Process Control and Instrumentation
Temperature measurement range of iron-constantan thermocouple is 0 to 870°C. It can be used to measure sub zero temperature, because at lower temperature

Embrittlement of iron occurs
Rusting of iron takes place
Emf produced is very low of the order of microvolt
Both B and C Here

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Process Control and Instrumentation
Time constant is the

Same as dead time
Same as transportation lag
Time taken by the controlled variable to reach 63.2% of its full change
Time required by the measured variable to reach 63.2% of its ultimate change

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