MEMS and sensors

What is the principle of the NDIR gas sensor often used to measure indoor carbon dioxide (CO2) concentration?

  1. AIt weighs the CO2 directly
  2. BIt uses the fact that CO2 absorbs infrared light at a specific wavelength and finds the concentration from the amount of transmitted infrared
  3. CIt uses the fact that CO2 conducts electricity
Show answer and explanation

Answer: B. It uses the fact that CO2 absorbs infrared light at a specific wavelength and finds the concentration from the amount of transmitted infrared

The NDIR (non-dispersive infrared) method uses the strong absorption of infrared light at about 4.3 µm by CO2. A detector with a filter passing only that wavelength measures how much the infrared from the source weakens as it passes through the gas, giving the concentration. It is highly selective and used for ventilation control and similar purposes.

  • A. It does not weigh the gas directly.
  • B. Correct. CO2 concentration is found from infrared absorption.
  • C. It does not use electrical conduction by CO2.
Practice this topic Back to topic

More MEMS and sensors questions

  1. Which MEMS-fabricated ultrasonic elements are sometimes used in under-display fingerprint sensors in smartphones and in medical ultrasound?
  2. In surface micromachining, what problem occurs if a structural thin film such as polysilicon has large internal residual stress?
  3. In a MEMS electrostatic actuator, if the voltage between two parallel electrodes is doubled, by roughly what factor does the electrostatic attraction between them change? (Assume the gap is unchanged.)
  4. When choosing the measurement range of a MEMS accelerometer (for example, ±2 g versus ±16 g), which reasoning is correct?
  5. In a parallel-plate electrostatic actuator, what is the phenomenon called in which, as the voltage rises, the movable electrode suddenly snaps to the fixed electrode once it passes a certain position?