Thermocouple in use for a period of time, there will be wear, and even damage, the advantages and disadvantages of individual thermocouple and its outside thermocouple wire (wire), so how to determine the advantages and disadvantages of thermocouple?
1. Naked eye observation, whether the protection pipe corrosion penetration, whether water leakage.
2. When measuring on-off with a multimeter, the resistance of assembled thermocouple is generally no more than 2 ohm, and that of network wire type is not more than 50 ohm. Generally, if it is greater than 1K, it can be determined that it is broken.
3. Measure the resistance with a multimeter. If the resistance exceeds 100k, it will be broken.
4. Use the ohmmeter ohm measurement method to measure, adjust the resistance, connect the two ends, and use a lighter to iron down slightly. If the multimeter pointer obviously becomes larger or smaller, it indicates that it is good. If the pointer does not move, it indicates that it is broken.
5. Measure the voltage at both ends with a multimeter in millivolt range. If there is no voltage, it will be broken.
6. Remove the thermocouple from the input end of the instrument thermocouple, and then use any wire to short circuit the input end of the instrument thermocouple. When powered on, the display value of the digital tube on the upper row of the instrument is about room temperature, indicating that the internal wiring of the thermocouple is open, and the same type of thermocouple should be replaced. If it is still in the condition mentioned above, it means that the input end of the instrument is damaged during transportation and the instrument should be replaced.
7. Remove the thermocouple of the above-mentioned fault instrument and replace it with the thermocouple connected to the same graduation meter which is running normally nearby. After power on, when the digital tube on the upper row of the original fault instrument shows the temperature, it indicates that the thermocouple connection is open, and replace the same type of thermocouple.
8. Remove the faulty thermocouple from the instrument, put the multimeter at the measuring ohm (R) * 1, and use two multimeter bars to measure both ends of the thermocouple. If the resistance value shown on the multimeter is large, it indicates that the internal connection of the thermocouple is open, so replace the same type of thermocouple. Otherwise, there is a certain resistance value, indicating that there is something wrong with the input end of the instrument, and the instrument should be replaced.
9. The wiring is correct according to the wiring diagram of the instrument. If the digital tube on the upper row of the instrument shows negative value after the instrument is powered on, it indicates that the thermocouple connected to the instrument "+" and "-" are connected incorrectly. Just change it.
10. The wiring is correct. When the instrument is running, the difference between the temperature displayed by the digital tube on the upper row of the instrument and the actual measured temperature is 40 ~ 70 ℃. The difference is even greater, indicating that the graduation number of the instrument is wrong with that of the thermocouple. According to the corresponding relationship between the temperature of thermocouples such as B, s, K, e and the millivolt (MV) value, under the same temperature condition, the millivolt value (MV) produced by B is the smallest, s is the second, K is larger, and E is the largest.
11. It is concluded that the surface of thermocouple wire is good or bad. The thermocouple wire to be measured is put into the common porcelain sleeve of thermocouple, and put into the tubular furnace together with the standard platinum rhodium thermocouple. The hot end is pulled out of a cylinder made of porous metal nickel for heat soaking in the tubular furnace. Put the cold ends of the respective compensating wires into a zero degree Celsius container held by ice water mixture.
Stick the tube furnace at the minimum allowable temperature of the thermocouple, and firmly adhere to this category. At this time, the thermoelectric potential difference between the scale thermocouple and the thermocouple to be measured is measured and recorded with the Wheatstone potentiometer passing the test.
According to the thermoelectric potential difference recorded, check the index table to find out the corresponding temperature. If the thermocouple to be measured is out of tolerance, it can be determined as a bifurcation lattice.
On 2018-08-08 11:45:46
