After correctly wiring and powering on according to the instrument wiring diagram, the instrument first displays the thermocouple index number of the instrument, then displays the instrument range, and then the digital tube in the lower row of the instrument displays the set temperature, and the digital tube in the upper row of the instrument displays the measured temperature. If the digital display on the instrument panel shows "OVER", "0000" or "000" instead of the temperature of the heating element, it indicates that there is a fault in the input part of the instrument, and the following tests should be conducted:

1) Remove the thermocouple from the input end of the instrument thermocouple and short-circuit the input end of the instrument thermocouple with any wire. When powered on, if the digital display on the instrument panel shows a value of about room temperature, it indicates that the internal wiring of the thermocouple is open and should be replaced with a thermocouple of the same type. If the above situation persists, it indicates that the input end of the instrument was damaged during transportation and needs to be replaced.

2) Remove the thermocouple from the faulty instrument mentioned above and replace it with a thermocouple connected to a nearby instrument with the same calibration number that is running normally. After powering on, if the digital display on the upper row of the faulty instrument shows the temperature of the heating element, it indicates that the thermocouple connection is open. Replace it with a thermocouple of the same type.

3) Remove the faulty thermocouple from the instrument and place it in the ohm (R) * 1 range using a multimeter. Use two multimeter sticks to measure the two ends of the thermocouple. If the resistance value displayed on the multimeter is high, it indicates an open circuit in the internal connection of the thermocouple. Replace it with a thermocouple of the same type. Otherwise, if there is a certain resistance value, it indicates that there is a problem with the input terminal of the instrument and the instrument should be replaced.

4) Connect the wires correctly according to the instrument wiring diagram. If the digital display on the upper row of the instrument shows negative values after the instrument is powered on, it indicates that the thermocouple "+" and "-" connected to the instrument are connected incorrectly. Just swap it again.

5) When the wiring is correct and the instrument is in operation, the temperature displayed on the digital display on the instrument panel differs from the actual measured temperature by 40 degrees to 70 degrees. Even greater differences indicate that the scale of the instrument is incorrect compared to the scale of the thermocouple. According to the corresponding relationship between the temperature and millivolt (MV) value of thermocouples with scale marks B, S, K, E, etc., under the same temperature, the generated MV value is the smallest for scale marks B, the second smallest for scale marks S, the largest for scale marks K, and the largest for scale marks E. This principle is used for discrimination.