Which statement is true about constant temperature and calorimetric sensors?

• A. They are types of mass flow sensors.
• B. They measure velocity.
• C. They measure volume.
• D. They are not used for flow.

Answer: (A)

Constant temperature and calorimetric sensors are thermal flow sensors that determine how much mass is moving with the fluid. In a constant-temperature device, a heated element is kept at a fixed temperature, and the control system adjusts the electrical power to maintain that temperature. The power needed grows with higher mass flow because more fluid carries away heat. That power level becomes the output signal and is proportional to mass flow rate. In a calorimetric sensor, the rate of heat transfer to or from the fluid is measured directly; again, higher mass flow changes the heat transfer or temperature response in a way that tracks mass flow. So these sensors specifically measure how much mass passes per unit time, not velocity or volume. They are indeed used for flow measurement. The other statements don’t fit because velocity and volume are not the primary quantities these sensors output, and they are not about flow at all would be incorrect.