Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flowmeter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters have been put into use. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods. One is to classify according to the measurement principle adopted by the flowmeter: the second is to classify according to the structural principle of the flowmeter.
Sort by measurement principle
a. Mechanical principle:
Instruments belonging to such principles have differential pressure type, rotor type using Bernoulli's theorem;
Impulse type using the momentum theorem, movable tube type;
Direct mass equation using Newton's second law;
a target using the principle of fluid momentum;
Turbine using the angular momentum theorem;
Vortex type using vortex principle of fluid oscillation;
Use the total static pressure difference of the pitot tube type as well as volumetric and sputum, trough and so on.
b. Electrical principle:
Differential capacitor type,
Strain resistance type, etc.
c. Acoustic principle:
d. Thermal principles:
Indirect calorimetry and so on.
1. Measurements are not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
2. There is no obstructed flow component in the measuring tube, no pressure loss, and the requirements of the straight pipe section are low. Unique adaptability to slurry measurement;
3. Reasonable selection of sensor lining and electrode materials, that is, good corrosion resistance and wear resistance;
4. The converter adopts novel excitation mode with low power consumption, stable zero point and high precision. The flow range can reach 150:1;
5. The converter can be integrated with the sensor or separated;
6. The converter adopts 16-bit high-performance microprocessor, 2x16LCD display, convenient parameter setting and reliable programming;
7. The flowmeter is a two-way measuring system with three totalizers: positive total, reverse total and total difference; can display positive and negative flow, and has multiple outputs: current, pulse, digital communication , HART;
8, the converter uses surface mount technology (SMT), with self-test and self-diagnosis function;
9. Measurement accuracy is not affected by changes in fluid density, viscosity, temperature, pressure and conductivity. The sensor induced voltage signal has a linear relationship with the average flow velocity, so the measurement accuracy is high.
10. There is no obstruction in the measuring pipe, so there is no additional pressure loss; there is no moving parts in the measuring pipe, so the life of the sensor is extremely long.
11. Since the induced voltage signal is formed in the entire space filled with the magnetic field and is the average value on the pipeline surface, the sensor requires a short straight pipe section and a pipe diameter of 5 times.
12. The converter adopts the latest and most advanced single-chip microcomputer (MCU) and surface mount technology (SMT) in the world. It has reliable performance, high precision, low power consumption, stable zero point and convenient parameter setting. Click on the Chinese display LCD to display the cumulative flow, instantaneous flow rate, flow rate, flow percentage, and more.
13, two-way measurement system, can measure forward flow, reverse flow. Special production technology and high-quality materials ensure that the performance of the product remains stable for a long time.
Measuring principle of electromagnetic flowmeter
The principle of electromagnetic flowmeter measurement is based on Faraday's law of electromagnetic induction. The measuring tube of the flow meter is a non-magnetic alloy short tube lined with an insulating material. The two electrodes are fixed to the measuring tube through the tube wall in the tube diameter direction. The electrode tip is substantially flush with the inner surface of the liner. When the exciting coil is excited by the bidirectional square wave pulse, a working magnetic field having a magnetic flux density B is generated in a direction perpendicular to the axis of the measuring tube. At this time, if the fluid having a certain conductivity passes through the measuring tube, the cutting magnetic line induces the electromotive force E. The electromotive force E is proportional to the product of the magnetic flux density B, the inner diameter D of the measuring tube and the average velocity V. The electromotive force E (flow signal) is detected by the electrode and sent to the converter through the cable. After the converter amplifies the flow signal, it can display the fluid flow, and can output signals such as pulse and analog current for flow control and regulation.