WRR-120, WRR-121, WRR-122, WRR-123, WRR-130, WRR-131, WRR-132, WRR-133, WRR-140, WRR-141, WRR-142, WRR-143, WRR-220, WRR-221, WRR-222, WRR-223, WRR-230, WRR-231, WRR-232, WRR-233, WRR-240, WRR-241, WRR-242, WRR-243, WRR-320, WRR-321, WRR-322, WRR-323, WRR-330, WRR-331, WRR-332, WRR-333, WRR-340, WRR-341, WRR-342, WRR-343, WRR-420, WRR-421, WRR-422, WRR-423, WRR-430, WRR-431, WRR-432, WRR-433, WRR-440, WRR-441, WRR-442, WRR-443, WRR-520, WRR-521, WRR-522, WRR-523, WRR-530, WRR-531, WRR-532, WRR-533, WRR-540, WRR-541, WRR-542, WRR-543, WRR-620, WRR-621, WRR-622, WRR-623, WRR-630, WRR-631, WRR-632, WRR-633, WRR-640, WRR-641, WRR-642, WRR-643, WRP-120, WRP-121, WRP-122, WRP-123, WRP-130, WRP-131, WRP-132, WRP-133, WRP-140, WRP-141, WRP-142, WRP-143, WRP-220, WRP-221, WRP-222, WRP-223, WRP-230, WRP-231, WRP-232, WRP-233, WRP-240, WRP-241, WRP-242, WRP-243, WRP-320, WRP-321, WRP-322, WRP-323, WRP-330, WRP-331, WRP-332, WRP-333, WRP-340, WRP-341, WRP-342, WRP-343, WRP-420, WRP-421, WRP-422, WRP-423, WRP-430, WRP-431, WRP-432, WRP-433, WRP-440, WRP-441, WRP-442, WRP-443, WRP-520, WRP-521, WRP-522, WRP-523, WRP-530, WRP-531, WRP-532, WRP-533, WRP-540, WRP-541, WRP-542, WRP-543, WRP-620, WRP-621, WRP-622, WRP-623, WRP-630, WRP-631, WRP-632, WRP-633, WRP-640, WRP-641, WRP-642, WRP-643, WRN-120, WRN-121, WRN-122, WRN-123, WRN-130, WRN-131, WRN-132, WRN-133, WRN-140, WRN-141, WRN-142, WRN-143, WRN-220, WRN-221, WRN-222, WRN-223, WRN-230, WRN-231, WRN-232, WRN-233, WRN-240, WRN-241, WRN-242, WRN-243, WRN-320, WRN-321, WRN-322, WRN-323, WRN-330, WRN-331, WRN-332, WRN-333, WRN-340, WRN-341, WRN-342, WRN-343, WRN-420, WRN-421, WRN-422, WRN-423, WRN-430, WRN-431, WRN-432, WRN-433, WRN-440, WRN-441, WRN-442, WRN-443, WRN-520, WRN-521, WRN-522, WRN-523, WRN-530, WRN-531, WRN-532, WRN-533, WRN-540, WRN-541, WRN-542, WRN-543, WRN-620, WRN-621, WRN-622, WRN-623, WRN-630, WRN-631, WRN-632, WRN-633, WRN-640, WRN-641, WRN-642, WRN-643, WRE-120, WRE-121, WRE-122, WRE-123, WRE-130, WRE-131, WRE-132, WRE-133, WRE-140, WRE-141, WRE-142, WRE-143, WRE-220, WRE-221, WRE-222, WRE-223, WRE-230, WRE-231, WRE-232, WRE-233, WRE-240, WRE-241, WRE-242, WRE-243, WRE-320, WRE-321, WRE-322, WRE-323, WRE-330, WRE-331, WRE-332, WRE-333, WRE-340, WRE-341, WRE-342, WRE-343, WRE-420, WRE-421, WRE-422, WRE-423, WRE-430, WRE-431, WRE-432, WRE-433, WRE-440, WRE-441, WRE-442, WRE-443, WRE-520, WRE-521, WRE-522, WRE-523, WRE-530, WRE-531, WRE-532, WRE-533, WRE-540, WRE-541, WRE-542, WRE-543, WRE-620, WRE-621, WRE-622, WRE-623, WRE-630, WRE-631, WRE-632, WRE-633, WRE-640, WRE-641, WRE-642, WRE-643, WRN-230 thermocouple is a commonly used temperature measuring component in a temperature measuring instrument. It directly measures the temperature and converts the temperature signal into a thermoelectromotive force signal, which is converted into the temperature of the measured medium by an electric meter (secondary meter). The shape of various thermocouples is often very different due to the needs, but their basic structure is almost the same, usually composed of hot electrode, insulating sleeve protection tube and junction box, etc., usually with display instrument, recording instrument and electronic adjustment Used in conjunction with the device.
In industrial production, temperature is one of the important parameters that need to be measured and controlled. In the temperature measurement, the thermocouple is widely used, and it has many advantages such as simple structure, convenient manufacture, wide measuring range, high precision, small inertia and easy transmission of output signals. In addition, since the thermocouple is a passive sensor, it does not need an external power supply for measurement. It is very convenient to use, so it is often used to measure the temperature of the gas or liquid in the furnace, the pipe, and the surface temperature of the solid.
