Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-10-25

Ensure the insertion depth is sufficient, that the installation location is not within the measurement dead zone, and check for any issues with the protective sleeve before installation.

1) Thermocouples should be avoided from being installed in areas with strong magnetic fields; the terminal box must not come into contact with the container walls or pipe walls of the medium being measured, and the temperature at the terminal box should not exceed 100°C. 2) When measuring temperature in a flowing fluid, the heated end of the thermocouple should be positioned in the opposite direction to the fluid being measured, at the center of the pipe where the flow velocity is highest.

1) Thermocouples should be avoided from being installed in areas with strong magnetic fields; the terminal box must not come into contact with the container walls or pipe walls of the medium being measured, and the temperature at the terminal box should not exceed 100°C. 2) When measuring temperature in a flowing fluid, the heated end of the thermocouple should be positioned in the opposite direction to the fluid being measured, at the center of the pipe where the flow velocity is highest.

As a commonly used temperature measuring instrument, thermocouples play an important role in industrial production. In practice, we attach great importance to the accuracy of measurement results, hoping to avoid errors during application. These errors are determined by various factors, such as the selection of thermocouples ； Installation of thermocouples ； Thermocouples are used, etc. Today, let’s talk about the precautions for installing thermocouples. 　　1. When installing a thermocouple, it should be placed as close as possible to the temperature control point that is to be measured. To prevent heat from escaping along the thermocouple or to avoid the protective tube affecting the temperature being measured, the thermocouple should be immersed in the fluid being measured to a depth of at least 10 times its diameter. When measuring the temperature of a solid, the thermocouple should be in contact with or in close contact to the material. To minimize the heat conduction error, the temperature gradient near the joint should be reduced. 　　2. The temperature measurement point selected should be representative; for example, when measuring the temperature of the fluid in a pipe, the sensing end of the thermocouple should be located at the area with the highest flow velocity in the pipe. Generally, the end of the thermocouple protection tube should extend beyond the centerline of the flow velocity. 　　3. When using a thermocouple to measure the temperature of gas in a pipe, if the wall temperature of the pipe is significantly higher or lower, the thermocouple will absorb or emit heat to it, thereby significantly altering the temperature being measured. At this time, a radiation shield can be used to bring its temperature close to that of the gas, by employing a so-called shielded thermocouple. 　　4. Special attention must be paid to the use of compensation wires when in actual use. The compensation wire, which is usually connected between the instrument and the terminal box, has thermoelectric properties that are the same as or similar to those of the thermocouple used; when connected to the thermocouple, it does not generate a significant additional thermoelectric potential, nor does it affect the total thermoelectric potential of the thermocouple circuit. If ordinary wires are used in place of compensation wires, no compensation effect will be achieved, thereby reducing the accuracy of temperature measurement. Therefore, the user should pay attention when installing the wiring for the instrument: when connecting the compensation wire to the thermocouple, be sure not to reverse the polarity, otherwise the temperature measurement error will increase. 　　5. In actual measurements, if the measured values deviate significantly from the actual values, apart from improper installation of the thermocouple, it may also be due to oxidation of the thermocouple wire or defects such as pores in the solder joints at the measurement end of the thermocouple.

1. When installing a thermocouple, it should be placed as close as possible to the temperature control point that is to be measured. To prevent heat from escaping along the thermocouple or to avoid the protective tube affecting the temperature being measured, the thermocouple should be immersed in the fluid being measured to a depth of at least 10 times its diameter. When measuring the temperature of a solid, the thermocouple should be in contact with or in close contact to the material. To minimize the heat conduction error, the temperature gradient near the joint should be reduced. 　　2. The temperature measurement point selected should be representative; for example, when measuring the temperature of the fluid in a pipe, the sensing end of the thermocouple should be located at the area with the highest flow velocity in the pipe. Generally, the end of the thermocouple protection tube should extend beyond the centerline of the flow velocity. 　　3. When using a thermocouple to measure the temperature of gas in a pipe, if the wall temperature of the pipe is significantly higher or lower, the thermocouple will absorb or emit heat to it, thereby significantly altering the temperature being measured. At this time, a radiation shield can be used to bring its temperature close to that of the gas, by employing a so-called shielded thermocouple. 　　4. Special attention must be paid to the use of compensation wires when in actual use. The compensation wire, which is usually connected between the instrument and the terminal box, has thermoelectric properties that are the same as or similar to those of the thermocouple used; when connected to the thermocouple, it does not generate a significant additional thermoelectric potential, nor does it affect the total thermoelectric potential of the thermocouple circuit. If ordinary wires are used in place of compensation wires, no compensation effect will be achieved, thereby reducing the accuracy of temperature measurement. Therefore, the user should pay attention when installing the wiring for the instrument: when connecting the compensation wire to the thermocouple, be sure not to reverse the polarity, otherwise the temperature measurement error will increase. 　　5. In actual measurements, if the measured values deviate significantly from the actual values, apart from improper installation of the thermocouple, it may also be due to oxidation of the thermocouple wire or defects such as pores in the solder joints at the measurement end of the thermocouple.

