The sensing element of a thermocouple at its hot junction is provided...
The sensitive element is required to measure its temperature change due to radiant energy received relative to the temperature of the immediate surroundings.
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The sensing element of a thermocouple at its hot junction is provided...
Explanation:
The principal reason for giving a shield to the sensing element of a thermocouple at its hot junction while taking measurements in a high-temperature gas is to reduce radiation error. Let's understand this in detail:
Thermocouples:
Thermocouples are temperature sensors that consist of two different metal wires joined together at one end, known as the hot junction. When there is a temperature difference between the hot junction and the other end, known as the cold junction, a voltage is generated. This voltage is known as the Seebeck voltage and is used to measure the temperature.
High-Temperature Gas:
When measuring the temperature of a high-temperature gas, there are several factors that can cause errors in the measurement. These factors include conduction, convection, and radiation.
Radiation Error:
Radiation is the transfer of heat through electromagnetic waves. In high-temperature environments, such as a high-temperature gas, there is a significant amount of radiation present. This radiation can affect the accuracy of the temperature measurement by introducing errors in the Seebeck voltage.
Shielding:
To reduce the radiation error, a shield is provided to the sensing element at its hot junction. The shield acts as a barrier, preventing the radiation from directly reaching the thermocouple. By shielding the sensing element, the accuracy of the temperature measurement is improved as the radiation error is minimized.
Other Factors:
While conduction and convection errors can also affect the temperature measurement, the principal reason for providing a shield is to reduce radiation error. Conduction is the transfer of heat through direct contact, and convection is the transfer of heat through the movement of fluids. Although these factors can introduce errors in the measurement, they are not the main concern when measuring temperature in a high-temperature gas.
Conclusion:
In conclusion, the principal reason for giving a shield to the sensing element of a thermocouple at its hot junction while taking measurements in a high-temperature gas is to reduce radiation error. The shield acts as a barrier, minimizing the impact of radiation on the accuracy of the temperature measurement.