Pressure Transducer

A pressure transducer is a device which converts an applied pressure into a measurable electrical signal.

A pressure transducer consists of two main parts, an elastic material which will deform when exposed to a pressurized medium and a electrical device which detects the deformation.

The elastic material can be formed into many different shapes and sizes depending on the sensing principle and range of pressures to be measured. The most common method of utilising the elastic material is to form it into a thin flexible membrane called a diaphragm. The electrical device which is combined with the diaphragm to create a pressure transducer can be based on a resistive, capacitive or inductive principle of operation.

A resistive pressure transducer has strain gauges bonded to the surface of the diaphragm so that any change in pressure will cause a change in the electrical resistance of each strain gauge.

A variable capacitance pressure transducer has a capacitive plate bonded to one side of the diaphragm and another capacitive plate bonded to an unpressurized surface in close proximty to the diaphragm. A change in pressure will widen or narrow the gap between the two plates which varies the capacitance.

An inductive pressure transducer uses the principle of inductance to convert the flexing of a diaphragm into the linear movement of a ferromagnetic core. The movement of the core is used to vary the induced current generated by an AC powered primary coil on another secondary pick-up coil.

Other types of pressure transducer utilise the principle of the piezo-electric effect, changing resonant frequency.

The pressure transducer sensing elements are mainly used by original equipment manufacturers (OEM) who incoporate them into their own products (e.g. gas analysers, leakage monitoring equipment) or pressure measurement manufacturers who incorporate them into more complex pressure sensors with compensated millivolt, amplified voltage, 4-20mA current loop or digital interface outputs, which are then sold to end users and equipment integrators.

More complex pressure transducers include an electronic circuit for rationalising the transducer output signal so that there is very little difference from one transducer to another of the same type. A temperature compensation circuit is also added to reduce the errors associated with changes in media temperature. Often the rationalised and compensated output is then converted to a standardised output signal to make it universally compatible with end users instrumentation such as readouts, analog to digital converter cards, programmable logic controllers and data acquisition cards.

Pressure transducers are fitted with a mechanical process connector (e.g. 1/4 BSP male, 1/2 NPT male) to the front of the diaphragm, and an electrical interface connection (e.g. DIN plug, M12) on the back of the electronics housing to enable the user to easily install the pressure transducer. In the case of pressure transducers sensing elements used by pressure measurement equipment manufacturers and OEMs, the pressure transducers may only have a prepared surface for clamping, bonding or welding and a PCB with pads or pin-holes suitable for soldering.



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