After trying a thermocouple for a period of time, it is clear that it will be damaged or even damaged. The quality of some thermocouples is related to the thermocouple wire (wire) outside it. For everyone, let's briefly introduce how to judge the quality of a thermocouple:
At first, judge whether the surface of the thermocouple wire does not have an exam score. It is good or bad. It can only be judged after the entire process is tested.
Put the thermocouple wire to be tested on the common porcelain waterproof sleeve of the thermocouple, put it into the tube-type heating furnace together with the mesoscale platinum rhodium thermocouple, and pull the hot end out of a porous structure in the tube-type heating furnace. Soaking in a cylinder made of nickel, a metallic material. Place the cold ends of the respective filled power lines into a zero-degree Celsius vessel that is persistent with a mixture of cold water.
The tube-type heating furnace is unremittingly at the lowest temperature allowed for the thermocouple, and it is firmly and persistently. During this time, the difference between the thermoelectric potential generated by the mesoscale thermocouple and the thermocouple to be measured was measured and described using a proven Wheatstone multimeter.
According to the described thermoelectric potential difference, check the index table to find the matching temperatures respectively. If the measured thermocouple deviations, it can be judged as a contradiction grid.
How to distinguish the advantages and disadvantages of thermocouples
There are also several types of that can be emulated: distinguishing the advantages and disadvantages of thermocouples
1. Check with human eyes to see if the cable protection tube is etched and penetrated, whether it is water seepage, etc.
2. Use a multimeter to measure the continuity. Generally, assembled thermocouple resistors do not exceed 2 ohms, and network wire resistors do not exceed 50 ohms. Generally more than 1K can be clearly broken.
3. Use a multimeter to measure the resistance. Resistors exceeding 100K are considered bad.
4. Measure with the multimeter European mother measurement method, adjust the resistance, connect to both sides, and lightly heat it with a lighter. If the multimeter's needle significantly increases or decreases, this indicates that it should be good, and the needle does not move to indicate that it has been broken.
5. Use the multimeter millivolt range to measure the voltage at both ends. If there is no working voltage, it will be bad.
6. Remove the thermocouple from the input terminal of the instrument thermocouple, and then use a power line to short-circuit the input terminal of the instrument. When plugged in, when the value displayed by the digital tube below the meter is about the room temperature, it indicates that the internal wiring of the thermocouple is routed, and the same type of thermocouple should be replaced. If it is still the case, it means that the input end of the meter is damaged during the entire transportation of the meter, and the meter must be replaced.
7. Remove the thermocouple of the common faulty instrument and use a thermocouple connected to the same indexing instrument that works normally on the side. After plugging in, the lower digital tube of the original common faulty instrument displays the information about the temperature of the heater. , It indicates that the thermoelectric coupling wire is routed, and the same type of thermocouple is replaced.
8. Remove the thermocouple with common faults from the instrument, use a multimeter to measure the European mother (R) * 1 level, and use the two multimeter rods to measure both sides of the thermocouple. If the resistance value displayed on the multimeter is very large, , Indicating that the thermocouple is internally connected and guided, and the same type of thermocouple is replaced. Otherwise, there is a certain resistance, indicating that the input end of the meter is not good, and the meter should be replaced.
9. The wiring according to the meter wiring method is proper. If the meter is plugged in, the digital display on the lower row of the meter has a negative number, which indicates that the thermocouple “+” and “-” connected to the meter are incorrectly inserted. If you can replace it again.
10. Appropriate wiring When the instrument is in operation, the temperature displayed by the digital tube below the instrument is 40 to 70 degrees from the actual measured temperature. Even the distance is larger, indicating that the graduation number of the meter and the graduation number of the thermocouple are wrong. According to the matching relationship between the thermocouple graduation number B, S, K, E and other thermocouple temperature and millivolt (MV) value, it seems that the same temperature condition caused the millivolt value (MV) B graduation number At least, the S index number is small, the K index number is large, and the E index number is large.
How to distinguish the advantages and disadvantages of thermocouples
According to the relevant technical specifications, it is a standard metrological verification for compulsory metrological verification, which involves saving resources and production safety. Generally, it is required to send the metrological verification to the metrological verification testing center for one year. The key components commonly used for temperature measurement are thermal resistance and thermocouples. Their mutual characteristic is that the two outputs (sometimes cross-platform) are connected through a multimeter (although there is a certain resistance). If the route is bad, there is no doubt that it is the first process to actually distinguish the good from the bad. The thermal resistance is constant, such as PT100 is around 110 ohms at normal temperature, and CU50 is about 55 ohms at room temperature. The output of the thermocouple is the working voltage value. It can output a working voltage data signal of several to several tens of millivolts at a certain temperature, which can be measured by the working voltage range of a multimeter. The output voltage of the thermocouple can only be a few mV, depending on the accuracy of the multimeter. The digital multimeter can be used for rough measurement to distinguish good and bad. The output of a thermocouple is millivolts. It is not possible to test his output with a multimeter, but it can measure its continuity. In most cases, if a part of the galvanic couple (dissolved at the intersection of the two wires) is open, there is no air oxidation, and it is not bad, generally everything is normal. Therefore, it can also be removed from the protective cover for appearance inspection. To check the truth, we need to use a standard thermocouple to compare and measure the millivolt output. This also requires the staff engaged in metrological verification.
Some multimeters have thermocouple files. If you do n’t check the surface condition of the thermocouple, check whether the thermocouple is broken. If both are good, you can put the thermocouple in two areas with a large temperature difference. Use the multimeter MV file to check it and put it in In different places, the mV is significantly different (generally difficult to measure), and you can feel that the thermocouple is everything normal. If the thermal resistance is placed in two regions with significant temperature differences, measure its resistance value and understand the pros and cons of the index table. If it is to be determined with high precision, it must be inspected by professional machinery and equipment or by the Quality and Technical Supervision Bureau.