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PRESSURE MEASUREMENT FEATURE


WHERE CAN MULTIVARIABLE TRANSMITTERS BE USED? Multivariable transmitters can be used to measure differential pressure flow in a variety of applications. One example of where they can be used is the standard volume flow value measurement of natural gas when filling or emptying underground storage caverns under high static pressure. Measurement of the gas flow during both filling and emptying must be as accurate as possible. To help take account of changes in temperature and pressure that can happen in this application, the density of the gas must also be factored in, with the measured value being specified as the standard volume flow of the natural gas. The inherent benefits of multivariable pressure transmitters also make them ideal for level measurement applications. Differential pressure transmitters have long been used for hydrostatic level measurement, offering a cost-effective and easy to install solution, especially in applications with difficult operating conditions or where high pressures or temperatures need to be factored in. Multivariable pressure transmitters are particularly ideal for handling changes in density and temperature that can affect the accuracy of a hydrostatic level


measurement. By recording the process pressure and temperature in addition to the differential pressure, changes in the density of the measured medium can be corrected, significantly improving the quality of the measurement. An example of where this can be useful is the measurement of the water level in a steam boiler drum. Changes in pressure result in a corresponding change in temperature, causing the density of steam and water in the boiler to change. For steam to keep flowing to the process, and to prevent overheating and damage to the boiler superheater, the water level must be accurately measured. These types of applications are ideal for multivariable transmitters, which can provide the necessary compensations for pressure and temperature that can then be factored into the level measurement.


IS IT TRUE TO SAY THAT MORE IS NOT ALWAYS BETTER? Absolutely – at least in cases where you want to be able to accurately


The reduction of


ongoing maintenance and enhanced functionality means that potential savings


from opting for a multivariable device can reach up to 30 to 40 per cent."


measure flow or level without the cost, complexity and potential errors associated with using multiple instruments. The benefits that multivariable transmitters can offer over separate devices make them a logical and cost- effective choice for measuring flow in applications characterised by high pressures and / or temperatures or large pipeline sizes. With the ability to simultaneously measure differential pressure, process temperature and process pressure and compensate for changes in density, multivariable transmitters can help to significantly


improve measurement accuracy, offering increased scope for enhanced process efficiency and cost savings.


WHERE CAN I FIND OUT MORE? For more information about the benefits of multivariable transmitters, call 0870 600 6122 or email enquiries.mp.uk@gb.abb.com ref. ‘Multivariable pressure’.


ABB www.abb.com/temperature


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INSTRUMENTATION | MAY 2018


25


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