Making sense of sensors
September 1st 2011

Graham Pattison, sales director of Variohm EuroSensor, explains some of the different types of pressure sensors and their applications

Pressure transducers characterised by tubular design with threaded mounting at one end and electrical connector at the other, are one of the most widely used sensor types for industrial gas and liquid pressure measurement. For example, Variohm EuroSensor's EPT series is available in a variety of housing options with a choice of power input and output signals, and is available in pressure ranges from 0 to 0.25 and up to 4000 bar, this industry standard design employs a tried and tested semiconductor thin-film pressure measuring cell encased in 304 grade stainless steel with accuracy better than ±0.8% and stability below ±0.1%.

The diaphragm is hermetically welded and with no internal liquid or O-rings, the dry cell design guarantees safe and reliable operation. These pressure transducer types are available for general purpose use or easily customised with different materials or sensor heads for highly specified instrumentation and control applications across pneumatics, hydraulics, process control, HVAC, water management, transport machinery, automotive and many other industries.

For flexibility, Variohm's EPT range offers both imperial and metric mechanical port configuration from 1/4in to M14 and a choice of cabled or connector electrical interfaces including EN 175301-803 (DIN43650) and Metri-Pack. Industry standard 22mm case diameters with hexagonal nut fixing are available along with miniature 12 or 15mm diameter versions.

Even for standard use, pressure measurement requires a robust design with generous over range pressure and burst pressure ratings. These transducers have nominal 2x and 5x overload and burst pressure ratings with higher factors available in customised versions. Similarly, environmental specifications need to match the often harsh industrial pressure measurement conditions – temperature ranges are from -40 to +125°C, with nominal shock and vibration ratings of 1000g (11ms, 1/2 sine) and 16g peak (20 to 2000 Hz). Life ratings are in excess of 10 million operations and sealing conforms to IP66.

To meet the demands of the widest range of applications, power input or excitation requirements are a choice or 5 or 10-32 VDC with reverse voltage protection. A choice of output signal types includes 0.5 - 4.5 VDC, 1 - 5 VDC, 0 - 10 VDC and 4 -20 mA.

Variohm EuroSensor supplies application customised versions of the EPT range for areas such as brake pressure monitoring on railways and cranes where customer demands push the standard specifications to the limit and beyond.

These applications require a focussed approach in both development and manufacture to meet and exceed the environmental conditions with no compromise in quality and no room for failure.

These transducers include elevated speciation levels to EN 61373 and DIN EN60068-2-27 for shock and vibration and EMC sensitivity protection to EN50155 and EN50121. Furthermore, fire grade protection to class UL94 and environmental ratings to IP69K with dielectric strength of over 700 VDC for one minute is required. Using advanced FIT rate analysis, a MTBF life of over 480 years was determined for one particular application.

Variohm also has a wide range of other pressure sensing products including a new combined pressure and temperature sensor as part of the EPT pressure transducer range as well as pressure switches and dedicated HVAC sensors which may offer a lower cost solution for refrigeration, automotive and other demanding markets. A new range of very low cost sensors with the same cylindrical style has recently been launched that feature a piezoresistive ratiometric output measuring cell in a lightweight and durable injection moulded ABS plastic housing for pressure ranges to 20 bar.

Also available are bi-directional pressure transducers that suit customisation for range and output signals as well as a range of aerospace test, food and pharmaceutical pressure measurement sensors in a wide variety of housings, materials and pressure port styles including flush diaphragm types.

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