Instrumentation: [Question of the Week] Week 24, 2011: The temperature instrument gives inaccurate readings – how to determine the issue?
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This post was last edited by siena2008 on 2011-7-12 at 10:36. The operator reported that the temperature indicated by the gauge is inaccurate; how do you determine whether it is the gauge itself that is faulty? (Measured with a thermocouple)] Answer: First, use the temperature equation E(t,0) = (t, t0) + E(t0,0) to determine the room temperature; then consult the manual to find the millivolt value at (t0,0), and subsequently use a digital multimeter to measure the millivolt value at the cold end of the thermocouple at (t, t0). Using E=(t,t0)+(t0,0) gives the temperature that the instrument should indicate. When the instrument’s reading corresponds to the resulting millivolt value, it is considered that the instrument’s reading is accurate; if the reading does not correspond to the millivolt value, then there is a problem with the instrument.
This post was last edited by denghl on 2012-12-21 at 21:15. Measure the thermoelectric potential, check the corresponding temperature using a thermocouple chart, and inspect the compensation wire.
Compare the difference with the on-site thermometer, inquire about the reason for the inaccurate start time, and check whether the process conditions have changed. Considering the service life of the instrument, test it using a signal generator
Check whether the potential of the thermocouple corresponds to the current temperature, inspect whether water has entered the protective sheath at the installation site, check if the cable is grounded, and finally, it can be removed for temperature verification using a temperature testing chamber.
Check whether the potential of the thermocouple matches the current temperature
In three steps: first, check whether the wiring is intact; second, check whether the temperature sensing element is functioning properly; finally, check the channels of the system. Also, if the curve record is a straight line, it’s definitely a problem with the instrument.
The last edit to this post was made by denghl on 2012-12-21 at 21:17: 1. Check whether the thermocouple has poor contact or an open circuit, and whether there is proper insulation between the thermal electrode and the ground； 2. View the record curve ； 3. Comparison test with in-situ thermometer
Compare with the on-site indicating thermometer there
1. Measure the MV signal at the terminal in the control room; the value of MV obtained in this way, plus the MV value corresponding to the temperature in the control room, gives the actual temperature in MV terms. Then check whether the temperature indicated by this value matches the temperature listed in the table. 2. Check whether the insertion depth of the thermocouple is appropriate. 3. Verify that the wiring is secure and there is no grounding issue, in order to prevent interference potentials from entering. 4. Check whether the resistance value of the thermocouple is normal; it should not be too high, as a high resistance value will result in false potential readings, indicating that the thermocouple is improperly connected
In my opinion, the most important thing is to ask the process engineers about the situation before and after the change, to see if there are any fluctuations in the system. Then check whether water has entered the catheter at the site and if there is any grounding issue. If possible, use a good thermocouple to measure the actual temperature; if no 726 is available, use a multimeter. Also check the dial gauge, as this will show whether the gauge is inaccurate.
This post was last edited by denghl on 2012-12-21 21:18 to check if the wires are intact