Sensing technologies

Piezo-resistive silicon sensing technologies

There are various methods of measurement at the sensing diaphragm but the most popular is usually made by an integrated electronic circuit using four strain gauges in a Wheatstone bridge configuration. Examples include piezo resistive silicon and thin film silicon diaphragm technologies which can satisfy even critical high reliability applications such as SIL (Safety Integrated Level) or PL (Performance Level) requirements, for example SIL 2 or PL: d rated. Measurement redundancy can be provided within a single pressure sensor, for example by having two measurement points on the diaphragm with completely independent signal processing and output channels.

The thin-film and diffused piezo-resistive silicon pressure sensing technology is highly sensitive so produces minimal diaphragm deflection with low material strain, ensuring excellent dynamic performance. Highly adaptable and compact with robust and modular packaging, this provides a fully integrated high reliability sensor readily produced for a wide range of applications from low cost OEM production to high performance R&D and test. The technology is very accurate, compact and lightweight with excellent operational characteristics e.g overload, vibration, shock and acceleration resistance.

Product lines offer an extensive choice of cost effective proven solutions for markets ranging from industrial machinery, process and environmental systems to automotive, rail and aerospace.

Utilising thin-film Silicon or Steel or diffused silicon diaphragms, very high and lowe pressure ranges can be effectively measured using ranges of just a few mbar up to 4000 bar or more and suitable for media temperatures from -40 up to 200 degC. Gauge, absolute, vacuum and differential configurations are available and flush mount/open face diaphragms.

Pressure Transducers and Transmitters

Pressure transducers Typically the pressure sensing module is supplied with a threaded process connection with an internal pressure inlet/cavity to allow the media to reach the internal diaphragm assembly. An external (flush/open) diaphragm can also be provided without this inlet to suit (for example) hygienic, viscous or slurry applications where it is often located at the thread end face, dependant on the mechanical configuration required.

Signal conditioning electronics are also provided behind the diaphragm assembly within a compact rugged cylindrical housing to provide a robust “pressure transducer” or “pressure transmitter” for a wide variety of industrial applications. Signal conditioning provides a rationalized high level output, compensated for environmental errors such as temperature changes and protected against ambient electromagnetic field radiation. This can be provided using purely analogue circuitry, but digital based signal conditioning (for example ASICs) often provide a superior level of linearity and thermal compensation that substantially enhances sensor measurement performance.

A “pressure transducer” will usually provide an amplified high level voltage output (e.g. 0 to 10Vdc, 0 to 5Vdc, 1-5Vdc, 0.5 to 4.5Vdc) although some simply offer the basic or “raw” sensor wheatstone bridge output (typically 50 to 100mV FS) whilst a “pressure transmitter” will produce a current output (e.g. 4 – 20mA). The elevated zero point of the 4-20mA or 1-5Vdc signals enables cable breaks and instrument faults to be detected. An external power supply is usually required to provide a fixed excitation voltage typically from 5V up to 32V dependant upon configuration and application.

The amplified output pressure transducer is often adequate for short to medium distance transmission within industrial environments, whilst the pressure transmitter is more suitable for long distance signal transmission and also for operating environments with dense / significant electromagnetic fields as the 4-20mA signal produced has lower sensitivity to electrical interference and automatically compensates for cable resistance.