The vortex flowmeter

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What is the working principle of the Karman vortex air flow meter? The air flow meter is a key component of the engine management system, used to detect the quality of air entering the engine. The blade type air flow meter has a simple and reliable structure, but it has disadvantages such as high intake resistance, slow response, and large volume. The Karman vortex air flow meter generates two columns of alternating vortices with opposite rotation directions by placing cylindrical or triangular objects in the fluid, known as Karman vortices. The optical Karman vortex air flowmeter utilizes the change in air pressure on both sides of the vortex generator, and the guide hole acts on the metal foil to make it vibrate. The light from the light-emitting diode shines on the vibrating metal foil, and the photosensitive transistor receives the reflected light, which is modulated by vortices and outputs a frequency signal representing the air flow rate after demodulation. The ultrasonic Karman vortex air flowmeter is equipped with ultrasonic transmission probes and reception probes on both sides of the downstream pipeline of the Karman vortex generator. Due to the influence of Karman eddy currents on air density, the time for ultrasonic waves to travel from the transmitting probe to the receiving probe becomes later, resulting in a phase difference. By processing the phase signal, the vortex pulse signal can be obtained. The working principle of a hot wire air flow meter is that when there is no air flow, the bridge is in a balanced state, and the control circuit outputs a heating current to the hot wire resistor. If there is air flow, the hot wire resistor absorbs heat and cools down, causing the resistance value to change and causing the bridge to lose balance. It is necessary to increase the current flowing through the hot wire resistor to maintain a constant temperature difference with the inhaled air. This current is a function of the air mass flow rate. The working principle of the hot film air flow meter is similar to that of the hot wire type, both of which are based on the Wheatstone bridge. The difference is that the hot film type does not use white gold wire as the hot wire, but instead uses thick film technology to fabricate the hot wire resistor, compensation resistor, and bridge resistor on the same ceramic substrate.

2. Working principle of vortex flowmeter

The flow profile of the flow sensor is similar to the profile of a Venturi tube.

. Place a set of spiral guide vanes on the inlet side, which force the fluid to generate intense vortex flow when it enters the flow sensor. When the fluid enters the diffusion section, the vortex flow is subjected to backflow and begins to undergo secondary rotation, forming a gyroscopic vortex precession phenomenon. The precession frequency is proportional to the flow rate and is not affected by the physical properties and density of the fluid. By measuring the secondary rotation precession frequency of the fluid with the detection element, good linearity can be obtained over a wide range of flow conditions. The signal is amplified, filtered, shaped, and converted into a pulse signal proportional to the flow rate by a pre roll amplifier, and then sent to the microprocessor for integration processing along with temperature, pressure, and other detection signals. Finally, the measurement results (instantaneous flow rate, cumulative flow rate, temperature, pressure data) are di

2. Working principle of vortex flowmeter

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