Frequently
Asked
Questions
The piezoresistive pressure sensor is formed by utilizing the piezoresistive effect of single crystal silicon.
The single crystal silicon chip is used as the elastic element, and the integrated circuit technology is used on the single crystal silicon diaphragm. Diffusion of a group of equal-value resistors in a specific direction of single crystal silicon. Connect the resistors into a bridge. , the monocrystalline silicon wafer is placed in the sensor cavity.
When the pressure changes, the single crystal silicon strains. The strain resistance directly diffused on it produces a change proportional to the measured pressure. Then the corresponding voltage output signal is obtained by the bridge circuit.
When the sensor is in the pressure medium, the medium pressure acts on the corrugated diaphragm. The silicone oil in it is under pressure.
Silicone oil senses the pressure of the diaphragm to the semiconductor core. After being pressed, its resistance value changes, and the resistance signal is drawn out through the lead wire.
The stainless steel bellows diaphragm housing senses the pressure and protects the core. Therefore, piezoresistive pressure sensors can sense pressure signals in corrosive media.
A piezoresistive pressure sensor is generally connected to a Wheatstone bridge through leads.
Normally, the sensitive core has no external pressure, and the bridge is in a balanced state (called zero position). When the chip resistance changes after the sensor is pressed, the bridge will lose its balance.
If a constant current or voltage power supply is added to the bridge, the bridge will output a voltage signal corresponding to the pressure. In this way, the resistance change of the sensor is converted into a pressure signal output through the bridge.
Appearing in most pressure sensors, the method of manufacturing integrated circuits is used to form four resistance strips with equal resistance values, and connect them to form a Wheatstone bridge.
The Wheatstone bridge uses constant current power supply, so that the output of the bridge is not affected by temperature, and the Wheatstone bridge detects the change of the resistance value. After being amplified by the output amplifier. After the conversion of voltage and current, it is converted into a corresponding current signal.
The current signal is compensated by a non-linear correction loop. That is to say, a standard output signal of 4~20mA is generated in which the input voltage has a linear corresponding relationship.
Applications of piezoresistive pressure sensors:
- Aerospace engine test system;
- Hydraulic, marine, diesel engine industries;
- Medicine, biochemistry, fermentation detection system;
- Automatic control and detection system;
Most pressure sensors currently installed in the field are based on MEMS technology and utilize piezoresistive or capacitive measurement principles.
Measuring principle of capacitive sensor technology:
Two parallel and electrically isolated conductive plates are required for effective operation of capacitive pressure sensors. The bottom plate is fixed, while the top is sensitive to pressure changes. When pressure is applied, the top plate (or membrane) flexes and develops a capacitance Δ. This change in capacitance is then converted into an electrical signal that can be read and regulated by an ASIC or microcontroller.
Technical comparison of piezoresistive and capacitive sensors:
Capacitive pressure sensors have many advantages over piezoresistive sensors. Although they may require more complex signal conditioning circuits and calibration algorithms. But they have higher precision and lower total error band.
Additionally, capacitive pressure sensors have low power consumption. Because due to its nature, no DC current flows through the sensor element. Therefore, very low-power sensing systems can be designed and implemented. Only a small bias to the circuit is required from the external reader. making it ideal for remote or implantable medical applications.
