With the development of the engine and the progress of science and technology, electronically controlled common rail scheme has become the mainstream line of the engine market, rail pressure sensor, oil pressure sensor, intake pressure temperature sensor has become the engine operation of the necessary sensors. With the application and popularization of the engine health management system, the physical parameters of the engine system need to be accurately detected and controlled. More pressure sensors are applied in the new generation of engines. These sensors not only require high precision, fast response time, but also ensure the reliability and stability of the whole life cycle of pressure sensor.
Automotive Pressure technology (APT) uses ceramic capacitors as sensing units, which are mainly composed of ceramic substrate, ceramic diaphragm, metal electrode and glass sealant.
When the pressure on the ceramic membrane, ceramic diaphragm deformation occurred due to external force, up and down between two metal electrodes gap d changes, according to the capacitive formula can be seen that the capacity value of ceramic capacitor because of the change of gap change, change of capacitance value again after adjusting circuit processing, converted into a voltage signal, pressure and voltage curve is obtained.
From the point of principle of ceramic capacitors, capacitance changes represent the change of pressure, regulate circuit is to identify the minimum capacitance value is the precision of the sensor, in order to ensure the accuracy of the sensor is higher, the change of capacitance value range to change in a reasonable range, is adjusting circuit can identify to the already, and accurate identification of changes to the capacitance value size.
For ceramic capacitive sensors with different pressure ranges, the change range of electrode gap D in the pressure working range is guaranteed to be certain, so it is necessary to select the appropriate thickness of ceramic diaphragm according to the measurement pressure, that is to say, the thickness of ceramic diaphragm determines the measurement pressure. The thicker the ceramic diaphragm is, the greater the pressure it can bear, which can reach 15MPa; the thinner the ceramic diaphragm is, the more sensitive it is to low pressure, and the pressure can be measured at a minimum of 20K Pa. However, the thinner the ceramic diaphragm is, the process is difficult, the cost is relatively high, and the cost performance is not high compared to the MEMS sensor.