2. Force balance sensors and transmitters

The principle consists in simultaneously applying a pressure force and an equal, counter-reactive force to a measuring element, so as to maintain this element in permanent equilibrium (as in a manometric balance). To this end, an angular displacement sensor translates the pressure force into the input signal of a control loop. At the output of this loop, the energy required to return the scale to its initial position is converted into a measurement of the pressure force. This has a number of advantages:

• the measuring element is virtually static, reducing fatigue, wear and hysteresis;

• the change in pressure chamber volume is practically zero;

• The opposing force is usually produced by an electric current that is easy to measure, transmit and use;

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