Sea Technology

APR 2015

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www.sea-technology.com April 2015 / st 43 D ifferential pressure sensors measure the difference in pressure between two sides of the sensor. These con- nections are normally referred to as P1, or high side (Hi), and P2, or low side (Lo), with the output of the sensor as P1– P2. Differential pressure sensors are used to measure many properties, such as pressure drops across flters, fuid levels (by comparing the pressure above and below the liquid) or fow rate measurement (pressure drop across a restriction, such as an orifce plate). A gauge pressure sensor is merely a differential pressure sensor in which one side is open to the ambient atmosphere. Typical applications of these pressure sensors include process control and moni- toring, liquid level measurements, leak detection, bulk liquid inventory, steam and gas-powered tur- bines in power plants, natural gas well monitoring, chemical process control, oil and gas exploration and other original equipment manufacturer environments. Hazardous Locations Locations such as refneries, oil and gas wells, drilling platforms, pipelines, compression stations, coal and gas- fred power plants, and areas of paint and chemicals pro- ducing large quantities of fammable liquids and gases cre- ate a risk of leaks. In some cases, gas, ignitable vapor or dust are present constantly or for long periods of time. Other areas may contain dangerous concentrations of fammable substances during process upsets, equipment deterioration between maintenance periods or during an incident. Area classifcation is the process of determining the type and size of these hazardous areas. Area classifcations are segmented into zones per IEC standard: IEC 60079-10-1 and IEC 60079-10-2 (explosive dusts). Division Two or Zone Two. Gas, vapors or mist are pres- ent only under abnormal conditions (most often leaks under abnormal conditions). Division One or Zone One. Gas, vapors or mist are pres- ent, or expected to be present, for long periods of time un- der normal operating conditions. Zone Zero. Gas or vapors are constantly present. Typical examples are gasoline and paint storage tanks. Differential Pressure Transducers For Hazardous Locations Sensors Remotely Monitor Gas, Chemical Leaks By Karmjit Sidhu (Top) A wet/wet differential pressure sensor with 0.25-inch male NPT ports and a TURCK minifast connector. (Bottom) Pressure sen- sors with a single cell (the AST 5300 on left) and two cells (the AST 5400 on right). These are typical types of differential pres- sure sensors used in wide op- erating temperatures. d h Differential Pressure Sensor Packaging Differential pressure sensor packaging for hazardous locations is very important when it comes to media isola- tion, range of differential pressure measurement in common mode pressure, operating temperature and environment conditions. One traditional sensor package—oil-flled with very thin isolation diaphragms—has been used for many years; how- ever, with the introduction of modern materials and elec- tronics, oil-free packages are entering markets. Oil or liquid flling is used to isolate the sensing elements, either capaci- tive, piezo-resistive or inductive, from the media via a very

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