Here are my following understandings:
In order to obtain the best concentration of the mixture in all operating conditions, it is necessary to correctly measure the amount of air sucked into the engine at each instant, as the ECU calculates (controls) the amount of fuel injected The main basis. If the air flow sensor or line failure, ECU can not get the correct air intake signal, it can not be normal fuel injection control, will cause the mixture is too thick or too thin, so that the engine is not working properly.
The basic principles and types of ultrasonic flowmeter Ultrasonic waves in the flow of fluid when the flow of information on the flow. The flow rate of the fluid can be detected by the received ultrasonic wave, and the flow rate is converted into the flow rate. According to the detection method, can be divided into propagation velocity difference method, Doppler method, beam shift method, noise method and correlation method and other different types of ultrasonic flowmeter. Sonic flow meter is nearly a decade with the rapid development of integrated circuit technology began to use .
Non-contact instrument, suitable for measuring the fluid is not easy to contact and observation and large diameter flow. It is linked to the water level meter to measure the flow of open water. The use of ultrasonic flow than the installation of measuring elements in the fluid does not change the flow of fluid state, does not produce additional resistance, instrument installation and maintenance can not affect the production pipeline operation is thus an ideal energy-saving flow meter.
As we all know, the current industrial flow measurement ubiquitous large diameter, large flow measurement difficult problem, because the general flow meter with the increase in measuring diameter will bring manufacturing and transport difficulties, cost increase, Large, installation not only these shortcomings, ultrasonic flowmeter can be avoided. Because all kinds of ultrasonic flowmeter can be installed outside the tube, non-contact flow measurement, the instrument cost is basically independent of the size of the pipe under test, and other types of flowmeter with the increase in caliber, the cost of a substantial increase, so the greater the diameter of ultrasound Flow meter than the same function other types of flow meter function price ratio is superior. Is considered to be a good large diameter flow measurement instrument, Doppler ultrasonic flowmeter can measure the flow of dual-phase medium, it can be used for sewage and sewage and other dirty sewage measurement. In the power plant, the use of portable ultrasonic flowmeter to measure the turbine water intake, turbine circulation water and other large diameter flow than the past skin detachment flow meter is much more convenient. Ultrasonic flow meters can also be used for gas measurement. The application of the diameter from 2cm to 5m, from a few meters wide open channel, underground canal to 500m wide river can be applied.
In addition, the ultrasonic measurement instrument flow measurement accuracy is almost not measured fluid temperature, pressure, viscosity, density and other parameters, but also made of non-contact and portable measuring instruments, it can solve the other types of instruments difficult to measure the strong Corrosive, non-conductive, radioactive and flammable and explosive media flow measurement problems. In addition, in view of non-contact measurement characteristics, coupled with a reasonable electronic circuit, a meter can adapt to a variety of diameter measurement and a variety of flow range measurement. Ultrasonic flowmeter adaptability is also unmatched by other instruments. Ultrasonic flowmeter has some of the advantages of the above, so it is more and more attention and to the product serialization, general development, has been made of different channels of standard, high temperature, explosion-proof, wet type instrument to adapt to different media, different Time and flow conditions for different piping conditions.
Ultrasonic flowmeter present shortcomings are mainly measurable fluid temperature range by the ultrasonic transducer aluminum and the transducer and the coupling between the pipe temperature limit, as well as the measured temperature at high temperature acoustic data of the original data Incomplete At present, China can only be used to measure the fluid below 200 ℃. In addition, the ultrasonic flowmeter measurement lines than the general flow meter complex. This is because the general industrial measurement of liquid flow rate is often a few meters per second, while the sound waves in the liquid in the propagation speed of about 1500m / s or so, measured fluid flow rate (flow) changes to the maximum speed of sound changes is 10- 3 orders of magnitude. If the accuracy of the measured flow rate is 1%, the accuracy of the measurement of the speed of sound to 10-5 ~ 10-6 order of magnitude, it must be a perfect measurement line can be achieved, which is exactly the ultrasonic flowmeter only in the integrated circuit Technology under the premise of rapid development in order to get the practical application of the reasons.
Ultrasonic flowmeter consists of ultrasonic transducer, electronic circuit and flow display and accumulation system composed of three parts. Ultrasonic emission transducer converts electrical energy into ultrasonic energy and transmits it to the measured fluid. The ultrasonic signal received by the receiver is amplified by an electronic circuit and converted to an electrical signal supply display and an integrated meter for display. And total. This enables the detection and display of traffic.
