Because all kinds of ultrasonic flowmeters can be installed outside the pipe, non-contact flow measurement, the cost of the instrument is basically independent of the size of the pipe to be tested, while other types of flowmeters increase with the increase in caliber, so the cost is increased. The flowmeter is superior to the other functions of the same type of flowmeter. It is considered to be a good large-diameter flow measuring instrument. The Doppler ultrasonic flowmeter can measure the flow of two-phase medium, so it can be used for the measurement of dirty sewage such as sewers and sewage. In power plants, the use of portable ultrasonic flowmeters to measure large pipe diameters such as turbine water inflow and turbine circulating water is much more convenient than in the past. Ultrasonic flow juice can also be used for gas measurement. Pipe diameters range from 2cm to 5m, from a few meters wide open channels, culverts to 500m wide rivers.
In addition, the accuracy of the flow measurement of the ultrasonic measuring instrument is almost independent of the temperature, pressure, viscosity, density and other parameters of the measured fluid, and can be made into non-contact and portable measuring instruments, so it can solve the problem that other types of instruments are difficult to measure. Flow measurement problems for corrosive, non-conductive, radioactive, and flammable and explosive media. In addition, in view of the non-contact measurement characteristics, coupled with reasonable electronic circuits, one instrument can adapt to a variety of pipe diameter measurements and a variety of flow range measurements. The adaptability of ultrasonic flowmeters is also unmatched by other instruments. Ultrasonic flowmeters have some of the above advantages, so it has received more and more attention and has been developed into a series of products and generalization. It has been made into standard, high-temperature, explosion-proof and wet instruments of different channels to adapt to different media. Flow measurement for occasions and different pipeline conditions.
Vortex flowmeter installation method
1. The vortex flowmeter can only be measured in one direction. The installation should pay attention to ensure that the direction of the medium flow is consistent with the direction indicated by the flowmeter arrow.
2. The best installation method of the vortex flowmeter is vertical installation, and the medium passes through the flowmeter from bottom to top. Install the flowmeter on a vertical pipe with the flow direction from bottom to top.
3. When installing horizontally, the flowmeter must be installed in the high pressure zone of the whole system and ensure the corresponding outlet pressure; do not install at the highest point of the pipeline, because the highest point is often gas accumulation, the pipeline is not full, and the outlet cannot be directly emptied.
4. When measuring high temperature fluid, try to use vertical installation; if you have to install horizontally, please install the transmitter part of the flowmeter vertically downwards or horizontally to avoid excessive temperature; pay attention to air flow at installation location Or well ventilated.
5. Straight pipe section requirements: at least 15 times the pipe diameter before the flow meter and 5 times the pipe diameter after the flow meter. If there are elbows, indents, expansions and other sources of interference in front of the flowmeter, the diameter of the flowmeter should be 30–40 times, and the diameter of the flowmeter should be 6 times. The flow meter should be installed upstream of the regulator valve, pressure or temperature sensor.
6. When installing, pay attention to the pipe diameter should be slightly larger than or equal to the inner diameter of the instrument.
7. When using the sealing ring, the inner diameter of the sealing ring should be slightly larger than or equal to the inner diameter of the instrument, and the center of the sealing ring is at the center of the pipe.
The working principle of the impeller type flowmeter is that the impeller is placed in the fluid to be measured, and is rotated by the impact of the fluid flow, and the flow rate is reflected by the speed of the impeller rotation. Typical impeller flow meters are water meters and turbine flow meters, which may be of mechanical transmission output or electrical pulse output. Generally, the water meter output of the mechanical transmission has low accuracy and the error is about ±2%, but the structure is simple and the cost is low. The domestic production has been mass-produced, standardized, generalized and serialized. The accuracy of the turbine flowmeter for electrical pulse signal output is high, with a typical error of ±0.2% to 0.5%.
Differential pressure flowmeter (variable pressure drop flowmeter)
The differential pressure flowmeter consists of a primary device and a secondary device. The primary device is called a flow measuring element and is installed in the pipe of the fluid to be measured, generating a pressure difference proportional to the flow rate (flow rate) for the secondary device to display the flow rate. The secondary device is called a display instrument. It receives the differential pressure signal generated by the measuring component and converts it to the corresponding flow for display. The primary device of the differential pressure flow meter is often a throttling device or a dynamic pressure measuring device (piteron, constant velocity tube, etc.). The secondary device is equipped with various mechanical, electronic and combined differential pressure gauges with flow display instruments. The differential pressure sensitive components of the differential pressure gauge are mostly elastic components. Since the differential pressure and the flow rate are in a square root relationship, the flow display instrument is equipped with an open square device to linearize the flow scale. Most meters also have a flow accumulator to display cumulative flow for economic accounting. This method of measuring flow using differential pressure has a long history and is relatively mature. Generally, countries all over the world use it in more important occasions, accounting for about 70% of various flow measurement methods. The flow measurement of the main steam, feed water, condensate, etc. of the power plant is based on this meter.