How Does a Piezoelectric Pressure Sensor Measure?

The basic measurement principle of piezoelectric sensors is simple. The crystals are placed in the sensor directly behind a thin membrane. This membrane then converts the pressure into a force onto the crystal, which then linearly reacts with a charge displacement, thus an electrical charge on the surface. This is a direct physical conversion of pressure into an electrical signal and as a result does not require any further sensor bridges, temperature compensation, etc. like other similar technology. Another advantage is that the thin membrane is protected by a high strength sensor element and, as a result, is extremely durable and has a high overload capacity. Since the piezoelectric effect is a microscopic property of the crystal lattice, the sensor has outstanding response behavior and is particularly suitable for fast, dynamic pressure sensing and for measurement with a high base load. Thus, for example, a base load of 500 bar can still be converted to mbar.

The crystal element charge is converted into an electrical signal by a charge amplifier or charge converter. In order to ensure a stable signal, piezoelectric pressure sensors are usually equipped with a high-pass filter, which is why this technology is only minimally suitable for static measurement and only used for dynamic pressure measurement. For use in these applications however, they have incomparable advantages and open up numerous possibilities, which would not be available using other technology.

A piezoelectric sensor is at the beginning of the measuring chain, which is followed by an external charge amplifier. The connection between the sensor and the charge amplifier must be transmitted using a special low-noise cable. The sensor discharges in the pico-coulombs, which is why the cable must be well protected and be specifically constructed for the prevention of triboelectric effects.

The PC output signal is converted into measurable 0-10V voltage in the charge amplifier. This voltage can then be passed on through a standard cable. The data acquisition system is the last step in the measuring chain. This is not absolutely mandatory, but is used in most applications. Because piezoelectric sensors are usually used in fast pressure cycles in the kHz range, suitable data recording with high sampling rates is necessary.

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