Introduction to the basic knowledge of 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 by 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 part. 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 technology 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 rate 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.　　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. However, the fouling of the pipeline will affect the accuracy.　　Vortex flowmeter 　　Vortex flowmeter is to place a non-streamlined vortex generator in the fluid. 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 flow meter has no moving parts or holes and can accurately measure the flow of gas. Thermal mass flowmeter 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. 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. It is highly accurate to measure conductive liquid when the tube is full. Electromagnetic flowmeters can be used to measure the flow rate of slurry fluids.　　 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 electric potential is proportional to the flow rate and is detected by 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 switching DC currents with alternating polarities.　　The measurement system consists of a transmitter and a sensor.　　 It has two models: 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).