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A thermocouple is a circuit formed by joining two conductors of two different components into a loop. When the temperatures of the two junctions are different, a thermal current is generated in the loop. If there is a temperature difference between the working end and the reference end of the thermocouple, the display meter will indicate the temperature value corresponding to the thermoelectric potential generated by the thermocouple.
The thermoelectric heat of the thermocouple will increase as the temperature at the measuring end increases. The size of the explosion-proof thermocouple is only related to the temperature of the thermocouple material and both ends, and is independent of the length and diameter of the thermode.
The appearance of various thermocouples is often very different due to the need, but their basic structure is roughly the same, usually composed of the main components of the hot electrode, low temperature coolant circulating pump insulating sleeve protection tube and junction box.
Thermocouple input fault identification method according to the instrument wiring diagram for correct wiring After power, the instrument is first to display the instrument thermocouple index number, then display the instrument range, and then test the instrument under the digital display temperature settings, the instrument upper row The digital tube shows the measuring temperature. Magnetic stirrer If the digital display on the upper row of the instrument is not the temperature of the heating element, and the status of “OVERâ€, “0000†or “000†is displayed, indicating that the input part of the instrument is faulty, the following test should be performed:
A) Remove the thermocouple from the input of the instrument thermocouple and short-circuit the input of the thermocouple to any of the wires. When the power is on, the digital value displayed on the upper row of the meter is about room temperature, indicating that the thermocouple's internal connection is open and the same type of thermocouple should be replaced. If it is still the above-mentioned condition, it means that the meter's input terminal is damaged during the transportation process, and the meter must be replaced.
B) Remove the thermocouple of the above-mentioned fault meter and replace the thermocouple connected to the instrument with the same kind of index number running next to the thermocouple. After the power is turned on, the upper digital tube of the original micro-thermocouple will display the temperature of the heating element. Note that the thermocouple's internal connection is open and the same type of thermocouple is replaced. If it is still the above-mentioned condition, it means that the meter's input is damaged during the transportation process, and the meter should be replaced.
C) Remove the faulty thermocouple from the meter, use a multimeter to measure ohms (R)*1, and use the two multimeters of the multimeter to measure the two ends of the thermocouple. If the resistance value displayed on the multimeter is very large, it means that Thermocouple internal connection open circuit, replace the same type of thermocouple. Otherwise there is a certain resistance, indicating that there is a problem with the input of the instrument, and the instrument should be replaced.
2) According to the wiring diagram of the meter, the wiring is correct. If the meter is powered on, the digital tube on the meter shows a negative value, indicating that the thermocouple “+†and “—†connected to the meter are connected incorrectly. Just change it again.
3) Correct wiring When the instrument is in operation, the temperature displayed by the digital tube on the top of the assembled thermocouple meter is different from the actual measured temperature by 30oC~60oC. The difference is even greater, indicating that the meter's index number is wrong with the thermocouple's index number. According to the temperature (oC) and millivolt (MV) values ​​of the thermocouple index numbers B, S, K, E, etc., the millivolt value (MV) of the same temperature (oC) ) The B-index number is the smallest, the S-index number is smaller, the K-division number is larger, and the E-division number is the largest, according to this principle.
1: Theoretically, different materials lead to problems in accuracy, but the chance of actually having problems is not large. I often use ordinary two-core 0.5 power cords to weld without problems.
2: If the actual situation at the scene requires a long time, you should increase the length of the thermocouple line at the time of ordering so as to avoid errors in the measurement. 3: The results will definitely be biased! Just no comparison, you can't see it! The signals we measure are all Is a relative value, not absolute! Absolute accuracy is not.
4: It seems that the landlord has some problems in understanding the thermocouple wire. When the thermocouple wire is not long enough, the copper wire can be used, but the place where the copper wire and the raw material are connected becomes a cold end, and the cold end compensation is needed. The thermoelectricity of the S7200 The terminal of the even module is not connected to the compensation signal. I personally think that the S7200 is only suitable for occasions where the thermocouple is not connected to the copper wire because it can only use the internal compensation of the module and cannot use external compensation. The wire is not long enough and copper is added. Line, you must use external compensation, or certainly not allowed.
5: I measured the resistance of the unit length of the original thermocouple wire is relatively large, may not be our ordinary wire. As you said, "where copper and raw materials are connected, they become cold ends and require cold-junction compensation." I think that the two lines are not indoors at the heating site. It should be a cold-end compensation of the PLC. Otherwise, according to the logic of the pure theory, there is wiring aluminum terminal on the thermocouple wire (as soon as it is bought)
The performance of pressure transmitters, such as reliability, accuracy, long-term drift, and overvoltage protection capabilities, are constantly improving and getting better and better. This is especially true of some new high-performance versions. New levels of high performance transmitters are emerging. Paula Hollywood, chief analyst of ARC Advanced Analyst, an explosion-proof thermocouple and research report, defined these high-performance transmitters as products with accuracy higher than ±0,05%. She also pointed out that for the end user, the increased reliability of the transmitter also means less maintenance costs and process uptime.
What is the life cycle of the lifecycle warranty transmitter? Once the supplier begins to provide a full lifecycle warranty on high-end, high-performance transmitters, then such a warranty period will only eliminate the low-level transmitters. Problem. It can be expected that today's advanced technology used only in high-end transmitters will become commonplace in future low-grade transmitters.
The traditional difference between thick-film circuit transmitters and popular pressure sensors and transmitters has become increasingly blurred. From the appearance of people can no longer distinguish them. Their prices have also been comparable. ARC predicts that as the process industry shifts to fieldbus technology,
Thick-film circuit type instrument structures with analog output or voltage output are actually welcome. Pp fume hoods These products are characterized by the fact that the on-site display and programming interfaces are embedded in digital communication protocols, radically reducing packaging costs and selling prices. Because these transmitters are smaller, they can be installed where previous transmitters could not be installed. For example, it can be installed in a car or in a medical device.
In some mature markets, new market drivers have emerged to continuously improve the performance of pressure transmitters, especially new high-performance transmitters. Their accuracy, reliability, long-term drift and overvoltage protection capabilities are getting better and better. . The new market drivers for cryogenic coolant circulation pumps, such as on-site instrument management, on-line analysis, and the needs of some application solutions, will influence the user's ability to update or upgrade existing transmitters. This is particularly important in more developed regions such as North America and Europe. Those regions are basically saturated mature markets, especially where capital expansion is very limited.
Industrial thermocouple input fault diagnosis method
Industrial thermocouples are used as temperature measurement sensors. They are usually used together with temperature transmitters, regulators, and display instruments to form a process control system. Rotary evaporators are used to directly measure or control the range of 0-1800°C in various production processes. Fluid, vapor, and gas media, and solid surfaces, etc.