Differential pressure measurement is largely used in domestic and industrial applications. It is often the basis of other measurements such as flow, level, density, viscosity and even temperature. The most common being level and flow. DP Flow rate measurement is one of the most common applications for differential pressure transmitters. By measuring the difference in fluid pressure while the fluid flows through a pipe it is possible to calculate the flow rate. Differential pressure flow meters have a primary and a secondary element. Generally speaking , the primary element is designed to produce a difference in pressure as the flow increases. There are many different types of primary element, the most common being the orifice plate, venturi, flow nozzle and pitot tube. The secondary element of the flow meter is the differential pressure transmitter. It is designed to measure the differential pressure produced by the primary element as accurately as possible. In particular it is important that the differential pressure measurement is not affected by changes in the fluid pressure, temperature or other properties such as ambient temperature. A good dp transmitter will ensure that the differential pressure is measured accurately independent of other changing parameters and will reliably transmit a signal to represent the differential pressure. In the case of a dp flow transmitter the output signal may also include square root extraction. Although it is common these days for this function to be carried our in a flow computer of Dcs system. The output signal from and industrial DP transmitter is likely to be 4-20mA, but it may also include digital communications such as HART, Profibusm Fieldbus, Modbus 485 RTU or one of many other communication protocols. The objective being to provide an electrical signal for transmission to a remote process control instrument.