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There are three main types of orifice plate flowmeters. The D/2 types tap the pipe at 1 pipe diameter downstream. The quarter-circle and conical types tap at 2.5 and 8 times nominal pipe diameters, respectively. The D/2 types have higher coefficients of variation in fluid-flow and viscosity. This difference makes it difficult to select the most appropriate type of flowmeter for your needs.
The orifice plate is used in a wide range of applications. Its high flow-density capacity makes it useful for measuring water, chemical, and gas flows. Its vent holes are located on top of the liquids and prevent condensate from forming. It also prevents the formation of gas pockets. It is widely available. Listed below are the different types of orifice plate flowmeters.
Calibration
Calibration of orifice plate flow meters is essential for the accuracy of its readings. There are two primary elements in orifice plate flowmeters: an orifice plate and a pressure drop meter. The calibration process involves recording the flow rate against the pressure drop and then incorporating the actual flow coefficient, which includes density and beta ratio, into the equation. Using the data obtained from a test flow, a power law calibration model is generated.
Accuracy is the measure of the accuracy and precision of the flow rate. Accuracy is the closeness of the measurement to the true value. A flowmeter with a high accuracy will report a greater F value than one with lower accuracy. However, a simple calibration equation is not adequate to capture the behavior of nature over its entire flow range. Calibration must also include the transmitter and orifice plate. It should also include a certificate of accuracy at 1000 psi, 120 deg F, and flow coefficients.
Application
An orifice plate flowmeter can be used for a variety of fluid measurements. Although the accuracy of an orifice flowmeter is not always guaranteed, it is still possible to calculate its flow rate without calibration. For this purpose, you should check the construction and installation of the flowmeter with the relevant handbook or standard. The calculation of the flow rate takes into account the fluid properties, pipe diameter, orifice size, measured differential pressure, and the coefficient of discharge of the orifice plate. The orifice plate can be replaced to increase its accuracy.
The primary element of an orifice plate flowmeter is a plate with a hole concentric to the pipeline. This plate is also known as a differential pressure cell, which measures the flow rate by detecting the difference in pressure across the orifice. The differential pressure data is then fed to a flow computer or indicator. It also allows the user to compensate for variations in density of fluid in a given process.
