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Multiple Choice Questions

Infrared Gas Analyzers Questions & Answers

Infrared Gas Analyzers Questions & Answers

1. Which of the following is not a detector used in mid Infrared Spectrophotometer?

a) Thermopile
b) Thermistor
c) Pyroelectric cell
d) Golay cell

Answer: d

Explanation: Golay cell is not used in mid Infrared Spectrophotometer. It is used in far infrared spectrometer.

2. Why is the use of infrared analyzers limited when it comes to the analysis of inorganic compounds?

a) Slow response occurs
b) Less accurate results occur
c) Strong absorption of IR radiation by water
d) Small range

Answer: c

Explanation: The use of infrared analyzers is limited when it comes to the analysis of inorganic compounds because of the strong absorption of IR radiation by water. It is particularly used for organic compounds.

3. Which of the following is the chopping frequency used for industrial analyzers in simple infrared analyser for gas analysis?

a) 2-10 Hz
b) 2-50 Hz
c) 2-100 Hz
d) 2-150 Hz

Answer: a

Explanation: The chopping frequency used for industrial analysers in simple infrared analyzer for gas analysis is 2-10 Hz. The chopper is motor driven.

4. Which of the following is used as a source in simple infrared analyzer for gas analysis?

a) Tungsten filament lamp
b) Nernst glower
c) Hot-wire spiral
d) Mercury arc lamp

Answer: c

Explanation: Hot-wire spiral is used as a source in simple infrared analyzer for gas analysis. Two sources are used.

5. Vibration excitation occurs only if the sample has hetero-atomic molecules.

a) True
b) False

Answer: a

Explanation: Vibration excitation occurs only if the sample has hetero-atomic molecules. Hence, infrared analyzers are not used for gases whose molecules are formed by two identical atoms.

6. Which of the following is the chopping frequency used for medical applications in simple infrared analyser for gas analysis?

a) 2-10 Hz
b) 2-50 Hz
c) 2-100 Hz
d) 2-150 Hz

Answer: b

Explanation: The chopping frequency used for medical applications in simple infrared analyser for gas analysis is 2-50 Hz. The chopper is motor driven.

7. The movement of diaphragm in simple infrared analyser for gas analysis results in which of the following?

a) Variable resistance
b) Variable inductance
c) Variable capacitance
d) Variable conductance

Answer: c

Explanation: The movement of diaphragm in simple infrared analyser for gas analysis results in variable capacitance. The diaphragm forms one plate of the capacitor.

8. Which of the following is not the drawback of conventional infrared analyzers used for gas analysis?

a) Cell is difficult to maintain
b) It is expensive to replace
c) Detector is vibration sensitive
d) Only one source is used

Answer: d

Explanation: Two sources are used in conventional infrared analyzers used for gas analysis. To
overcome the drawbacks an improved model was created.

9. Which of the following is used as detector in improved infrared analyzer used for gas analysis?

a) PbSe
b) MgCl2
c) ZnCl
d) CuCl2

Answer: a

Explanation: PbSe is used as detector in improved infrared analyzer used for gas analysis. It is a solid state detector.

10. In calibration of CO2 analyser, in order to establish zero calibration which of the following is used as sample?

a) Oxygen
b) Hydrogen
c) Inert gases
d) Nitrogen

Answer: c

Explanation: In calibration of CO2 analyser, in order to establish zero calibration inert gases are used as sample. Generally, room air is also used.

11. Which of the following is not the characteristics of Indium arsenide photovoltaic detector used in infrared analyzers for hydrocarbons?

a) It operates at ambient temperature
b) Has maximum detectivity at 3.4µm
c) Sensitivity increases at longer wavelength
d) It has no response to radiation of wavelength greater than 4µm

Answer: c

Explanation: The sensitivity of Indium arsenide photovoltaic detector decreases at longer wavelength. It is insensitive to radiation having wavelength greater than 4µm.

12. Luft detector cell which uses gas as detection mechanism is not vibration sensitive.

a) True
b) False

Answer: b

Explanation: Luft detector cell which uses gas as detection mechanism is vibration sensitive. It is also subject to cross-talk with other gases.

13. Which kind of filter is used in improved version of infrared gas analyzer at the output end?

a) Low pass filter
b) High pass filter
c) Narrow bandpass filter
d) Wide bandpass filter

Answer: c

Explanation: The filter is used in improved version of infrared gas analyzer at the output end is narrow bandpass filter. The bandpass characteristics are matched with the absorption spectra of the gas of interest.

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