Ultrasonic flowmeter commonly used piezoelectric transducer. It utilizes the piezoelectric effect of the piezoelectric material, and uses the appropriate emission circuit to add the electric energy to the piezoelectric element of the transmitting transducer to produce ultrasonic vibration. The ultrasonic waves are propagated at an angle into the fluid and then received by the receiving transducer and turned into electrical energy by the piezoelectric element for detection. The transmitting transducer utilizes the inverse piezoelectric effect of the piezoelectric element, while the receiving transducer utilizes the piezoelectric effect.
Ultrasonic flowmeter transducer piezoelectric components are often made into round flakes, vibrating along the thickness. The diameter of the sheet exceeds 10 times the thickness to ensure the directionality of the vibration. Piezoelectric element materials are mostly lead zirconate titanate. To fix the piezoelectric element, so that the ultrasonic wave into the fluid at the appropriate angle, the need for the components of the human voice wedge, constitute the whole transducer (also known as the probe). Acoustic wedge material not only requires high strength, anti-aging, and requires ultrasonic vibration after the wedge energy loss is small, that is close to 1 transmission coefficient. Commonly used wedge material is plexiglass, because it is transparent, you can observe the sound wedge in the assembly of piezoelectric components. In addition, some rubber, plastic and bakelite can also be used for wedge material.
Ultrasonic flowmeter electronic circuits include transmit, receive, signal processing and display circuits. The measured instantaneous flow and cumulative flow values are displayed in digital or analog quantities.
According to the principle of signal detection, the current ultrasonic flowmeter can be divided into the propagation velocity difference method (including: direct time difference method, time difference method, phase difference method, frequency difference method) beam shift method, Doppler method, correlation method, space Filtering and noise methods and other types, as shown. Which the principle of noise and the structure of the most simple, easy to measure and carry, cheap but low accuracy, suitable for traffic measurement accuracy is not demanding applications. Because the direct time difference method, time difference method, frequency difference method and phase difference method are the basic principle of measuring the ultrasonic pulse downstream and countercurrent transmission speed difference to reflect the flow rate of the fluid, it is collectively referred to as the propagation velocity difference method. Which frequency method and time difference method to overcome the sound velocity with the fluid temperature changes brought about by the error, high accuracy, it is widely used. According to the different configuration of the transducer, the propagation speed difference is divided into: Z method (through method), V method (reflection method), X method (cross method) and so on. Beam shift method is the use of ultrasonic beam in the fluid in the direction of the flow with the fluid flow changes caused by offset to reflect the fluid flow rate, low flow rate, the sensitivity is very low applicability is not. Doppler method is the use of acoustic Doppler principle, by measuring the scattering of scattering in the non-uniform fluid ultrasonic Dop
Le frequency shift to determine the fluid flow, suitable for suspended particles, bubbles and other fluid flow measurement. The correlation method is to measure the flow with the related technology. In principle, the measurement accuracy of this method is independent of the velocity of sound in the fluid, and therefore has nothing to do with the temperature and concentration of the fluid, so the measurement accuracy is high and the application range is wide. But the correlator price is expensive, the line is more complicated. After the popularity of microprocessors applications, this shortcoming can be overcome. The noise method (listening method) is the principle that the noise generated by the fluid flow in the pipe is related to the flow rate of the fluid and the flow rate or flow rate value by detecting noise. The method is simple, the equipment is cheap, but the accuracy is low.
Several of the above methods have their own characteristics, should be based on the measured fluid properties. Flow rate distribution, pipe installation location and the measurement accuracy requirements and other factors to choose. Generally speaking, because the temperature of industrial production in the refrigerant often can not be kept constant, so the frequency difference method and the time difference method. The direct time difference method is used only when the diameter is large. The principle of selection of the transducer installation method is generally that when the fluid flows parallel to the tube axis, the Z method is used; when the flow direction is not parallel to the pipe or the pipe installation site limits the transducer installation interval, Method or X method. When the flow field is not uniform and the front pipe section is short, a multi-channel (eg two-channel or four-channel) can also be used to overcome the flow measurement error caused by the flow rate disturbance. Doppler method is suitable for measuring two-phase flow, can avoid the conventional instrument by the suspended particles or bubbles caused by clogging, wear, adhesion and can not run the ills, and thus to the rapid development. With the development of industrial and energy-saving work, the development of kerosene mixture (COM), coal cement (CWM) fuel transportation and application, and the development of energy-saving methods such as fuel oil and water combustion are all open for Doppler ultrasonic flowmeter applications. prospect.
Those are just my personal understandings. Hope that you can help me get out of trouble. What is your idea ? Do you agree with my ideas ? Any of your ideas would be highly appreciated.
May someone would like to help ?
thanks in advance.