Pressure measurement


As a designer and manufacturer of measurement sensor components and a distribution partner for other leading sensor suppliers, Variohm EuroSensor offers a comprehensive range of pressure transducers that find widespread use for measurement and monitoring tasks throughout industry.


P


ressure transducers, also known as pressure sensors or pressure transmitters, accurately sense pressure in gases and


liquids and output the value as an analogue or digital signal in real time. The pressure, measured as the applied force by a fluid (liquid or gas) on a surface area, can be either an absolute value referenced to zero pressure, or a gauge value relative to ambient pressure, or a differential value between two independent pressure sources. Normally measured in units and sub- units of a bar, the output values can be a positive or a negative vacuum pressure. Using the latest technology sensing and electronics elements, Variohm utilise three main methods of building pressure transducers which are all piezo resistive approaches. The most used technology for its product range is a resistive bridge printed onto a steel membrane with thin film measuring cells that are fully sealed in hermitically welded housings with no O-rings. These products provide excellent performance characteristics in terms of stability, sensitivity, performance over temperature and handling of higher frequency applications.


The second technology has similar design


characteristics but with an methodology where resistors are bonded onto the pressure transmitter membrane. This affords more freedom in the selection of the material for wetted parts and can therefore be used on applications that demand more stringent media compatibility requirements. The third technology Variohm employs is based around a silicon chip which


measures the applied pressure. This technology is the least robust against media and pressure peaks as it has internal O-Rings. However, due to the higher integration of the chip on the sensor’s PCB the cost of this technology allows more cost- effective products if the application is suitable. A wide choice of industry compatible voltage


or current outputs are available, as well as signal output options such as CANopen, J1939 (SAE- J1939) and HART. The same technology can also be employed as part of a pressure switch that will trigger a relay output when a pre-set pressure level is reached. Variohm’s comprehensive product portfolio


spans absolute, gauge and differential pressure measurement in several pressure range variants from a few millibars up to 5000 bar. The selection of the correct pressure range is the most important factor when specifying a suitable sensor and Variohm recommends roughly 50 to 75 per cent of the sensors’ overall pressure range. A sensor with a much wider pressure range than required would cause accuracy problems whilst using a pressure sensor with a range too close to maximum could cause the burst pressure (overpressure) to be exceeded, resulting in sensor damage. The accuracy of Variohm’s pressure transducers is typically between one per cent and 0.15 per cent depending on the selected model for the application. The widely specified EPT series, developed and


improved over several years, is well proven in automotive and mobile machinery, industrial hydraulics, refrigeration, off-road construction and agricultural applications. A recent development for the range is the new


EPT31H2 pressure transducer which has EC79 approval for use with hydrogen processes up to 700 bar with a full range to 1,000 bar. The EPT range also includes miniature versions for space restricted applications, low power consumption versions for remote battery operated equipment, and versions that include SIL 2, PL:d safety compliant options. Variohm pressure sensors are characterised by


high strength, ruggedised designs with housings and wetted parts suited to the potentially corrosive properties of the measured gases and liquids. Most often used materials across the range are various grades of stainless steels although thermoplastics, brass, and more exotic housing and wetted parts materials such as titanium are also available. The comprehensive range includes miniature designs and a wide choice of pressure port configurations and electrical interfacing options for maximum application flexibility. Environmental ratings from IP65 to IP69K ensure high resistance to debris and water ingress. Variohm also offers combined pressure and temperature transducers that enable a single device to take measurements of both variables, saving valuable space and simplifying system controls. Applications range from level and flow


measurement for filtration processes in the beverage industries to monitoring pressure levels on medical devices such as ventilators. Pressure sensors are commonly used for system safety in oil and gas extraction and precise control in mobile hydraulics. Amongst the most demanding environments, and a true proving ground for Variohm over several years in the business, is that of vehicle technology and in particular the world of motorsports. One of many applications in this area is for vehicle brake pressure monitoring where typical shock levels are specified to 1,000 g and vibration to 16 g peak (20 to 2,000 Hz). Variohm EuroSensor works closely with its customers in all industries on an engineer-to- engineer basis, providing a specialist technical support service with stock delivery available across a wide range of field-proven sensors - and complete aftersales support. To address the ever-changing need for increased


Piezo resistive pressure transducers


precision, faster measurement and improved durability, the Towcester-UK based designer manufactures and sources a comprehensive range of sensor technologies for linear and rotary position, load, force, vibration and temperature measurement in demanding applications throughout industry, agriculture, construction, autosports, aerospace and research.


Variohm EuroSensor www.variohm.com 42


May 2021 Instrumentation Monthly


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