, then manually rotate the motor shaft. If it turns freely, the capacitor is likely bad. If it doesn’t turn, the motor itself may be faulty and requires further inspection.
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