There are many kinds of flowmeters according to the working principle, and the selection needs to choose the right flowmeter according to the actual working conditions. Let's talk about 6 kinds of flowmeters commonly used in sewage treatment.

一、Electromagnetic Flowmeter

Electromagnetic flowmeter is a flow measuring instrument based on the principle of electromagnetic induction. It consists of a sensor and a transmitter.

1. Famous Brand

Well-known brands include Kekun Fuji E+H, Cologne, Yokogawa, Rosemount, Siemens, Emerson, ABB and so on.

2. Operating Principle

The basic principle of the electromagnetic flowmeter is: outside the pipe made of general non-magnetic materials, a pair of magnetic poles N and S are installed to generate a magnetic field. When the conductive liquid flows through the pipeline, the magnetic induction electromotive force generated by the fluid cutting the magnetic force line, the induced potential is led by the two electrodes in the vertical direction of the magnetic pole, when the strength of the magnetic field is unchanged, the diameter of the pipeline is certain, the size of the induced potential is only related to the flow rate, the size of the induced potential is passed to the display instrument, the flow rate can be read.

3. Advantage

1) There are no moving parts and fluid resistance in the measuring catheter, so the pressure loss is small, no mechanical inertia, so the response is sensitive;

2) Wide measuring range: range ratio is generally 10:1, up to 100:1, flow rate range is generally 1-6m/s, can be extended to 0.5-10m/s; Flow range from 90mL/h to more than 100,000 m3/h; Pipe diameters range from 2mm to 2400mm or 3000mm;

3) Can measure the volume flow of liquid containing solid particles, suspended matter or acid, alkali, salt solution with a certain conductivity, can also measure the pulsation flow, and can be measured bidirectional;

4) There is a wired relationship between the flow signal and the volume flow of the fluid, so the instrument has a uniform scale; And the volume flow of the fluid has nothing to do with the physical properties of the medium and the flow state, so the electromagnetic flowmeter can be used to measure the volume flow of other conductive liquids without correction after only water calibration;

5) Compared with most other flow meters, the front straight pipe section has lower requirements.

4. Disadvantage

1) The use of temperature and pressure can not be too high;

2) Limited application range, can not be used to measure the flow of non-conductive fluids such as gas, steam and petroleum products and fluids containing more and larger bubbles;

3) When the flow rate and velocity distribution do not meet the set conditions, there will be a large measurement error;

4) When the flow rate is too low, it is difficult to amplify and measure the induced potential of the order of magnitude with the interference signal, and the instrument is also prone to zero drift;

5) The signal of the electromagnetic flowmeter is relatively weak, and a slight interference from the outside can affect the accuracy of the measurement.

二、Ultrasonic Flowmeter

Ultrasonic flowmeters are instruments that measure volume flow by detecting the effect of ultrasonic beam (or ultrasonic pulse) on fluid flow.

1. Famous Brand

Famous brands are FUJI Rosemount, E+H, Cologne, Flaxen, GE, Panasonic and so on.

2. Operating Principle

The sound wave propagates in the fluid, the sound wave propagates in the direction of the current will increase, the countercurrent direction will decrease, and the same propagation distance will have different propagation time. The propagation time method is to use the relationship between the propagation velocity difference and the velocity of the measured liquid to obtain the velocity and the flow rate combined with the diameter of the pipe.

3. Advantage

1) Ultrasonic flowmeter can be used for non-contact measurement, clamping transducer Ultrasonic flowmeter can be installed without stopping the flow carrier pipe, as long as the transducer is installed outside the pipeline to be tested, that is, the flow can be measured with ultrasonic flowmeter on the existing pipeline that can not be broken or can not be drilled;

2) Ultrasonic flowmeter is no flow resistance radial measurement, no additional pressure loss;

3) The instrument coefficient of the measuring meter can be calculated from the actual measurement pipe and sound channel and other geometric dimensions, which can be calibrated by dry method, except for the measurement pipe segment, it is generally not necessary to do real flow verification;

4) Ultrasonic flowmeter is suitable for large circular and rectangular pipelines, and is not limited by pipe diameter in principle, and its cost is basically independent of pipe diameter;

5) Doppler ultrasonic flowmeter can measure liquid with more solid phase content or containing bubbles.

4. Disadvantage

1) The ultrasonic flowmeter in the propagation time method can only be used to clean liquids and gases, and can not measure suspended particles and bubbles that exceed a certain range of liquids; On the contrary, Doppler LSF can only be used to measure liquids containing certain out-of-phase.

2) Doppler ultrasonic flowmeter in most cases, the measurement number is not high;

3) Can not be used for pipe diameter less than DN13mm.

三、Insert Type Turbine Flowmeter

The plug-in eddy-flow meter is mainly composed of an expansion ring, an impeller, a rear guide, a turbine head shell, a limit plate cutting handle, a transmitter mounting bolt, an insertion rod, a locking bolt, and a positioning rod signal transmission line.

1. Fmaous Brand

Plug-in turbine flowmeter famous brands are Famet, E+H, Yokogawa and so on.

2. Operating Principle

A freely rotating impeller is installed in the fluid flow pipeline. When the fluid flows through the measured pipeline, the impeller in the turbine head is driven to rotate. Within a wide measuring range, the rotating speed of the impeller is proportional to the flow rate in the measured pipeline. The speed of the impeller and the electrical pulse signal of the speed are detected by the reluctance and magnetic block detector, and then transmitted to the display instrument after amplification by the preamplifier. Instantaneous flow and total volume can be measured.

