Question

MSA methanometer works based on the principle of

• A. Formation of gas cap
• B. Wheatstone bridge
• C. Infra-red radiation
• D. Optical Properties

Hint:

There are two main types of electronic methanometers:
1. Catalytic: Burns methane and measures the resistance change with a Wheatstone bridge.
2. Infrared: Measures the absorption of specific wavelengths of infrared light by methane molecules.
The MSA brand is historically associated with the catalytic type.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the working principle of a specific type of methane detector, the MSA methanometer.

Step 2: Detailed Explanation:
The MSA methanometer is a well-known example of a

catalytic combustion or

pellistor-type gas detector.
Its working principle is as follows:
1. The sensor contains two small ceramic beads (pellistors).
One is an active detector filament coated with a catalyst (like platinum or palladium), and the other is an inert reference filament.
2. Both filaments are heated to a high temperature (around 500 \(^{\circ}\)C) and are arranged as two arms of a

Wheatstone bridge circuit.
3. When a methane-air mixture passes over the sensor, the methane oxidizes (burns) on the surface of the hot catalytic filament.
\[ CH_4 + 2O_2 \xrightarrow{\text{catalyst}} CO_2 + 2H_2O + \text{Heat} \] 4. This combustion releases heat, which further increases the temperature of the active filament.
5. The increase in temperature causes an increase in the filament's electrical resistance.
The reference filament's resistance remains unchanged as no combustion occurs on it.
6. This change in resistance unbalances the Wheatstone bridge, causing a current to flow through the galvanometer.
The magnitude of this current is proportional to the amount of methane burned, and the meter is calibrated to display the methane percentage directly.

Step 3: Final Answer:
The MSA methanometer works based on the principle of detecting a change in resistance using a Wheatstone bridge.
This corresponds to option (B).