3.2. Force and Deformation Sensors

3.2. Force and Deformation Sensors

Among the range of mechanical sensors (position, speed, acceleration, shock, among others), we propose discussing two typical examples, one passive, the other active, whose measurands are forces and deformations.

Passive sensors are mostly used in mechanics. In Chapter 2, we saw that these sensors can be resistive, capacitive or inductive. Inductive sensors are often used for displacement measurements. On the other hand, resistive sensors are often used for deformation measurements and are sometimes called, somewhat incorrectly, constraint gauges.

The piezoelectric effect [CAD 64] is the most widely used basic principle in active mechanical sensors. It is used in its simplest form with force and deformation sensors. In the following sections, we will explain the principles of piezoelectricity and some methods used to analyze the signals it generates.

It is important to remember that very little difference exists between force and constraint measurements. In order to measure a force, a kind of dynamometer is generally used. This is a tool that helps us establish an equilibrium between the force we want to measure and the constraint produced by the deformations undergone by a solid that makes up a part of the sensor under the action of this force. Working in the elastic domain of deformations, we see that constraints and deformations are proportional. A simple calibration allows the same sensor to carry out both a constraint measurement (or force by surface unit) and a deformation measurement.