The meter coefficient of the air flow sensor is not affected by the physical properties of the measurement medium, and can be generalized to other mediums by a typical medium. However, due to the large difference in the flow rate range of liquid and gas, the frequency range also varies greatly. In the amplifier circuit that processes vortex signals, the passband of the filter is different, and the circuit parameters are also different. Therefore, the same circuit parameter cannot be used to measure different media. Different types of air flow sensors have different types of composition:
1. The valve-type air flow sensor is installed on the gasoline engine and is installed between the air filter and the throttle valve. Its function is to detect the air intake of the engine, and convert the detection result into an electrical signal, and then input it into the microcomputer. The sensor is composed of an air flow meter and a potentiometer.
2. Kaman vortex air flow sensor: In order to overcome the shortcomings of the valve type air flow sensor, that is, on the premise of ensuring the measurement accuracy, the measurement range is expanded, and the sliding contact is eliminated, and a small and light air flow sensor has been developed. That is, Kaman vortex air flow sensor. Karman vortex is a physical phenomenon. The detection method and electronic control circuit of the vortex have nothing to do with the detection accuracy. The air passage area and the size of the vortex column change the detection accuracy. And because the output of this sensor is an electronic signal (frequency), so when the signal is input to the control circuit of the system, the AD converter can be omitted. Therefore, from an essential point of view, the Kaman vortex air flow sensor is suitable for signals processed by a microcomputer. This sensor has the following three advantages: high test accuracy, linear signal output, and simple signal processing; long-term use, performance will not change; because it is to detect volume flow, there is no need to modify the temperature and atmospheric pressure.
3. Temperature and pressure compensation air flow sensor, mainly used for flow measurement of industrial pipeline medium fluid, such as gas, liquid, steam and other media. It is characterized by small pressure loss, large measuring range and high accuracy. It is hardly affected by parameters such as fluid density, pressure, temperature, viscosity, etc. when measuring volume flow under operating conditions. No moving mechanical parts, so high reliability and low maintenance. Instrument parameters can be stable for a long time. This instrument adopts piezoelectric stress sensor, which has high reliability and can work within the operating temperature range of -10℃～+300℃. There are analog standard signals and digital pulse signal outputs, which are easy to use with digital systems such as computers. It is a relatively advanced and ideal flow rate.