Certified Pulmonary Function Technologist (CPFT) Practice Exam

Which thermal tachometer is specifically used in a helium gas analyzer?

1. Piezoresistive sensor

2. Thermocouple

3. Wheatstone bridge

4. Capacitance sensor

The correct answer is: Wheatstone bridge

In the context of helium gas analysis, the Wheatstone bridge is particularly significant because it measures changes in resistance that occur in response to temperature fluctuations, which is a crucial function in a thermal tachometer. When helium gas flows through a thermal sensor, it affects the temperature of that sensor. The Wheatstone bridge configuration can detect these temperature changes by measuring the resulting resistance variations, thus providing accurate flow measurements of the helium. The other options serve different roles or principles. Piezoresistive sensors are more commonly used for pressure measurement rather than gas flow or composition. Thermocouples measure temperature directly, while capacitance sensors measure changes in capacitance but are not specifically optimized for flow measurement in the way that a Wheatstone bridge is designed to analyze resistance changes related to thermal flow characteristics in a gas like helium. Therefore, the Wheatstone bridge's functionality aligns best with the requirements of helium gas analysis, making it the appropriate choice in this scenario.