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

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

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Process Control and Instrumentation
Vapour actuated pressure spring thermometer does not require ambient temperature compensation. Ambient temperature compensation is provided in gas or liquid expansion pressure spring thermometer by

Making the volume of thermometer bulb as large as conveniently possible
Reducing the volume of the capillary to a minimum
Reducing the volume of the receiving element to a minimum
All of these

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