DEFINE THE SENSITIVITY OF A PIEZOELECTRIC SENSING ELEMENT

Apiezoelectric sensoris a device that uses thepiezoelectric effect, to measure changes inpressure,acceleration,temperature,strain, orforceby converting them to anelectricalcharge. The prefixpiezo-is Greek for 'press' or 'squeeze'.
Charge mode pressure sensors generate a high-impedance charge output. ICP® (Integrated Circuit Piezoelectric) voltage mode-type sensors feature built-in microelectronic amplifiers, which convert the high-impedance charge into a low-impedance voltage output. (ICP is a registered trademark of PCB Piezotronics.)SENSOR CONSTRUCTIONPiezoelectric pressure sensors are available in various shapes and thread configurations to allow suitable mounting for various types of pressure measurements. Quartz crystals are used in most sensors to ensure stable, repeatable operation. The quartz crystals are usually preloaded in the housings to ensure good linearity. Tourmaline, another stable naturally piezoelectric crystal, is used in some PCB sensors where volumetric sensitivity is required.
CHARGE MODE SENSORS

When the crystal is stressed, a charge is generated. This high-impedance output must be routed through a special low-noise cable to an impedance-converting amplifier, such as a laboratory charge amplifier or source follower. High insulation resistance must be maintained in the cables and connections.

The primary function of the charge or voltage amplifier is to convert the high-impedance output to a usable low-impedance voltage signal for recording purposes. Laboratory charge amplifiers provide added versatility for signal normalization, ranging, and filtering. PCB's charge amplifiers have additional input adjustments for quasi-static measurements, static calibration, and drift-free dynamic operation. Miniature in-line amplifiers are generally of fixed range and frequency.

Charge mode quartz pressure sensors may be used at higher temperatures than ICP® sensors, since the temperature limitation is determined by the temperature limit of the crystals rather than built-in electronics.

When considering the use of charge mode systems, remember that the output from the crystals is a high impedance charge. The internal components of the pressure sensor and the external electrical connector maintain a very high (typically 10 e13ohm) insulation resistance. Consequently, any connectors, cables, or amplifiers used must also have a very high insulation resistance to maintain signal integrity.