Differential pressure

The difference between 2 absolute pressures p1 and p2 is called differential pressure Δp. It is often used in technical applications for control purposes.

How does a differential pressure sensor work?

A differential pressure sensor has two process connections. The pressures act in opposite directions on the membrane. The measurement result is always the difference between the two pressures p2 – p1 = Δp.

Fig. 1: Schematic diagramm differential pressure sensor

Where is diffential pressure measurement applied?

Example of filter monitoring:

In ventilation systems, the differential pressure can be used to determine the degree of contamination in a filter when the pressures are measured in front of and behind the filter. The more contaminated the filter element is, the more resistance there is against the medium flowing through it.

Example of flow rate measurement:

A common application of differential pressure is flow rate measurement in pipes. This differential pressure method requires a primary element to be installed in the pipe. Primary elements are available in various designs and taper the pipe cross-section at the measuring point. This results in a local increase in the flow velocity at the point of constriction, which in turn results in a change to the static pressure (p1 stat and p2 stat). The pressure connections for measurements are located directly in front of and behind the primary element. The pressure difference is an indirect measure of the flow.

Fig. 2: Flow rate measurement using a venturi and differential static pressure values