Vane air flow meter

The air flow meter has a simple structure and high reliability; however, it has large air intake resistance, slow response and large volume

Karman vortex air flow meter The so-called Karman vortex refers to when a cylindrical or triangular object is placed in the fluid, two rows of vortices that rotate in opposite directions and appear alternately will be generated downstream of the object

Optical Karman Vortex Air Flow Meter

In the process of generating Karman vortex, the air pressure on both sides of the vortex generator will change and act on the metal foil through the guide hole, causing it to vibrate. , when the light of the light-emitting diode shines on the vibrating metal foil, the reflected light on the metal foil received by the photosensitive triode is the light modulated by the vortex, and its output is demodulated to obtain a frequency signal representing the air flow.

Ultrasonic Karman vortex air flow meter

Usonic transmitting probe and receiving probe are installed oppositely on both sides of the pipeline downstream of the Karman vortex generator. Due to the influence of Karman vortex on air density, the time of ultrasonic wave from transmitting probe to receiving probe will be later than that without vortex, resulting in a phase difference. By processing this phase signal, the vortex pulse signal can be obtained.

Working principle of hot-wire air flow meter

When there is no air flow, the bridge is in a balanced state and the control circuit output A certain heating current flows to the hot wire resistor RH; when there is air flow, because the heat of RH is absorbed by the air and becomes cold, its resistance value changes, and the bridge loses balance. If the temperature difference between the hot wire resistor and the inhaled air remains unchanged and is To a certain value, the current IH flowing through the hot wire resistor must be increased. Therefore, the hot wire current IH is a function of the air mass flow rate.

Hot Film Air Flow Meter

The working principle of the hot film air flow meter is similar to that of the hot-wire air flow meter, both of which use a Wheatstone bridge. The difference is that the hot film type does not use platinum wire as the hot wire, but uses the thick film process to make the hot wire resistor, compensation resistor and bridge resistor on the same ceramic substrate.

Target air flow meter

When the air flows in the measuring tube, its own kinetic energy creates a pressure difference with the target, which generates a force on the target, causing the The target produces a slight displacement, and the force is proportional to the square of the medium flow rate. The mathematical formula is:

F = Cd·A·ρ·V2/2

F :The force exerted on the target film

Cd: Fluid resistance coefficient

A: The axial projection area of ??the target film on the measuring tube

ρ: Under working conditions Medium Density

V: Characteristic flow velocity of air in the measuring tube

The force exerted on the target is transmitted through the target rod, causing slight changes in the elastomer of the sensor, which are converted by the circuit , output the corresponding electrical signal.