Reradiation of heat from

Heater temperatures measured with a static thermocouple will read low. This is because of the reradiation of heat from the thermocouple. The higher the temperature, the greater the error. For example, the flue gas temperature to the convective section, measured by a static thermocouple, may read 100 F-200 F lower than the real temperature. A velocity thermocouple will correct this problem. The velocity thermocouple device channels hot flue gas past an ordinary thermocouple. This largely eliminates the error due to reradiation. 

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