Process Control and Instrumentation

241. Thermal conductivity measurement is used for the determination of

1. O₂ percentage in the flue gas
2. Specific gravity of petrofuels
3. Composition of an alloy
4. CO₂ percentage in the flue gas

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242. Thermal well made of _________ gives the fastest speed of response, while measuring temperature by thermocouples.

1. Steel
2. Vycor (a glass)
3. Nichrome
4. Inconel

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243. Thermal wells are used in the temperature measurement to

1. Guard against corrosive and oxidising action on thermocouple materials
2. Reduce measuring lag
3. Increase the fidelity
4. Increase the sensitivity

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244. Thermal wells used in temperature measurements should have

1. Very thick walls
2. Low emissivity
3. Polished surface
4. High transmissivity of radiation

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245. Thermistor, which has high temperature co-efficient of resistivity, is used as the sensing element in resistance thermometer. It is a/an

1. Insulator
2. Conductor
3. Solid semi-conductor
4. Liquid semi-conductor

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246. Thermistors are made of

1. Ultra pure metals
2. Metal oxides
3. Iron-copper alloys
4. Nickel-chromium alloys

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247. Thermistors are used in _________ devices.

1. Voltage measuring
2. Temperature measuring
3. Temperature compensating
4. Both (B) & (C)

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248. Thermistors which have a very high temperature co-efficient of resistivity belong to the class of solid called

1. Dielectrics
2. Insulators
3. Semi conductors
4. Conductors

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249. Thermocouple in a thermal well behaves as a true

1. First order system
2. Second order system (overdamped)
3. Multiple first order system
4. Second order system (underdamped)

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250. Thermocouple is suitable for measuring

1. Liquid temperatures only
2. Very high temperatures only
3. Very low temperatures only
4. Both high and low temperatures

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