Basic knowledge of several commonly used flow meters
Basic knowledge of several commonly used flow meters
Flow measurement is one of the four important process parameters (the others are temperature, pressure and level). Closed pipe flow meters are classified according to the technologies they use, as follows: Differential pressure flow meters (DP) This is the most common flow technology, including orifice, venturi and sonic nozzle. DP flow meters can be used to measure the flow rates of most liquids, gases and steam. DP flowmeter has no moving parts, and flow measurement is one of the four important process parameters (the others are temperature, pressure and level). Closed pipe flow meters are classified by the technologies they use, as follows: Differential Pressure Flowmeter (DP) This is the most common flow technology, including orifice, venturi and sonic nozzle. DP flow meters can be used to measure the flow rates of most liquids, gases and steam. DP flowmeter has no moving parts, is widely used and easy to use. But after clogging, it will produce pressure loss and affect accuracy. The accuracy of flow measurement depends on the accuracy of the pressure gauge. volumetric flowmeter (PD) PD flowmeter is used to measure the volumetric flow rate of liquid or gas. It introduces fluid into the measuring space and calculates the number of rotations. Impellers, gears, pistons or orifices are used to divert fluids. The accuracy of the PD flowmeter is high, and it is one of several methods for measuring viscous liquids. But it will also produce unrecoverable pressure errors and require moving parts. Turbine flowmeter When fluid flows through the turbine flowmeter, the fluid causes the rotor to rotate. The rotation speed of the rotor is related to the speed of the fluid. The average flow rate of the fluid felt by the rotor is used to deduce the flow or total amount. Turbine flowmeter can accurately measure clean liquids and gases. Like PD flowmeters, turbine flowmeters also produce unrecoverable pressure errors and require moving parts. Electromagnetic flowmeter When a conductive fluid flows through an electromagnetic field, the velocity of the fluid can be obtained by measuring the voltage. The electromagnetic flowmeter has no moving parts and is not affected by the fluid. When the tube is full, the measurement accuracy of conductive liquid is very high. Electromagnetic flowmeters can be used to measure the flow rate of slurry fluids. Ultrasonic flowmeter The propagation time method and the Doppler effect method are commonly used methods for ultrasonic flowmeters to measure the average velocity of the fluid. Like other speed meters, it is a meter that measures volume flow. It is an unobstructed flow meter. If the ultrasonic transmitter is installed outside the pipeline for measurement, there is no need to insert it. It is suitable for almost all liquids, including slurries, with high accuracy. But the fouling of the pipeline will affect the accuracy. Vortex flowmeter Vortex flowmeter is to place a non-streamline vortex generator in the fluid, and the velocity of the vortex is proportional to the velocity of the fluid to calculate the volume flow. The vortex flowmeter is suitable for measuring liquid, gas or steam. It has no moving parts and no dirt problems. Vortex flowmeters will generate noise and require fluids with a higher flow rate to generate vortices. 'Thermal mass flow meter' measures the fluid velocity by measuring the increase in the temperature of the fluid or the decrease in the thermal sensor. The thermal mass flowmeter has no moving parts or holes and can accurately measure the flow of gas. Thermal mass flow meter is one of the few technologies that can measure mass flow, and it is also one of the few technologies used to measure large-caliber gas flow. Coriolis flowmeter This kind of flowmeter uses a vibrating fluid tube to produce a deflection corresponding to the mass flow rate for measurement. Coriolis flow meters can be used to measure the mass flow of liquid, slurry, gas or steam. High accuracy. However, regular maintenance should be carried out on the pipe wall to prevent corrosion. Electromagnetic flowmeter Measurement principle: Faraday’s law of electromagnetic induction proves that a conductor moving in a magnetic field will induce an electric potential. Using the principle of electromagnetic measurement, the fluid is a conductor in motion. The induced potential is proportional to the flow velocity and is detected by the two measuring electrodes. Then the transmitter amplifies it and calculates the flow rate based on the cross-sectional area of u200bu200bthe pipe. The constant magnetic field is generated by the switching DC current with alternating polarity. The measurement system consists of a transmitter and a sensor. It has two types: the integrated type, the transmitter and sensor form an integral mechanical unit; the separate type, the transmitter and sensor are installed separately. Transmitter: Promag50 (operated by buttons, two-line display) Sensor: PromagW (DN25……2000)
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