1) Thermocouples should be avoided from being installed in areas with strong magnetic fields; the terminal box must not come into contact with the container walls or pipe walls of the medium being measured, and the temperature at the terminal box should not exceed 100°C. 2) When measuring temperature in a flowing fluid, the heated end of the thermocouple should be positioned in the opposite direction to the fluid being measured, at the center of the pipe where the flow velocity is highest.

1) Thermocouples should be avoided from being installed in areas with strong magnetic fields; the terminal box must not come into contact with the container walls or pipe walls of the medium being measured, and the temperature at the terminal box should not exceed 100°C. 2) When measuring temperature in a flowing fluid, the heated end of the thermocouple should be positioned in the opposite direction to the fluid being measured, at the center of the pipe where the flow velocity is highest.

1. When installing a thermocouple, it should be placed as close as possible to the temperature control point that is to be measured. To prevent heat from escaping along the thermocouple or to avoid the protective tube affecting the temperature being measured, the thermocouple should be immersed in the fluid being measured to a depth of at least 10 times its diameter. When measuring the temperature of a solid, the thermocouple should be in contact with or in close contact to the material. To minimize the heat conduction error, the temperature gradient near the joint should be reduced. 　　2. The temperature measurement point selected should be representative; for example, when measuring the temperature of the fluid in a pipe, the sensing end of the thermocouple should be located at the area with the highest flow velocity in the pipe. Generally, the end of the thermocouple protection tube should extend beyond the centerline of the flow velocity. 　　3. When using a thermocouple to measure the temperature of gas in a pipe, if the wall temperature of the pipe is significantly higher or lower, the thermocouple will absorb or emit heat to it, thereby significantly altering the temperature being measured. At this time, a radiation shield can be used to bring its temperature close to that of the gas, by employing a so-called shielded thermocouple. 　　4. Special attention must be paid to the use of compensation wires when in actual use. The compensation wire, which is usually connected between the instrument and the terminal box, has thermoelectric properties that are the same as or similar to those of the thermocouple used; when connected to the thermocouple, it does not generate a significant additional thermoelectric potential, nor does it affect the total thermoelectric potential of the thermocouple circuit. If ordinary wires are used in place of compensation wires, no compensation effect will be achieved, thereby reducing the accuracy of temperature measurement. Therefore, the user should pay attention when installing the wiring for the instrument: when connecting the compensation wire to the thermocouple, be sure not to reverse the polarity, otherwise the temperature measurement error will increase. 　　5. In actual measurements, if the measured values deviate significantly from the actual values, apart from improper installation of the thermocouple, it may also be due to oxidation of the thermocouple wire or defects such as pores in the solder joints at the measurement end of the thermocouple.

　1. When installing a thermocouple, it should be placed as close as possible to the temperature control point that is to be measured. To prevent heat from escaping along the thermocouple or to avoid the protective tube affecting the temperature being measured, the thermocouple should be immersed in the fluid being measured to a depth of at least 10 times its diameter. When measuring the temperature of a solid, the thermocouple should be in contact with or in close contact to the material. To minimize the heat conduction error, the temperature gradient near the joint should be reduced. 　　2. The temperature measurement point selected should be representative; for example, when measuring the temperature of the fluid in a pipe, the sensing end of the thermocouple should be located at the area with the highest flow velocity in the pipe. Generally, the end of the thermocouple protection tube should extend beyond the centerline of the flow velocity. 　　3. When using a thermocouple to measure the temperature of gas in a pipe, if the wall temperature of the pipe is significantly higher or lower, the thermocouple will absorb or emit heat to it, thereby significantly altering the temperature being measured. At this time, a radiation shield can be used to bring its temperature close to that of the gas, by employing a so-called shielded thermocouple. 　　4. Special attention must be paid to the use of compensation wires when in actual use. The compensation wire, which is usually connected between the instrument and the terminal box, has thermoelectric properties that are the same as or similar to those of the thermocouple used; when connected to the thermocouple, it does not generate a significant additional thermoelectric potential, nor does it affect the total thermoelectric potential of the thermocouple circuit. If ordinary wires are used in place of compensation wires, no compensation effect will be achieved, thereby reducing the accuracy of temperature measurement. Therefore, the user should pay attention when installing the wiring for the instrument: when connecting the compensation wire to the thermocouple, be sure not to reverse the polarity, otherwise the temperature measurement error will increase. 　　5. In actual measurements, if the measured values deviate significantly from the actual values, apart from improper installation of the thermocouple, it may also be due to oxidation of the thermocouple wire or defects such as pores in the solder joints at the measurement end of the thermocouple. . Previous article: Using