Pressure Sensor

a measuring converter of the pressure of a liquid or gas into electric, pneumatic, and other kinds of output signal; also used for measuring rarefaction and pressure drops.

For pressures up to 10 meganewtons per sq m (MN/mv²), or 100 kilograms-force per sq cm (kgf/cm²), and higher, pressure sensors are made on the principle of direct conversion of the measured pressure into stress and then into an output electrical signal—for example, piezoelectric and magneticelastic sensors. For measuring comparatively small pressures, pressure sensors are made with intermediate transducers (pressure stress → displacement) and terminal transducers (stress → measurement of electrical parameter). The intermediate types include liquid manometric transducers, springs, membranes, and bellows; among the terminal types are rheostatic, inductive, and capacitive transducers.

Pressure sensors operating on the principle of electrical or pneumatic force compensation also exist. The stress P(see Figure 1) created by the pressure being measured at the sensing element (1) is balanced by a reverse force device (3) through a system of levers (2). When measuring pressure, the controlling element (4) of the error indicator (5) is shifted from its original zero position. The error signal thus originating at the indicator (5) is amplified by the amplifier (6) and then passes as output current i_out, (or pressure P_out) to device (3) and the readout device (7). The output signal is changed until the counterforce developed in device (3) balances the measured pressure. At the moment of equilibrium, elements (2) and (4) return to their original positions. P_fiis the pressure in the feeder lines.

Figure 1. Schematic diagram of a pressure sensor of the compensation type: (a) electrical force compensation type, (b) pneumatic force compensation type

Pressure drops are measured by a differential membrane, bellows, or liquid manometric sensor.