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Various flow meter principle introduction
A differential pressure flowmeter
1, orifice flowmeter (standard orifice, nozzle)
1) Principle
Filled with fluids, when they flow through the orifices in the tubes, the flow bundles will form a local contraction at the orifices, so that the flow rate increases, the static pressure is low, so there is a pressure drop before and after the orifices, that is, the pressure difference, The greater the flow of medium flow, the greater the pressure difference between the front and back of the orifice, so you can measure the pressure difference to measure the size of the fluid flow. This measurement method is based on the law of energy conservation and the law of continuity of flow.
2) Structure
(1) Throttling elements: standard orifice plate, standard nozzle, long diameter nozzle, 1/4 round orifice plate, double orifice plate, eccentric orifice plate, round orifice plate, conical inlet orifice plate
(2) Pressure taking device: ring chamber, pressure flange, clamping ring, pressure guiding tube, etc.
(3) Connection flange
(4) Measuring tube
2, Venturi flow meter
1) Principle
The inner venturi tube consists of a circular measuring tube and a special type core body which is placed in the measuring tube and coaxial with the measuring tube. The radially outer surface of the special core body has a similar geometric shape to the inner surface of the classic venturi tube, and forms a different-diameter annular over-current gap between the inner surface of the measuring tube and the inner surface of the measuring tube. The throttling process of the fluid flowing through the inner venturi is basically similar to the throttling process of the fluid flowing through the classic venturi tube and the annular orifice plate. The structural characteristics of the inner venturi tube do not have the problem of sharp edge abrasion and accumulation of the orifice plate throttling element during use, and the gradient of the velocity distribution of the fluid in the tube before throttling and various possible existences thereof. The non-axisymmetric velocity profile allows efficient flow adjustment (rectification) to achieve highly accurate and highly stable flow measurements.
3, average speed tube flow meter, Pitobba flow meter (Pitot principle type)
1) Principle
A small hole called the total pressure hole is formed in the direction of the head of the pitot tube, and a "stationary point" is formed at this point. A number of static pressure holes perpendicular to the flow direction of the fluid are opened at a certain distance from the head. The static pressure measured at each static pressure hole is output after the pressure in the pressure equalizing chamber is equalized. Since the difference between the total pressure and the static pressure of the fluid has a definite numerical relationship with the flow velocity of the fluid to be measured, the fluid flow rate can be measured with a pitot tube. The size of the measured flow.
2) Structure
The pitot tube flowmeter is a double-decker, hollow-rectangular bone that is bent at right angles and has multiple pressure-receiving holes for simultaneous measurement of total fluid pressure and static pressure. It is used with differential pressure transmission and flow indicator.
Second, electromagnetic flowmeter
1) Principle
An electromagnetic flowmeter that measures the flow velocity of a medium using the principle of electromagnetic induction. It adds a magnetic field on both sides of the pipe. The measured medium flows through the pipe and cuts the magnetic line of force. The induced electric potential is generated at the two detection electrodes. The size is proportional to the motion of the fluid. speed. Electromagnetic flowmeter is characterized by no moving parts and parts protruding from the fluid, with high reliability, can be used to measure acid, alkali, salt solution, coal slurry, pulp, mortar, mortar, pulp, resin, The flow of various suspensions, gasified vapors and viscous substances such as rubber latex, synthetic fiber pulp and emulsions.
2) Structure
The electromagnetic flowmeter is simply composed of a flow sensor and a transmitter.
The flow sensor converts the volumetric flow of conductive liquid flowing through the conduit into a linear electrical signal. Its conversion principle is the famous Faraday's law of electromagnetic induction, that is, the conductor passes through a magnetic field, cuts the electromagnetic wire, and generates an electromotive force. The magnetic field of the flow sensor is realized by excitation, which is divided into DC excitation, AC excitation and low frequency square wave excitation. Most current flow sensors use low-frequency square-wave excitation.
The transmitter is composed of excitation circuit, signal filtering and amplification circuit, A/D sampling circuit, microprocessor circuit, D/A circuit and transmission circuit.
Third, vortex flowmeter
1) Principle
The vortex flowmeter uses the fluid oscillation principle to measure the flow. When the fluid passes through the vortex flow transmitter in the pipeline, two columns of vortices proportional to the flow velocity are alternately generated above and below the vortex generating body of the triangular column. The frequency of release of the vortex is The average velocity of the fluid flowing through the vortex generator is related to the width of the vortex generator.
2) Structure
Vortex flowmeter is composed of vortex generators, detection probes and corresponding electronic circuits designed in the flow field.