Views: 0 Author: Site Editor Publish Time: 2023-02-02 Origin: 粉体圈儿
Ceramic pressure sensor is a piezoresistive pressure sensor made of special ceramic materials and refined by special process. Ceramic is a recognized material with high elasticity, resistance to corrosion, wear, impact and vibration. Ceramic thermal stability and thick film resistance can make it work in a temperature range of -40℃ ~ 125℃, and has high precision measurement, high stability. Electrical insulation degree is greater than 2KV, strong output signal, good long-term stability. Ceramic sensors with high characteristics and low price will be the development direction of pressure sensors. In Europe and the United States, ceramic sensors have a trend of replacing other types of sensors comprehensively. In China, more and more users are using alternative diffused silicon pressure sensors.
① Ceramic capacitive pressure sensor Ceramic capacitive pressure sensor is made of fixed ceramic base and movable ceramic diaphragm structure, movable diaphragm through glass paste and other ways to seal together with the base. The inner printed electrode pattern between the two forms a variable capacitance. When the dielectric pressure on the diaphragm changes, the capacitance between the two changes, and the signal is converted and adjusted through the conditioning chip and output to the rear stage. Ceramic capacitor technology has the advantages of moderate cost, wide range, good temperature characteristics, consistency and long-term stability.
Because the edge of the ceramic diaphragm is fixed on the ceramic base and the periphery is supported, the middle deformation is large and the edge deformation is small during the stress, and the capacitance is nonlinear and the sensitivity is reduced. In order to reduce the influence of temperature and edge effect, a circular single electrode is arranged on the ceramic diaphragm as a common electrode, and two electrodes are arranged on the ceramic cover plate to make the area equal, forming a coaxial ring double capacitance sensor.
The center is the measuring capacitor Cp, the edge ring is the reference capacitor Cr, and the outside of Cr is the fixed support edge. The subsequent signal conditioning circuit deals with the pressure difference between the two capacitors. Square wave excitation signal is used to convert the variation of Cp and Cr into DC voltage output respectively. The applied pressure is measured by the difference signal of the two output voltages. The dual capacitance structure greatly reduces the nonlinear error of the sensor system. At the same time, when the ambient temperature changes, because the two capacitors feel the same temperature change, the temperature effect on them is consistent, which cancels out the measurement error brought by the temperature change and realizes the function of temperature self-compensation.
Ceramic capacitive pressure sensor can be widely used in water, gas and liquid pressure detection due to its advantages of corrosion resistance, impact resistance, no hysteresis, strong compatibility of media, especially suitable for the harsh environment of automotive systems. Aiming at the emerging application market of pressure sensors such as the Internet of Things and home appliances, the advantages of ceramic capacitive shock resistance can be applied to the water pressure measurement of water supply network to perfectly cope with the water hammer effect. For variable pressure cooker applications, the ceramic capacitor flat film structure can avoid clogging.
② ceramic piezoresistive pressure sensor
Ceramic piezoresistive pressure sensor is mainly composed of ceramic ring, ceramic diaphragm and ceramic cover plate. The ceramic diaphragm is a force sensitive elastic body, and the thick film technology is used to form a Whiston bridge as the circuit of the sensor. Due to the piezoresistive (deformation) effect of the resistance, the voltage signal is generated.
The thick film resistor is printed on the back of the ceramic diaphragm and connected to form a Wheatstone bridge (closed bridge). When the pressure is zero, the bridge is in equilibrium and the output voltage is zero; When the pressure is applied to the bridge, the diaphragm deformation causes the resistance values of the four resistors of the bridge to change, and the bridge is in an unbalanced state, producing a voltage signal that is highly linear and proportional to the pressure and also proportional to the excitation voltage. A voltage signal is generated due to the piezoresistive (deformation) effect of the resistance. The standard signal is calibrated as 2.0/3.0/3.3mV/V according to the different pressure range, which can be compatible with the strain sensor. Through laser calibration, the sensor has high temperature stability and time stability, the sensor comes with temperature compensation of 0 ~ 70℃, and can be directly contacted with most media.
