With a sealed vessel as the reference point, a sensing technology is then applied to the surface of the vessel whose electrical characteristic varies with changes in strain. There are many different approaches to this. One common method is the piezoresistive strain gauge. These embed a resistor, (whose value changes with respect to mechanical strain) into a material such as silicon, polysilicon, metal foil, or as sputtered metal onto a thin film. In order to maximize the output signal and reduce errors, the pressure sensor typically uses four resistors in the Wheatstone bridge configuration.
With today’s high levels of integration, it is not uncommon for your piezoresistive sensor to also include compensation circuitry, such as resistors, all on a single substrate (see below).
Other sensing technologies also make use of a component’s value variation when deformed. For example, capacitors vary in capacitance when placed under strain. Sometimes a change in an inductor’s inductance can be caused by a locally placed diaphragm that moves in reaction to pressure changes.
The piezoelectric effect is also a common pressure measuring technology. This makes use of the fact that some materials, such as quartz, generate a voltage dependent on applied pressure.
As a result of the massive advances in silicon manufacturing technology in recent years, some mechanical elements are being machined into silicon chips known as microelectromechanical systems or MEMS devices.
They mostly utilize the same physical properties of the electronic components already mentioned, but leverage some moving parts machined into the semiconductor material. Such devices rarely provide the sensing element’s output signal; instead they precondition the signal electronically before outputting it via a package pin.