The use of pressure transducers

The pressure transducers are tools that allow to measure the strength of a gas or a liquid, by converting into an electrical signal the value obtained. Generally miniature pressure sensors consist of a diaphragm which is sensitive with respect to pressure variations, and a strain gauge, that is a component that can be pulled or pushed by the diaphragm. There are three types of electrical power that can be measured: 4-20 mA, voltage and millivolts. The control of pressure systems represents the typical mode of use of these instruments, which can be used to monitor the pressure of a boiler. A normalized signal can be used as an output, which means that pressure transducers can be connected to any type of regulation system: this is why the possible applications are potentially infinite.

What are transducers for?

In regulation systems, the physical size of the pressure can appear as absolute pressure, in the form of relative pressure or in the form of differential pressure. To be able to identify the type of pressure you are dealing with, you need to be aware of the reference point. In particular, absolute pressure uses vacuum as a reference point: in other words, there is no pressure. With the differential pressure, on the other hand, the difference in pressure between two systems is indicated, which are connected to the two connections of the pressure transducer: essentially, one of the two systems corresponds to the reference point. As for relative pressure finally, the point of reference is environmental pressure. In the pressure measurement, sensors with different measurement principles can be used, which affect the accuracy, the reaction speed and other parameters.

Pressure measurement

The measurement principles used when using pressure transducers can be different. The thin-film sensors, for example, are based on the same principle that characterizes the strain gauges: the latter correspond to resistive structures lattice that can be compressed or stretched giving rise to a resistance variation caused by variations in thickness and induced length which can be measured. Relying on a Wheatstone bridge, four resistances are placed on a membrane, so that it is possible to detect the deformation to which the same membrane goes when it is subjected to a pressure.

The thick film sensors, in turn, are based on four elements used to create a Wheatstone bridge. In this case we are dealing with resistive structures that are printed on a ceramic base or on another basic element: this is possible thanks to the thick film technology, which precedes a high temperature treatment. The geometric variation that is determined by the compression and stretching of the material induces the variation of the resistance of the bridge. A third possibility is represented by piezoresistive sensors, which use a semiconductor measuring diaphragm.