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Flow meters are devices used to gauge gas or fluid flowing through it. They're used in a variety of applications where measuring flow is needed to check for leaks, control pressure and even prevent asthma attacks in asthma patients. The devices are categorized based on driving systems with mechanical, ultrasonic, pressure and electromagnetic being a few examples. Let's look at how they work. Mechanical flow meters These are traditional devices which still continue to be used. Basic types use turbines or wheels inserted into pipes to measure velocity and calculate volumetric flow by using the area on the pipes they're located. Mechanical flow meters can be of various types with common examples being piston meters - which use rotating pistons -, gear meters - which use a pair or more than two gears rotating at right angles - and single jet meters - which use impellers to increase and decrease liquid flow. Ultrasonic flow meters Ultrasonic flow meters have several advantages over their mechanical counterparts. They can be used to measure all sorts of liquids - like molten sulfur, water and chemicals among others -as long as the speed of sound can be calculated. Since they don't use mechanical parts, maintenance of such devices is relatively low. They're also a lot more reliable than mechanical systems and are quicker to use since they don't have to be inserted inside a pipe but merely clamped to the outside. Doppler and transit are the two types of ultrasonic meters. Both use transducers to measure flow but in different ways. A Doppler factors in shift in frequency as disturbance in the liquid influences reflection. This shift is the same as the flow rate. On the other hand, transit meters have transducers transmitting signals through a volume of liquid from opposite sides. The difference in time between the two signals gives the flow rate. Pressure-based flow meters In pressure-based flow meters, differential pressure or dynamic pressure determines flow rate. Pitot tubes, cone meters and Dall tubes are a few examples of devices. When using differential pressure, the pipe is constricted to create a drop in pressure. The more liquid that's introduced, the more pressure is created. The flow rate is determined by taking the difference in upstream and downstream pressure values. Dynamic pressure is derived by measuring the difference between static (the pressure at a stagnation point) and stagnation pressure (the point where fluid viscosity is zero). Electromagnetic flow meters Electromagnetic meters, as is obvious, use magnetic fields to determine flow rate. As a magnetic field is created in a section of a pipe, changes in voltage are created by the fluid's conductive particles. This change is used to measure the velocity of the flow. Such meters are ideal for calculating certain water-based liquids like wastewater but aren't suitable for hydrocarbons, oil and distilled water. When selecting flow meters, a number of variables have to be considered. Since one type may not work on certain gases or liquids, choosing the wrong device is an expensive loss. Questions like what kind of liquid/gas is to measured, viscosity (in the case of non-water-based liquids) and amount of impurities must be answered. Piping is another factor where size, material, upstream/downstream turns and valves have to be decided. Lastly, determining how the flow rate should be presented, i.e., whether in volumetric units or mass, will influence the type of meter to be used. ltrasonic flow meter can easily withstand the roughest and most hazardous applications. Aquip Systems provides solutions for a real time concentration analysis with laboratory accuracy. Check out their website aquip.com.au for additional details.
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