The positive and negative misuses of thermocouples on industrial furnaces
1. Fault Instance
A resistance furnace is periodically verified, qualified to continue to use the original position, after reinstallation, test run, temperature measurement system can not run normally, no temperature display.
2. Fault site treatment and cause analysis
(1) Processing method
Such equipment failure problems mainly from the perspective of equipment installation to find the cause. Field observation revealed that the pointer of the indicator was deflected in the direction, indicating that the connection between the sensor and the indicator was smooth. Millivoltmeter respectively measuring thermocouple output terminal and the input terminal of the meter, confirm the thermocouple is negative and the reverse, raises the temperature after connecting, and found that the temperature indicating value is less than the actual temperature in the furnace, eliminate thermocouple cold forging compensation and zero point correction of possible problems, identified as thermocouple compensating lead wires across the electrodes for reverse connection, adjust the connection, electric furnace temperature control system back to normal.
(2) Cause analysis
Thermocouple and compensation wire work by different metals producing different potentials at the same temperature difference. Thus the thermocouple and the supporting compensation wire have positive and negative polarity relative to the output end. Reverse polarity connection will cause meter display error. In this case, the polarity error of the thermocouple makes the instrument reverse, showing that the temperature is not displayed; After the first adjustment, the polarity of the supporting compensation wire was not adjusted at the same time, resulting in the reverse superposition of the electric potential and the indicating temperature of the instrument being lower than the actual temperature.
3. Points revealed by Fault 3
Point 7: The hot couple and compensation wire are polar, can not be connected to the opposite.
Point 8: Compensation wire and thermocouple should have the same polarity.
Point 9: When conducting thermocouple check, it is best to check together with the on-site supporting compensation wire.
On 2018-08-08 11:45:46
