Application of Air Pressure Sensor in Automobile Tire

Air pressure sensor

1) Energy and principle: It is mainly a sensor used to detect air pressure.In the middle of the silicon wafer, a square diaphragm is formed by etching from the back side, and the diaphragm is used to convert the pressure into stress,On the surface of the diaphragm, four p-type measuring resistors are formed by diffusing impurities, and they are connected in a bridge circuit. The stress applied to the diaphragm is converted into a change in resistance by using the piezoresistive effect. After the circuit, between the two output ends of the bridge circuit, the output is output in the form of a potential difference.

2Tire pressure measurement and circuit design

The application of air pressure sensor in automobile tires is described in detail by taking the measurement of tire air pressure as an example.This design can be made into a portable device. When measuring, the gauge of the air pressure sensor is placed on the tire valve. At this time, the tire pressure acts on the diaphragm of the sensor, and a weak voltage signal is output through the piezoresistive effect and series transformation. , process the voltage signal accordingly to display the voltage value.It can be seen that different air pressures correspond to different voltage values, that is, the air pressure values and voltage values are in one-to-one correspondence, thus indirectly measuring the air pressure value.

2.1 Mutual conversion of air pressure value and voltage value

Any type of tire has its standard air pressure. The standard air pressure of a certain type of tire is that the P0 pressure exceeds the P1 high pressure, and the lower pressure is the P2 pressure.After this device shows a certain voltage value V0, when the pressure is P1 high voltage, it shows V1, and when it reaches the low voltage state P2, it shows V2. The strength of the air pressure is reflected in the voltage value through this device. When the voltage value is between V1- When changing within the range of V2, the air pressure is in line with the standard.If the voltage value is higher than V1, it is a high pressure state, and if it is lower than V2, it is a low pressure state. At this time, a series of measures should be taken to change the tire pressure value within the standard range, so as to protect the tire.

2.2 Voltage signal amplifier circuit

The high-precision low-noise instrument amplifier AD620 we selected can be used in amplifiers with small output signals of sensors, such as photocell sensors, strain gauge sensors and pressure sensors.Because of its low noise, high gain accuracy, small gain temperature coefficient and high linearity and other excellent performance. Ideal for use in this system.AD620 is an instrumentation amplifier that can be set to a magnification of 1-1000 with only one external resistor. It has good DC performance and AC performance. The small size and low power consumption of AD620 have become important factors in the application of pressure sensors.

2.3 Digitization and display of voltage signals

The amplified analog voltage is converted from analog to digital through A/D converter. The A/D conversion result is converted into 7-segment decoding through the counting and decoding circuit, and finally the drive displays the corresponding value.

The dual-integration A/D converter MC14433 is selected to form a 31/2 digital voltage display, and the dynamic scanning display is used to display multiple modulated BCD code output and over-range output terminals, which is convenient for automatic control.MC1413 is an integrated circuit driver, which contains 7 inverting drive units, each unit adopts Darlington transistor circuit. CC4511 is a 7-segment decoding driver. MC14433 provides a reference voltage with adjustable output. When the reference voltage is a certain value, the output voltage range is a fixed value.

3. Conclusion

The application of automobile pressure sensors in tires is constantly improving, and there are many ways, such as the use of radio transmission and reception to measure the level of air pressure.The variety of automotive pressure sensors is constantly increasing, and the functions are constantly improving. Generally speaking, switch-type sensors are gradually replaced by linear pressure sensors, ordinary ones are gradually replaced by high-performance and multi-functional sensors, and analog pressure sensors are gradually replaced by digital sensors and intelligent sensors.