The working principle of the ultrasonic K rm n vortex air flow meter

Metrological principle. A column-shaped object (vortex generator) is placed in the air flow, which produces a stable and continuous vortex called the Kármán vortex (Fig. 1), and the relationship between the number of cycles (frequencies) and the flow velocity of the vortex is shown in Eq. (1).

<> the constant st in the above equation is called the Strouha number. The Reynolds number is wide in relation to the representative size d of the eddy current generator (3 10 square 3 10 5 power)), and it can be seen that f is independent of the type, temperature and pressure of the object. Therefore, it can be said that the flow velocity of the fluid can be obtained by measuring the number of eddy cycles (frequency numbers) f.

During the use of an air flow meter, the gas flow is passed through the flow meter to propel the turbine blades to rotate. The number of revolutions of the impeller is directly proportional to the volume of gas passing through the air flow meter. A specially designed patented deflector is installed at the inlet of the flow meter to accelerate the flow of air into the flow meter as the flow rate increases.

The deflector frame is designed to eliminate any potential fluid disturbances such as eddy or asymmetrical flow. The push force on the turbine blades is also increased at the same time. This ensures that the flow meter is metered with high accuracy within the allowable error range, even in the case of small flow rates.

The air flow acting on the turbine blades is axial, and the turbine is mounted on the main drive shaft, which is equipped with high-strength ball bearings. After the gas passes through the turbine blades, the rotation of the turbine blades is decelerated by the gear set. The pressure in the inlet channel of the air flow meter is restored, and the channel design ensures optimal flow regime.

A triangular stainless steel needle is inserted vertically in the fluid, and the fluid will produce a vortex after passing through the steel needle, which makes the modulation frequency of the ultrasonic signal passing through the fluid meet a certain relationship with the fluid flow velocity, v=fd sThis determines the fluid flow rate.

How the crankshaft position sensor works:

There are three main types: magnetoelectric induction, Hall effect, and photoelectric. The three types work on the following principles:

1. Magnetoelectric induction:

The magnetoelectric inductive speed sensor and the crankshaft position sensor are installed in the distributor in two layers. The sensor consists of a permanent magnet induction detection coil and a rotor (timing rotor and speed rotor) that rotates with the distributor shaft. Timing rotor has.

One, two, or four teeth, etc., the speed rotor is 24 teeth. The permanent magnet induction detection coil is fixed on the distributor body. If the speed sensor signal and the crankshaft position sensor signal are known, as well as the working sequence of each cylinder, the crankshaft position of each cylinder can be known.

Rotor signal panels for magnetoelectric inductive speed sensors and crankshaft position sensors can also be mounted on crankshafts or camshafts.

2. Hall effect:

Hall-effect speed sensors and crankshaft position sensors are signal generators that utilize the Hall effect. The Hall signal generator is installed in the distributor, coaxial with the distributor head, and is fixed on the distributor panel by the encapsulated Hall chip and a permanent magnet. The number of notches on the trigger impeller is the same as the number of engine cylinders.

When the blade on the trigger impeller enters between the permanent magnet and the Hall element, the magnetic field of the Hall trigger is bypassed by the blade, and the Hall voltage is not generated, and the sensor has no output signal; When the notched part on the trigger impeller enters between the permanent magnet and the Hall element, the magnetic field lines enter the Hall element, the Hall voltage rises, and the sensor outputs a voltage signal.

3. Photoelectric type:

Photoelectric crankshaft position sensors are generally installed in distributors and consist of a signal generator and a signal disc with light holes. The signal panel rotates together with the distributor shaft photoelectric type, and there are 360 lithography gaps in the outer ring of the signal panel, which produces a signal with a crankshaft rotation angle of 1 °; Slightly inward, there are 6 orifices evenly spaced 60 ° apart, generating a signal of a 120° angle of rotation of the crankshaft, one of which is wider to generate a signal relative to the top dead center of the 1st cylinder. The signal generator is mounted on a distributor housing and consists of two light-emitting diodes, two photodiodes and a circuit.

