In general, the failure of the thermocouple is divided into the following situations:
First, the thermoelectric potential is smaller than the actual value
1. Reason analysis:
(1) Short circuit; (2) Short circuit between terminals in the thermocouple junction box; (3) Short circuit of compensation wire due to insulation burnout;
(4) The compensation wire does not match the thermocouple; (5) The polarity of the compensation wire and the thermocouple is reversed; (6) The insertion depth is not enough and the installation position is wrong; (7) The temperature of the cold junction of the thermocouple is too high.
2. Treatment method:
(1) After inspection, if it is caused by humidity, it can be dried; if it is due to poor insulation of the porcelain tube, it should be replaced;
(2) Open the junction box and brush the wiring board clean; (3) Re-insulate the short circuit or replace with a new compensation wire;
(4) Replace with the same type of compensation wire; (5) Reconnect correctly;
(6) Change the installation position and insertion depth; (7) Replace the connecting wire of the thermocouple with a compensation wire to move the cold end away from the high temperature area.
Second, the thermoelectric potential is larger than actual
1. Reason analysis:
(1) The compensation wire does not match the thermocouple model; (2) The insertion depth is not enough or the installation position is wrong;
(3) Deterioration of the hot electrode; (4) Interference signal enters; (5) The temperature of the reference terminal of the thermocouple is too high.
2. Treatment method:
(1) Replace the compensation wire of the same model; (2) Change the installation position or insertion depth;
(3) Replace the thermocouple; (4) Check the interference source and eliminate it; (5) Adjust the reference terminal temperature or make corrections.
Third, the indication of the measuring instrument is unstable, sometimes no, sometimes high and sometimes low
1. Reason analysis:
(1) The thermoelectrode is in poor contact at the terminal; (2) The thermocouple has intermittent short circuit or intermittent grounding;
(3) The thermoelectrode is broken or seems to be broken but not broken; (4) The thermocouple is not firmly installed and swings;
(5) The compensation wire is grounded or intermittently short-circuited.
2. Treatment method:
(1) Reconnect it; (2) Take out the hot electrode of the thermocouple from the protection tube, find out the fault point and eliminate it;
(3) Replace with new electrodes; (4) Install firmly; (5) Find out the fault point and eliminate it.
Fourth, the thermocouple electric potential error is large
1. Reason analysis:
(1) Deterioration of the thermoelectrode; (2) Improper installation position and method of thermocouple;
(3) The surface area of the thermocouple protection sleeve is too dirty; (4) The measuring circuit is short-circuited (thermocouple and compensation wire);
(5) The thermocouple circuit is disconnected; (6) The terminal is loose.
2. Treatment method:
(1) Replace the thermocouple; (2) Change the installation location and method;
(3) Clean up; (4) Replace the insulation at the short-circuit;
(5) Find the broken wire and reconnect it; (6) Tighten the terminal.
