Briefly describe how a bourdon-tube pressure transmitter converts pressure into an electrical signal.

• A. Pressure deflects the curved bourdon tube, moving a linkage that drives a transducer to produce a 4-20 mA or voltage signal.
• B. Pressure changes the resistance of the bourdon tube, which is read by a bridge circuit.
• C. Pressure heats the bourdon tube, and the temperature change is converted to voltage.
• D. Pressure rotates a shaft that drives an encoder to produce digital signals.

Answer: (A)

The main idea is that a bourdon-tube pressure transmitter converts pressure into mechanical motion, which is then turned into an electrical signal. When pressure inside the curved bourdon tube increases, the tube tends to straighten. That small, precise displacement at the tube end is transmitted through a linkage to a transducer. The transducer then converts that mechanical movement into an electrical output, typically a current in a 4-20 mA loop or a corresponding voltage signal. This is why the bending and straightening of the curved tube, not any change in resistance or heating, is the fundamental sensing mechanism.

In other designs, you might see resistance changes or temperature-based methods, but those are not how bourdon-tube transmitters operate. And using a shaft and encoder would be for measuring rotation, not pressure. The essential concept is the mechanical deflection from pressurization, interpreted by a transducer to produce a usable electrical signal.