Thermocouple fault discrimination method1

The temperature of the thermocouple is a kind of common measuring instruments, can directly measure the temperature, and the temperature signals into a thermoelectric emfs. Thermocouple also can appear some fault in the course of using, the user for the fault distinguish method need to master, the project is to introduce thermocouple failure to identify specific methods.

thermocouple failure to identify methods:

in accordance with the instrument to correct connection electric wiring diagram, first instrument display instrument of thermocouple indexing number, and then display instrument range limits, and then measuring instrument discharge of digital tube display set temperature, the digital tube display on the meter measuring temperature.

if digital tube display on the meter is not the temperature of the heating element, and show 'OVER', '0000' or '000' and so on, explain instrument malfunction, input parts should be done the following test:

1) The thermocouple from the meter thermocouple input to be removed, then the instrument with any wire thermocouple input terminal short circuit. On the electricity, instrument digital tube display value approximately at room temperature, thermocouple internal connection open circuit, the same type thermocouple should be changed. If still the status of the said above that instrument in the process of transportation, the input end of the instrument is damaged, to change the instrument.

2) The above fault instrument of thermocouple down, switch to run next to normal the same degree, access to the instrument of thermocouple, after electrify, the original fault instrument digital tube display on the heating element temperature, thermocouple wire open, replace the same type thermocouple.

3) The defective thermocouple removed from the instrument, measured with a multimeter in ohms ( R) * 1 file, use multimeter thermocouple at both ends, two table stick to test if the multimeter display on resistance value is very big, thermocouple internal connection open circuit, replace the same type thermocouple. Or have a certain value, the instrument input has a problem, should replace the instrument.

4) According to the instrument wiring diagram wiring is correct, if the instrument after electrify, digital tube display meter race such as negative phenomenon, illustrate access instrument thermocouple '+' and '- 'Wrong. Just need to change.

5) Wiring correct instrument at run time, the temperature of the instrument on the digital tube display and the actual measurement of the temperature difference of 40 ℃ ~ 70 ℃. Even bigger difference, the instrument of indexing, and thermocouple dividing, make a mistake. By thermocouple indexing, B, S, K, E, etc. The temperature of the thermocouple and the millivolt ( MV) The value of the corresponding relation, under the condition of same temperature, the millivolt values ( MV) B the minimum degree, S degree, small, K index number is larger, E index number, the largest discriminant according to this principle.

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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor