There are many types of flow meters based on their working principles, and the selection of a suitable flow meter needs to be based on the actual operating conditions. Today, I have summarized the working principles of various flow meters for everyone, hoping to be helpful.
01 Differential pressure flow meter
Differential pressure flowmeter is an instrument that calculates flow based on the differential pressure generated by the flow detection component installed in the pipeline, known fluid conditions, and the geometric dimensions of the detection component and pipeline. The differential pressure flowmeter consists of a primary device (detection component) and a secondary device (differential pressure conversion and flow display instrument). Differential pressure flow meters are usually classified in the form of test pieces, such as orifice flow meters, Venturi flow meters, averaging tube flow meters, etc. The secondary devices include various mechanical, electronic, and electromechanical integrated differential pressure gauges, differential pressure transmitters, and flow display instruments. It has developed into a large class of instruments with a high degree of standardization (serialization, generalization, and standardization) and a wide variety of specifications. It can measure both flow parameters and other parameters (such as pressure, level, density, etc.).
The detection components of differential pressure flow meters can be divided into several categories according to their working principles: throttling device, hydraulic resistance type, centrifugal type, dynamic pressure head type, dynamic pressure head gain type, and jet type.
Differential pressure flow meters are the most widely used type of flow meters, with their usage ranking first among various flow instruments. In recent years, due to the emergence of various new types of flow meters, their usage percentage has gradually decreased, but they are still the most important type of flow meter at present.
02 Target Flowmeter
Target flowmeter has been applied to industrial flow measurement since the 1960s, which is mainly used to measure the flow of fluids with high viscosity and low Reynolds number. It has gone through two major stages of development: pneumatic meter and electric meter. SBL series intelligent target flowmeter adopts the latest force sensing sensor as the measurement and sensitive transmission element based on the measurement principle of the original strain gauge (capacitive) target flowmeter, A new type of flow measurement instrument developed by utilizing modern digital intelligent processing technology.
03 Positive displacement flow meter
Positive displacement flow meters, also known as constant displacement flow meters or PD flow meters, are the most accurate type of flow instruments. It uses mechanical measuring elements to continuously divide the fluid into a single known volume part, and measures the total volume of the fluid based on the number of times the measuring chamber repeatedly fills and discharges that volume part of the fluid.
According to the classification of measuring components, volumetric flow meters can be divided into elliptical gear flow meters, scraper flow meters, double rotor flow meters, rotary piston flow meters, reciprocating piston flow meters, disc flow meters, liquid sealed rotary cylinder flow meters, wet gas meters, and membrane gas meters.
04 Turbine Flowmeter
Turbine flowmeter is the main type of velocity flowmeter, which uses a multi blade rotor (turbine) to sense the average flow velocity of the fluid and derive the flow rate or total amount from the instrument. Generally, it consists of two parts: a sensor and a display instrument, and can also be made into a whole.
Turbine flow meters, volumetric flow meters, and mass flow meters are among the three types of flow meters with high repeatability and accuracy, and are one of the top ten types of flow meters.
05 Electromagnetic Flowmeter
Electromagnetic flowmeter is an instrument used to measure conductive liquids based on Faraday’s law of electromagnetic induction.
Electromagnetic flow meters have a series of excellent characteristics that can solve problems that other flow meters are not easy to apply, such as measuring dirty and corrosive flow.
06 Vortex Flowmeter
Vortex street flowmeter is an instrument that places a non streamline vortex generator in the fluid, and the fluid alternately separates and releases two strings of regularly staggered vortex on both sides of the generator. Vortex flow meters can be divided into stress type, strain type, capacitive type, thermal sensitive type, vibrating type, photoelectric type, and ultrasonic type based on frequency detection methods.
07 Ultrasonic flow meter
Ultrasonic flow meters are instruments that measure flow by detecting the effect of fluid flow on ultrasonic beams (or pulses). According to the principle of signal detection, ultrasonic flow meters can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method, and frequency difference method), beam offset method, Doppler method, cross correlation method, spatial filtering method, and noise method.
Ultrasonic flow meters, like electromagnetic flow meters, belong to the category of unobstructed flow meters due to the absence of any obstruction in the flow channel of the instrument. They are suitable for solving the difficult problem of flow measurement, and have prominent advantages in large diameter flow measurement.
08 Coriolis mass flow meter
The Coriolis mass flow meter is a novel instrument that directly and precisely measures fluid mass flow rate. The main structure adopts two U-shaped pipes arranged side by side, causing the bending parts of the two pipes to vibrate slightly towards each other. The straight pipes on both sides will follow the vibration, that is, they will come together or open at the same time, that is, the vibration of the two pipes is synchronous and symmetrical. If the fluid is introduced into the tube while the tube is synchronously vibrating, causing it to flow forward along the tube, the tube will force the fluid to vibrate up and down together.
Thermal mass flow meter
The thermal flow meter sensor consists of two sensing elements, a speed sensor and a temperature sensor. They automatically compensate and correct for changes in gas temperature. The electric heating part of the instrument heats the speed sensor to a certain fixed value higher than the operating temperature, forming a constant temperature difference between the speed sensor and the sensor measuring the operating temperature. When the temperature difference remains constant, the energy consumed by electric heating, or heat dissipation value, is directly proportional to the mass flow rate of the gas flowing through it.
10 metal rotor flowmeter
The rotameter consists of two components, one of which is a conical tube that gradually expands from bottom to top; The other part of the rotameter is a rotor placed in a conical tube and can move freely along the centerline of the tube. When measuring the flow rate of a fluid, the measured fluid flows in from the lower end of the conical tube, and the flow of the fluid impacts the rotor and generates a force on it (the magnitude of this force varies with the flow rate); When the flow rate is large enough, the generated force lifts the rotor and causes it to rise. At the same time, the measured fluid flows through the annular section between the rotor and the conical tube wall, and there are three forces acting on the rotor: the dynamic pressure of the fluid on the rotor, the buoyancy of the rotor in the fluid, and the gravity of the rotor itself.
When the flowmeter is installed vertically, the center of gravity of the rotor coincides with the axis of the conical tube, and all three forces acting on the rotor are parallel to the axis of the tube. When these three forces reach equilibrium, the rotor floats smoothly at a certain position within the conical tube. For a given rotameter, the size and shape of the rotor have been determined, so its buoyancy and self gravity in the fluid are known to be constant. Only the dynamic pressure of the fluid on the float changes with the size of the incoming flow velocity. Therefore, when the incoming flow velocity increases or decreases, the rotor will move up or down, and the flow cross-sectional area at the corresponding position will also change until the velocity reaches equilibrium, and the rotor will stabilize in the new position. For a given rotameter, the position of the rotor in the conical tube corresponds one-to-one with the flow rate of the fluid flowing through the conical tube.
11 Orifice Plate Flowmeter
The fluid filled with the pipeline flows through the throttling device inside the pipeline, causing local contraction near the throttling component, increasing the flow rate, and generating a static pressure difference on both upstream and downstream sides. Given the relevant parameters, the relationship between differential pressure and flow rate can be derived based on the principle of flow continuity and the Bernoulli equation to obtain the flow rate.
12 Open channel flow meter
Different from the above, it is a flow meter for measuring natural flow on free surface in an open channel with non full tubes.
The working principle of an open channel flowmeter is to use open channel technology to measure the liquid level height of the fluid, and then calculate the flow rate through the internal microprocessor of the instrument. Due to its non-contact measurement, open channel flow meters can be applied in harsh environments. The open channel flowmeter is controlled by a microcomputer to transmit and receive the open channel. Based on the transmission time, the distance between the open channel flowmeter and the measured liquid level is calculated to obtain the liquid level height. Due to the proportional relationship between the liquid level and flow rate, the liquid flow rate Q can be ultimately obtained according to the calculation formula.
Post time: 07-06-23