When there are two different conductors or semiconductors A and B form a loop, when the two ends are connected to each other, as long as the temperature at the two junctions is different, the temperature at one end is T, which is called the working end or the hot end, and the temperature at the other end is T0. It is called the free end (also called the reference end) or the cold end. An electromotive force is generated in the loop. The direction and magnitude of the electromotive force are related to the material of the conductor and the temperature of the two joints. This phenomenon is called "thermoelectric effect". The circuit composed of two kinds of conductors is called "thermocouple". These two kinds of conductors are called "hot electrodes", and the generated electromotive force is called "thermoelectromotive force".
The thermoelectromotive force consists of two partial electromotive forces, one of which is the contact electromotive force of the two conductors, and the other is the temperature difference electromotive force of the single conductor.
The magnitude of the thermoelectromotive force in the thermocouple loop is only related to the temperature of the conductor material and the two junctions that make up the thermocouple, regardless of the shape and size of the thermocouple. When the thermocouple two electrode materials are fixed, the thermoelectromotive force is the two junction temperatures t and t0. The function is poor. This relationship has been widely used in actual temperature measurement. Since the cold terminal t0 is constant, the thermoelectromotive force generated by the thermocouple changes only with the temperature of the hot end (measuring end), that is, a certain thermoelectromotive force corresponds to a certain temperature. We only need to measure the thermoelectromotive force to achieve the purpose of temperature measurement.
The basic principle of thermocouple temperature measurement is that the material conductors of two different compositions form a closed loop. When there is a temperature gradient at both ends, there will be current flowing through the loop. At this time, there is an electromotive force between the two ends - the thermoelectromotive force. It is the so-called Seebeck effect. The homogeneous conductor of two different compositions is a hot electrode, the higher temperature end is the working end, the lower temperature end is the free end, and the free end is usually at a constant temperature. According to the relationship between the thermoelectromotive force and the temperature, the thermocouple index table is prepared; the index table is obtained under the condition that the free end temperature is 0 ° C, and different thermocouples have different index tables.
When a third metal material is connected to the thermocouple loop, as long as the temperature of the two contacts of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, not affected by the third metal access loop. Therefore, when the thermocouple is measuring temperature, the measuring instrument can be connected, and after measuring the thermoelectromotive force, the temperature of the measured medium can be known. When the thermocouple measures the temperature, the temperature of the cold end (the measuring end is the hot end, the end connected to the measuring circuit through the lead wire is called the cold end) is kept constant, and the thermoelectric potential is proportional to the measured temperature. If the temperature of the cold end (environment) changes during the measurement, the accuracy of the measurement will be seriously affected. Some measures are taken at the cold end to compensate for the effect of the cold junction temperature change, which is called the cold junction compensation of the thermocouple. A dedicated compensation wire for connection to the measuring instrument.
1. Simple assembly and convenient replacement;
2, pressure spring type temperature sensing element, good seismic performance;
3. High measurement accuracy;
4, the measurement range is large (-200 ° C ~ 1300 ° C, in special cases -270 ° C ~ 2800 ° C);
5, the thermal response time is fast;
6. High mechanical strength and good pressure resistance;
7, high temperature resistance up to 2800 degrees;
8, long service life.
For the installation of thermocouples and RTDs, attention should be paid to the accuracy of temperature measurement.
It is safe, reliable and easy to maintain, and does not affect the operation and production operation of the equipment. To meet the above requirements, pay attention to the following points when selecting the installation location and insertion depth of the thermocouple and the thermal resistance:
1. In order to ensure sufficient heat exchange between the measuring end of the thermocouple and the thermal resistance and the measured medium, the position of the measuring point should be reasonably selected to avoid installing thermocouples near the dead angle of valves, elbows and pipes and equipment. Thermal resistance.
2. Thermocouples and thermal resistors with protective sleeves have heat transfer and heat loss. To reduce measurement errors, thermocouples and RTDs should have sufficient insertion depth:
(1) For thermocouples that measure the temperature of the fluid at the center of the pipe,
Generally, the measuring end should be inserted into the center of the pipe (vertical or inclined installation). If the pipe diameter of the fluid to be tested is 200 mm, the insertion depth of the thermocouple or thermistor should be 100 mm;
(2) For the temperature measurement of high temperature and high pressure and high speed fluid (such as main steam temperature), in order to reduce the resistance of the protective sleeve to the fluid and prevent the protective sleeve from breaking under the action of the fluid, the protective tube may be inserted in a shallow insertion manner or a hot sleeve. Thermocouple, shallow-plug thermocouple protection sleeve, the depth of insertion into the main steam pipe should not be less than 75mm; the standard insertion depth of the thermo-sleeve thermocouple is 100mm;
(3) If it is necessary to measure the temperature of the flue gas in the flue, although the diameter of the flue is 4 m, the insertion depth of the thermocouple or thermistor can be 1 m;
(4) When the insertion depth of the measuring element exceeds 1 m, it should be installed as perpendicular as possible, or the support frame and the protective sleeve should be added.