The commonly used types and characteristics of the flow meter
Fluid flow measuring instrument called a flowmeter or flow meter, flowmeter is one of important instrument in industrial measurement, with the development of industrial production, on the fluid flow measurement accuracy and scope of the demand is higher and higher, flowmeter technology changes with each passing day, in order to adapt to a variety of purposes, various types of flowmeter in succession. More than one hundred different now in use of the flowmeter. From a different perspective, flowmeter has the different classification. There are two kinds of commonly used classification, one is according to the principle of measurement of the flow meter adopts classification; Second, according to the meter structure classification principle.
1, according to the measurement principle of classification
(1) the mechanics principle: the principle of the instrument using Bernoulli's theorem of differential pressure type, rotor type; East bright theorem of impulse type, movable type; Using the Newton's second law directly quality type; By using the fluid east bright target type; Using the angular momentum theorem of the turbine; The use of fluid vibration principle of spiral type, vortex street type; Using total static pressure difference of pitot tube type and displacement and weir trough type and so on.
(2) the electrical principle: the principle of the instrument with electromagnetic, differential capacitive, inductive, strain resistance type, etc.
(3) acoustic principle: using the acoustic principle flow such as ultrasonic wave and shock wave type.
(4) thermal principle: using the principle of thermal flow measurement has heat type, direct calorimeter, indirect calorimetry, etc.
(5) optical principle: laser type, photoelectric, etc.
(6) atomic physics principle: nuclear magnetic resonance (NMR) type, radiation type, etc.
2, according to the meter structure principle of classification
According to the actual situation of the current meter products, according to the principle of flow meter structure, divide several:
(1) the volumetric flowmeter
Volumetric flowmeter is equivalent to a standard container volume, constant flow of medium measure. The flow rate, the greater the measurement, the more the higher the frequency of the output. The principle of the volumetric flowmeter is simple. Apply measurement medium with high viscosity, low coefficient. According to the shape of rotors is different, the production of products: used to measure liquid flow in the oval gear flowmeter, waist wheel flow meter (roots flowmeter), rotary piston and scraper flowmeter; Servo type volume flow meter for measuring gas flow meter, skin diaphragm and Jane flowmeter, etc.
(2) the impeller flow meter
Working principle of the impeller type flowmeter is puts the impeller flow in the body, by the impact of the fluid flow and rotation, with the size of the impeller rotating speed to reflect the traffic. Typical impeller type flowmeter is the water meter and turbine flowmeter, the structure can be a mechanical rotating output type or electrical pulse output type. General mechanical transmission of the output water meter accuracy is low, but the structure is simple, low cost, the domestic has batch production, and standardization, generalization and seriation. Electrical pulse signal output of the turbine flowmeter accuracy is higher.
(3) the differential pressure type flowmeter
Differential pressure type flowmeter consists of a device and a second device, a device called the flow measurement device, is installed in the current body of the pipe, production and flow rate (velocity) is proportional to the pressure difference, for the display device to secondary flow. Secondary device called display instrument. Mainly receive the differential pressure signal from the measuring to produce, and the corresponding flow will be converted to display. Differential pressure flow meter a device used for throttling device, the secondary device for all kinds of mechanical, electronic, combined differential gauge display instrument with the flow. Differential gauge of differential pressure sensitive for the elastic, due to the differential pressure or flow is the square root relationship, so the flow display instrument with open square device, so that the flow calibration linearization. We haven't most instrument equipped with flow integrating device, to display the accumulated flow, so that the economic accounting. This by using the method of differential pressure measurement meter long history, more mature, the world is generally used in a more important occasion, the mainstream of flow measurement methods, main generator steam, water supply, water flow measurement using the flow meter.
(4) the area of flowmeter
Under the big small conical flow channel in the float force and move by fluid flows from bottom to top. When the "show the weight of force and float" (float itself will go to it by the weight of the fluid buoyancy) phase equilibrium, the float is stationary. The height of the float (can be used as a measure of the flow volume. Due to the flow cross-sectional area flowmeter vary with different float height, stable and float fixed when the pressure difference between the upper and lower parts are equal, therefore the meter says variable area flowmeter or pressure drop flowmeter, etc. The typical instrument of this flowmeter is rotor flowmeter (float).
(5) the momentum of the flowmeter
By measuring the momentum of the fluid momentum reaction flow according to the size of the flowmeter flowmeter, as a result of the flow of fluid momentum P and fluid density and is proportional to the square of the velocity v, and P = v squared, when determined by flow section, v is proportional to the volume flow rate Q, P = Q squared. Set proportion relations for A, Q = A, therefore, lateral P, reaction flow Q. This form of flowmeter, mostly use the momentum into the detecting stress, displacement and force, and then measure flow. The type of flow meter is wing plate and the target type flowmeter.
