What are the installation requirements and precautions for thermal resistors?

When installing the thermal resistor, attention should be paid to the accuracy of temperature measurement, safety and reliability, and easy maintenance, and it should not affect the operation of the equipment and production operations. To meet the above requirements, pay attention to the following points when selecting the installation location and insertion depth of the thermal resistor: 1. In order to ensure sufficient heat exchange between the measuring end of the thermal resistor and the measured medium, the measuring point position should be reasonably selected, and try to avoid installing the thermal resistor near the dead corners of valves, elbows, pipelines and equipment. 2. The thermal resistor with a protective sleeve has heat transfer and heat dissipation losses. In order to reduce measurement errors, thermocouples and thermal resistors should have sufficient insertion depth: 1) For thermal resistors that measure the temperature of pipeline fluids, their measuring ends should generally be inserted into the pipeline (vertical installation or inclined installation). If the pipe diameter of the measured fluid is 200 mm, the insertion depth of the thermal resistor should be 100 mm; what are the installation requirements and precautions of thermal resistors?

2) For the temperature measurement of high-temperature, high-pressure and high-speed fluids (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 can be shallowly inserted or a thermal sleeve thermal resistor can be used. The shallow insertion thermal resistor protective sleeve should be inserted into the main steam pipe to a depth of not less than 75 mm; the standard insertion depth of the thermal sleeve thermal resistor is 100 mm.

3) If the temperature of the flue gas in the flue needs to be measured, even if the flue diameter is 4 m, the insertion depth of the thermal resistor is 1 m.

4) When the insertion depth of the measuring element exceeds 1 m, it should be installed vertically as much as possible, or a support frame and protective sleeve should be installed.

Precautions for the installation of thermal resistors

1. The thermal resistor should be installed vertically on the horizontal or vertical pipe as much as possible. The thermal resistor should be installed with a protective sleeve to facilitate maintenance and replacement.

2. When measuring the temperature in the pipeline, the length of the element should be on the pipeline line (that is, the insertion depth of the protective tube should be half of the pipe diameter).

3. When installing the temperature moving coil meter, the opening size should be appropriate and the installation should be beautiful and generous.

4. Use high-temperature resistant cables or high-temperature resistant compensation wires in high-temperature areas.

5. Choose different measuring elements according to different temperatures. Generally, thermal resistors are selected when the measured temperature is less than 400℃.

6. The wiring should be reasonable and beautiful, and the needle indication should be correct.

Thermal resistors are not only widely used in industrial temperature measurement, but also made into standard reference instruments. However, due to its temperature measurement range, its application is subject to certain restrictions. The temperature measurement principle of thermal resistors is based on the characteristic that the resistance value of conductors or semiconductors changes with temperature. It has many advantages, and can also transmit electrical signals remotely, with high sensitivity, strong stability, good interchangeability and accuracy, but it requires power excitation and cannot measure temperature changes instantaneously. Industrial thermal resistors generally use Pt100, Pt10, Cu50, Cu100. The temperature measurement range of platinum thermal resistors is generally -200-800℃, and that of copper thermal resistors is -40 to 140℃. Thermal resistors are classified in the same way as thermocouples, but they do not require compensation wires and are cheaper than thermocouples.

There are many installation forms for platinum thermal resistors, including fixed thread installation, movable thread installation, fixed flange installation, movable flange installation, movable pipe joint installation, straight pipe joint installation, etc.

The biggest difference between the selection of thermal resistors and thermocouples is the choice of temperature range. Thermal resistors are temperature sensors for measuring low temperatures, generally measuring temperatures between -200 and 800°C, while thermocouples are temperature sensors for measuring medium and high temperatures, generally measuring temperatures between 400 and 1800°C. When choosing, if the measured temperature is around 200°C, you should choose a thermal resistor. If the measured temperature is 600°C, you should choose a K-type thermocouple. If the measured temperature is between 1200 and 1600°C, you should choose an S-type or B-type thermocouple.