The basic knowledge and comparison of several common flowmeter
Flow measurement is one of four major process parameters (the other three are the temperature, pressure and level). Closed pipe flowmeters are classified by the technology it used, for example:
Differential Pressure Flowmeter
This is the most common flow technology, including orifice plate, Venturi tube and sonic nozzle. DP flowmeters are used to measure the flow rate of most liquids, gases and vapors. DP flowmeters have no moving parts, with widely application, and easy to use. But if blocked, a pressure loss would affect the accuracy. Flow measurement accuracy depends on the accuracy of the pressure gauge.
PD flowmeter is used to measure the volumetric flow rate of liquid or gas. It brings the fluid into the metering space, and calculate the number of rotations. Impeller, gear, piston or orifice plate are used to shunt fluid. PD flowmeter is with high accuracy, and it is one of several methods for measuring viscous liquid. But it will also generate unrecoverable pressure error, and need to equip moving parts.
When the fluid flows through the turbine flowmeter, the fluid rotate the rotor. The rotational speed of the rotor is related to the speed of the fluid. Derive the flow rate or total flow by the average flow rate of fluid. Turbine flowmeter can accurately measure clean liquids and gases. Like PD flowmeter, turbine flowmeter will also generate unrecoverable pressure error, and need to equip moving parts.
When conducting fluid flows through the electromagnetic field, it can be obtain the fluid rate by measuring the voltage. Electromagnetic flowmeters have no moving parts, and are not influenced by the fluid. When full bore, the measurement accuracy of the conducting fluid is high. Electromagnetic flowmeters can be used to measure the flow rate of pulp fluid.
Propagation time method and the Doppler effect method are often used for ultrasonic flowmeter to measure the average fluid rate. Like other speed meters, it is a meter to measure the volume flow rate. It is a unimpeded flow meter, if the ultrasonic transmitter is mounted outside the pipe, no need to be inserted. It is suitable for almost all liquids with high accuracy, including slurries. However, the pollution of the pipeline may influence the accuracy.
Vortex flowmeter is to place a non-streamlined vortex maker in the fluid, and the vortex speed and fluid speed is with a certain proportion, so as to calculate the volume flow rate. Vortex flowmeter is applicable to measure liquid, gas or steam. It has no moving parts and no fouling problem. Vortex flowmeter will produce noise, and has a higher requirement of the flow rate to produce a vortex.
To measure the flow rate by measuring the rise of fluid temperature or reducing of the thermal sensor. Thermal mass flowmeters have no moving parts or holes, and can accurately measure the flow of gases. Thermal mass flow meter is one of the few technologies capable of measuring the mass flow, and also used to measure large-diameter gas flow.
This flowmeter uses deflection generated by the fluid tube vibration and the corresponding mass flow rate to measure. Coriolis mass flow meter can be used to measure the flow rate of liquids, slurries, gases or vapors. It is with high accuracy. Regular maintenance to the pipe wall is needed to prevent corrosion.
Measuring principle: Faraday's law of electromagnetic induction proves that a conductor moving in a magnetic field inducts an electric potential. By electromagnetic measuring principle, the fluid is a moving conductor. EMF is proportional to the flow rate and detected by two measuring electrodes, and then the transmitter amplifies it, and calculate the flow rate according to the cross sectional area of the pipe. The constant magnetic field is produced by on-off direct current with alternating polarity .
The measuring system includes a transmitter and a sensor.
There are two types of electromagnetic flowmeters: the integration type, the transmitter and the sensor make up a mechanical unit; The separation type, the transmitter and the sensor are installed separately.
The transmitter: Promag50(to operate with button, showing 2 lines) The sensor:PromagW(DN25……2000)