Functions and uses of various temperature instruments

With the development of modern industry, enterprises have an increasing demand for temperature instruments in industrial production. In order for users to quickly understand the performance of temperature instruments in production, our company briefly introduces the functions and uses, application environment and selection knowledge of various temperature instruments to provide help to users.
Principles for selecting commonly used contact thermometers in industrial production:
1. Meet the requirements for temperature measurement accuracy;
2. Meet the requirements for temperature measurement range;
3. Meet the requirements for indication, recording, alarm and temperature control;
4. Meet the requirements for use environment conditions;
5. Under the above premise, select low-priced, durable and easy-to-maintain instruments.
1. Industrial thermal resistor:
Industrial thermal resistors are usually used in conjunction with display instruments, recording instruments, electronic computers, etc. Directly measure the temperature of liquid, steam and gas media and solid surfaces of machinery and equipment in the range of -200℃~500℃ in various industrial production processes.
Advantages of industrial thermal resistors: imported thin film resistor elements, reliable and stable performance; good mechanical strength and pressure resistance; no compensation wire is required, saving costs.
Industrial thermal resistors The four-wire system can completely eliminate errors by relying on the circuit, while the three-wire system can approximately eliminate errors. The errors of the two-wire system are generally used in places where the accuracy requirements are not high.
2. Industrial thermocouples:
1. Industrial thermocouples are one of the most commonly used temperature detection elements in industry. They must be equipped with secondary instruments. Their advantages are: simple structure and easy use. Industrial thermocouples are usually composed of two different metal wires, and are not limited by size and opening. They have a protective sleeve outside, which is very convenient to use; measurement accuracy. Because industrial thermocouples are in direct contact with the object being measured, they are not affected by the intermediate medium; the measurement range is wide. Commonly used thermocouples can be continuously measured from -50~+1600℃. Some special thermocouples can measure as low as -269℃ (such as gold, iron, nickel, chromium) and as high as +2800℃ (such as tungsten-rhenium).
2. According to the temperature measurement range and accuracy in industrial production, industrial thermocouples with corresponding graduation numbers should be selected. T-type industrial thermocouples are generally used for measurements at 250℃ and negative temperatures. At low temperatures, T-type industrial thermocouples are stable and accurate. E-type industrial thermocouples are generally used below 400℃; K-type industrial thermocouples and N-type industrial thermocouples are generally used below 1000℃; S-type industrial thermocouples and N-type industrial thermocouples can be used when the operating temperature is between 1000 and 1300℃ and the accuracy is relatively high; B-type industrial thermocouples are generally used when the operating temperature is between 1300 and 1800℃ and the accuracy is relatively high; tungsten-rhenium industrial thermocouples can be used when the accuracy is not high and the atmosphere allows it. Tungsten-rhenium industrial thermocouples are generally used above 1800℃;
3. The model of the industrial thermocouple should be consistent with the model of the compensation wire; the protective tube should be selected in detail according to the use environment and temperature. 1Cr18Ni9Ti material is suitable for measuring temperature -200∽800℃, has corrosion resistance, and is usually used as general heat-resistant steel; 304 material is suitable for measuring temperature -200∽800℃, has low carbon content, has good intergranular corrosion resistance, and is usually used as general heat-resistant steel; GH3030 material is suitable for measuring temperature 0∽1100℃. Nickel-based high-temperature alloy steel has excellent oxidation resistance and corrosion resistance, and is usually used as heat-resistant steel.
For medium and low temperatures below 500℃, the thermoelectric potential output of the thermocouple is very small, which is difficult for the amplifier of the secondary instrument to achieve accurate measurement; moreover, in the lower temperature area, the relative error caused by the change of the cold end temperature is also very prominent. Therefore, it is more appropriate to use industrial thermal resistance temperature measuring instruments to measure medium and low temperatures.
4. Selection of use occasions: S-type, B-type, and K-type industrial thermocouples are suitable for use in high temperature, strong oxidation, and weak reduction occasions; J-type and T-type industrial thermocouples are suitable for medium temperature, weak oxidation, and reduction occasions. If a protective tube with better air tightness is used, the requirements for the use occasion are not too strict.
5. Selection of type: Armored industrial thermocouples are suitable for occasions that require vibration or impact resistance, and require improved response speed; assembled industrial thermocouples are suitable for general occasions.
6. Industrial thermocouples with large wire diameters should be selected. They have good durability and a relatively high upper limit of the maximum use temperature, but they respond slowly. When measuring temperatures with large gradients, the temperature control is poor.
3. Pressure thermometer:
The general use range of pressure thermometer is 0~125℃, divided into gas type and liquid type. The use range of gas type is -100~500℃, with 1.0~1.5% accuracy, and the use range of liquid type is -50~500℃, with 1.0~2.5% accuracy. It has a simple structure, average price, good seismic resistance, and can measure the temperature of gas, liquid, and steam in the equipment at a short distance. The instrument scale is clear, and the one with electric contacts can be used for position control. It does not require high environmental conditions, but the instrument time constant is large and the accuracy is not too high. Avoid using the first 1/3 of the scale, and it cannot be connected to recording and control instruments.
4. Bimetallic thermometer:
Bimetallic thermometer is suitable for measuring medium and low temperature on-site detection industrial instruments, and can be used to directly measure the temperature of gas, liquid, and steam. It has good linearity, slow response, low accuracy, and only makes on-site display. It cannot be connected to recording and control instruments. The one with electric contacts can be used for position control. Compared with industrial mercury thermometers, they have the advantages of no mercury harm, easy to read, strong and vibration-resistant, and can replace industrial glass mercury thermometers.
5. Glass thermometer:
Glass thermometers are generally used in the range of 0~300℃, divided into ordinary and precision types. Ordinary thermometers: use 1.5 or 1 level. Precision measurement thermometers: should use 0.5 or 0.25 level. Good linearity, general response, only for field display, no need to match other instruments, with electrical contacts can be used for position control. Simple structure, easy to use, low price, etc., but it is inconvenient for long-distance temperature measurement, fragile structure, fragile, not allowed to exceed the upper limit of the thermometer, and cannot be connected to recording and control instruments.