The light-emitting diode is facing the photodiode. The signal disk is located between the light-emitting diode and the photodiode, and because there is a light hole on the signal disk, the phenomenon of alternating light transmission and shading occurs. When the beam of the light-emitting diode hits the photodiode, the photodiode generates a voltage; When the LED beam is blocked, the photodiode voltage is 0.

These voltage signals are amplified by the partial shaping of the circuit and are transmitted to the electronic control unit (ECU) at 1° and 120° crankshaft rotation angles, which calculates the engine speed and crankshaft position based on these signals.

Crankshaft position sensors are usually installed in distributors and are one of the most important sensors in control systems. Its functions are: detecting engine speed, so it is also called speed sensor; Detecting the position of the piston top dead center, so it is also called an top dead center sensor, which includes the detection of the top dead center signal of each cylinder used to control the ignition, and the top dead center signal of the first cylinder used to control the sequential fuel injection.

1. Vane air flow meter.

The structure of the air flow meter is simple and the reliability is high; However, the intake resistance is large, the response is slower and the volume is larger.

2. Carmen vortex air flow meter.

The so-called Kármán vortex refers to the vortex that occurs alternately in two columns of rotation in opposite directions downstream of the fluid when a cylindrical or triangular object is placed in a fluid.

Optical Carmen vortex air flow meter.

In the process of generating the Kármán vortex, the air pressure on both sides of the vortex generator will change, acting on the metal foil through the guide hole, so that it vibrates, when the light of the light-emitting diode is illuminated on the vibrating metal foil, the reflected light on the metal foil received by the phototransistor is the light modulated by the vortex, and its output is demodulated to obtain a frequency signal representing the air flow.

Ultrasonic Kármán vortex air flow meter.

Ultrasonic emission probes and receiver probes are mounted opposite each other on both sides of the downstream tubing of the Kármán eddy current generator. Due to the influence of Kármán vortex on air density, the ultrasonic wave will be sent from the transmitting probe to the receiving probe later than the non-vortex probe, resulting in phase difference. By processing this phase signal, you can get a vortex pulse signal, and a first-class air flow meter.

1 How it works.

When there is no air flow, the bridge is in equilibrium, and the control circuit outputs a certain heating current to the first resistance rh; When there is air flowing, because the heat of RH is absorbed by the air and becomes cold, its resistance value changes, the bridge is out of balance, if the temperature difference between the resistance and the inhaled air is kept unchanged and a certain value, it is necessary to increase the current flow through the resistance IH. Therefore, the current IH is a function of the air quality flow.

4. Hot film air flow meter.

The working principle of the hot film air flow meter is similar to that of the ** type air flow meter, which works with the Wheatstone bridge. The difference is that the hot film type does not use platinum wire as the first grade, but makes the first resistor, compensation resistor and bridge resistor on the same ceramic substrate with a thick film process.

f=st v d(1).

d. Representative dimensions of a cylindrical object.

v The flow rate of a fluid.

f is the number of vortex cycles.

1. Introduction to air flow meter.

The role of the air flow meter.

The air flow meter measures the amount of fresh air entering the engine intake manifold and the intake air temperature, and the ECU uses this information to make injection corrections, smoke limits, and EGR opening control.

2.Installation location.

The sensor is mounted on the engine intake duct and at the rear end of the air filter.

3.How it works.

The principle of an air flow meter.

The air flow sensor is to integrate some electronic components on a ceramic substrate, when the engine is working normally, the diaphragm is first heated, and the fresh air flows through the sensor will take away part of the heat, at this time the ECU will control the Wheatstone bridge on the diaphragm to supplement the diaphragm, which will cause a change in the electrical signal, when the signal is transmitted to the ECU, the ECU will calculate the air intake according to this change.

The principle of the air temperature sensor.

The inlet air temperature sensor is a negative temperature coefficient resistor, when the inlet air temperature changes, the resistance value of the resistor will change, causing a change in the signal voltage at the ECU terminal, and the ECU calculates the inlet air temperature based on this change.

Determination of the direction of the airflow.

There is a same temperature resistance at both ends of the hot film of the air flow meter, and when the air flow flows through the hot film, it will take away part of the heat, so the temperature at the front end of the hot film is lower than the temperature at the rear end, and the ECU judges the direction of the air flow according to this signal!

4.Wiring diagram of an air flow meter.

5.Control policy.

The ECU will monitor the working condition of the air flow meter at all times, and when the ECU judges that the air flow meter is faulty, it will take corresponding control, as follows.

The engine mil light is lit, the EGR system is withdrawn from work, and the exhaust gases will no longer participate in the system work;

The engine speed will be limited to a certain speed, and the power will be limited;

When the air flow meter fails, the engine start is not affected and can be started normally;

Second, the detection of air flow meter:

Fault codes related to air flow meters

When the air flows through the Kármán vortex generator, the rear part of the Kármán vortex will continue to produce the Kármán vortex, and the number of Kármán vortices generated in a unit time (the frequency of occurrence) is related to the speed of the air flow, as long as the frequency of the Kármán vortex is measured, the size of the air flow can be known.

Turbine flowmeter and precession.

Vortex flowmeter.

None of them are the Kármán principle, the working principle of the Suco turbine flowmeter is that fluid flows through the turbine.

Flow meter sensors.

When the shell is in the shell, because the blade of the impeller has a certain angle with the flow direction of the fluid, the impulse of the fluid makes the blade have a rotating torque, which is overcome.

Frictional moment. and fluid resistance.

After the blades rotate, in.

Moment balancing. The rear speed is stable, and under certain conditions, the speed is proportional to the flow rate, due to the blades.

magnetic permeability, which is in the signal detector (by permanent.

The magnetic field is composed of a magnet and a coil, and the rotating blades cut the magnetic field lines, periodically changing the coil.

magnetic flux, so that both ends of the coil are induced.

The electrical pulse signal is amplified and shaped by the amplifier to form a continuous signal with a certain amplitude.

Rectangular pulses. waves, which can be transmitted far away.

The display gauge shows the instantaneous flow of the fluid with.

Cumulative traffic. The principle of Suke precession vortex flowmeter is to place a set of spiral guide vanes on the inlet side of the flowmeter when the fluid enters.

Flow sensors.

, the guide vanes force the fluid to produce a violent vortex current. When the fluid enters the diffusion section, the vortex flow begins to rotate twice under the action of reflux, forming a gyro-type vortex precession phenomenon, and the precession frequency is proportional to the flow rate and is not affected.

Physics of Fluids. properties and densities affect the detection of components.

Measuring the precession frequency of the secondary rotation of the fluid can obtain better results in a wide range of flow rates.

Linearity. Signal warp.

Preamplifier.

Amplification, filtering, and shaping are proportional to the flow rate.

The pulse signal is then sent to the microprocessor together with the detection signal such as temperature and pressure for accumulation processing, and finally in the .

LCD screen.

The measurement results are displayed on .

Instantaneous flow, cumulative flow, temperature, pressure, etc.).

It's not the same thing. Here's why: A precession vortex flowmeter is a type of flow meter that specializes in measuring gases.

The main structure consists of a venturi measuring tube, a front starter, a rear rectifier, a sensing head, and a temperature and pressure assembly. The vortex flowmeter generally refers to the vortex flowmeter. Gases, vapors and liquid media can be measured.

It is a flow meter that uses the Karmen vortex principle. The main structure consists of a circular measuring tube, a vortex generator (triangular, cylindrical, etc.), a sensing head, and a temperature and pressure component. Professional manufacturer of flow (thermal) meters, welcome**. ~~