When a basic differential pressure transmitter is used for flow measurement, what happens to the output signal?

A basic differential pressure transmitter measures the difference in pressure between two points, which is crucial for flow measurement, especially across an orifice plate. As fluid flows through the orifice, a pressure drop occurs, creating a differential pressure between the upstream and downstream sides. This differential pressure correlates directly with the flow rate according to the principles of fluid dynamics, typically described by the Bernoulli equation.

As flow increases, the differential pressure increases, resulting in an increase in the output signal of the transmitter, which is usually given in terms of a standard output format like 4-20 mA. Similarly, as flow decreases, the differential pressure decreases, leading to a drop in the output signal. Therefore, the output signal of the transmitter varies directly with the flow rate, enabling operators to monitor and control processes effectively.

The other options do not accurately describe the relationship between flow measurement and the output signal of a differential pressure transmitter. The positioning of the low-pressure side, the signal relay to a final control element, and variations in air supply pressure do not reflect the fundamental principle of how the output signal responds to changes in flow.