3. Advantage

1) The measurement of the direct contact water of the turbine head is more accurate, and the signal can be transmitted to the central control room after being amplified by the pre-amplifier plate;

2) The flow meter has a small volume, can measure large flow, and can also measure cumulative flow more accurately while measuring flow;

3) Low cost, a set of turbine head is only about 400 yuan

4. Disadvantage

Due to maintenance problems, the count cannot be continuous, the output signal is 0 to 10mA, and there is no serial communication interface.

四、Rotameter

Rotameter is to change the flow area of the fluid to keep the differential pressure above and below the rotor constant, so it is also called the variable flow area constant differential pressure flowmeter, also known as the float flowmeter.

1. Famous Brand

Famous brands are meister, Yokogawa, Dwyer, Cologne, Yokogawa, Kroni and so on.

2. Operating Principle

The rotameter measures the flow of fluid according to the throttling principle. In a vertical conical tube that expands from the bottom up, the gravity of the circular cross section float is borne by the hydrodynamic force, and the float can rise and fall freely within the conical tube. It moves up and down under the action of velocity and buoyancy, and after balancing with the weight of the float, it is transmitted to the dial through magnetic coupling to indicate the flow rate.

3. Advantage

Suitable for small pipe diameter and low flow rate; Reliable work, small maintenance, long life; The requirements for the downstream straight pipe section are not high; Has a wide flow range of 10:1; Local pointer indication is close to linear; Intelligent indicator with LCD liquid crystal display, can display instantaneous, cumulative flow, can also output pulse, output alarm; With temperature compensation.

4.Disadvantage

1) There is a risk of glass tube breakage;

 

2) Most structural float flowmeters can only be used for pipeline installation of vertical flow from the bottom up;

 

3) The application is limited to small and medium-sized pipe diameters, and ordinary full-flow float flowmeters cannot be used for large pipe diameters;

 

4) When the fluid is used and the factory calibration fluid is different, the flow indication value should be corrected, such as the actual use of fluid density and viscosity are different, the flow should deviate from the original index value, and the conversion correction should be made.

五、Throttling flowmeter

Throttle flowmeter is a typical differential pressure flowmeter, which is the most commonly used flow meter for measuring gas, liquid and vapor flow in early industrial production.

1. Famous Brand

The main brands of throttling flow meters are KEBitobar, ABB, Emerson, Krohne, Siemens and so on.

2. Operating Principle

A hole plate saving part is added in the fluid pipeline, and the differential pressure transmitter is introduced through the pressure guide tube to measure the differential pressure on the upper and lower reaches of the saving part.

 

3.Advantage

1) Throttle parts standard orificule structure is easy to copy, simple, firm, stable and reliable performance, long service life, low price;

 

2) Throttle type application range is extremely wide, all single-phase fluids, including liquid, gas, steam can be measured, some miscible flows, such as gas-solid, gas-liquid, liquid-solid, etc., can also be applied, general production process and pipe diameter, working state (pressure, temperature) have products;

 

3) accessories manufacturers can be universal, if the international standard and can not be calibrated;

 

4) Easy installation and maintenance, unlike ordinary differential flowmeters, long pressure pipeline, easy to leak, easy to block, easy to freeze;

 

5) There is no zero drift problem.

 

4. Disadvantage

1) The repeatability and accuracy of the measurement are at a medium level;

 

2) The range is narrow, due to the square relationship between the instrument signal and the flow, the general range can only reach 3:1 ~ 5:1;

 

3) The requirements for on-site installation are high, and it is difficult to meet them if a long straight pipe section is required;

 

4) Pressure pipeline is a weak link, easy to produce leakage, blockage, freezing and signal distortion and other failures;

 

5) Large pressure loss.

 

六、Target Flowmeter

Target flowmeters began to be used in industrial flow measurement in the 1960s, mainly to solve the flow measurement of high viscosity and low Reynolds number fluids.

 

1. Famous Brand

The main brands of target flowmeter are Omega, Hilton, Said, tecfluid and so on.

 

2. Operating Principle

When the medium flows in the measuring tube, the pressure difference between its own kinetic energy and the target plate is generated, and the force on the target plate is generated, so that the target plate produces a small amount of displacement. The force is proportional to the square of the velocity of the medium, and the force of the target plate is transmitted through the target rod, causing a small change in the elastomer of the sensor, thus breaking the bridge balance composed of the patch capacitor and generating a voltage signal corresponding to the force of the flow on the target plate.

 

3. Advantage

1) Wide measuring scale, low flow rate, especially suitable for large pipe diameter, high and low pressure gas or liquid measurement;

 

2) With integrated temperature, pressure compensation, direct output quality or standard flow;

 

3) With optional small signal excision, nonlinear correction, filtering time can be selected;

 

4) Easy to install, good repeatability, fast measurement, easy to maintain;

 

5) Dirt resistance, high temperature resistance, high sensitivity, anti-blocking and anti-interference, anti-impurities and other capabilities;

 

6) Low pressure loss.

 

4. Disadvantage

1) Not suitable for fluid switch very frequent conditions, continuous work in the case of better application;

 

2) The accuracy is not very high, generally used as a process control metering instrument, trade settlement with caution;

 

3) The range is narrow, the general instrument is 10:1 range;

 

4) Because the target plate and target rod of the target flowmeter have their own weight, the zero point must be reset after installation.