(6) pulse flowmeter
Using the impulse theorem of measuring flow meter according to pulse flowmeter, used for measuring the flow meter of granular solid medium, also used for measuring the mud, crystal type liquid and abrasive flow rate. The flow measurement range from a few kilograms to nearly ten thousand tonnes per hour. Typical instrument is the horizontal component of the impulse type flowmeter, its measurement principle is when falling from a certain height to the measured medium has a tilt Angle measurement board to create a momentum, momentum hungry horizontal component force is directly proportional to the mass flow rate, so the measurement of the horizontal component can reflect the size of the mass flow rate. According to the signal detection method, the displacement detection and direct load flow score.
(7) electromagnetic flowmeter
Electromagnetic flowmeter is the application of conductive magnetic field movement in the production of induction electromotive force, and induced electromotive force and the flow rate is proportional to the size, by measuring electromotive force to reflect the principle of pipe flow. Measurement process ensures the liquid state, the tube is filled with its measuring precision and sensitivity is higher. Industry on how to measure the rate of flow of water, pulp and other media. Measurable maximum diameter of 3000 mm, and minimal pressure loss. But the low conductivity medium, such as gas, steam, etc will not be used. Electromagnetic flowmeter cost is higher, and the model is vulnerable to external magnetic field interference, affect the extensive application in industrial tube flow measurement. Therefore, to continuously improve product updates, increase the anti-jamming module, and to the development of computerization.
(8) ultrasonic flowmeter
Ultrasonic flowmeter is based on the speed of ultrasonic wave propagation in a flow medium is equal to the average of the measured medium velocity and acoustic velocity itself geometric principle and design. Also is to reflect the flow by the flow speed. Ultrasonic flowmeter, although did not appear in the 70 s, because can be made into the non-contact type, and opening the flow measurement with the ultrasonic level meter linkage, disturbance and resistance to the fluid does not produce, so it was very popular, is a kind of very promising flowmeter.
Ultrasonic flow meter according to the measurement principle is divided into the time difference and doppler
Jet lag, manufactured by means of the jet lag far flowmeter to wide attention and use of this year, is currently the most used an ultrasonic flowmeter.
Using the doppler effect to make the ultrasonic doppler flowmeter for measuring the dielectric medium have suspended particles or bubbles, use has certain limitations, but it has solved the time difference ultrasonic flowmeter intelligent measurement problem of the single clear fluid, is also thought to is a contact measurement two-way flow of the ideal instrument.
(9) fluid oscillation flowmeter
Fluid oscillation flowmeter is the use of fluid flow under the condition of a specific port will produce oscillation, and the frequency of the oscillation and the flow rate is proportional to the design of the hospital, when the flow cross section must flow rate is proportional to the volume flow guide. Therefore, measure the oscillation frequency can be measured flow, the flowmeter is developed and developed in the 70 s. Due to both the advantages of no moving parts and pulse digital output, is very promising. The typical products are vortex flowmeter and vortex precession flowmeter.
(10) mass flowmeter
Due to the volume of fluid temperature. The effects of parameters such as pressure, volume flow said flow should be given the parameters of the medium size. Under the condition of the medium parameters changing, often difficult to meet the requirements, and cause the instrument shows value distortion. Therefore, the mass flowmeter is widely used and valued. Direct and indirect mass flow scoring two kinds. Type mass flowmeter directly by using the principle of mass flow rate directly related measure, at present commonly used quantity heat type, type, vibratory gyro angular momentum, the coriolis force to magnus effect type and type and other mass flowmeter. Indirect mass flowmeter is obtained directly multiplied by densimeter in volume flow to mass flow.
In the modern industrial production, the operation parameters, such as temperature, pressure of flow medium, in the case of high temperature and high pressure, due to reasons such as material and structure, mass flowmeter applied directly meet with difficulties, but indirect mass flowmeter by densitometer restricted by humidity and pressure scope, often also is bad to practical application. Widely used in industrial production, therefore, temperature compensating mass flowmeter. Can be seen as a kind of indirect mass flowmeter, not with density meter, but the use of the relationship between temperature, pressure and density, with temperature and pressure signals by the functional operation of density, and volume flow multiplication and mass flow rate. Current temperature compensating pressure mass flowmeter is practical, but when the parameters of the measured medium range is very big or very quickly, correctly and compensation is very difficult or impossible, so further research in the mobile phone production applicable mass flowmeter and density meter or a subject.
Above all commonly used structure principle of the flowmeter than many various structure of flowmeter, if applicable Precession vortex flowmeter of various weir flowmeter, groove type flowmeter; For large diameter measurement insert flowmeter; Laminar flow meter measuring laminar flow; Applicable correlation method of two phase flow measurement of flow meter; And laser method, nuclear magnetic resonance (NMR) method, flow meter and a variety of tracer method, dilution method, etc. With the development of science and technology and the need of practical application, a new flow meter will continue to the emergence of flowmeter types will be more complete.