Pressure sensor working principle and application

Strain gauge type pressure sensor principle and application range <br> <br> mechanical sensor, such as pressure sensors strain gauges, semiconductor strain gauge pressure sensor, a piezoresistive pressure sensor, an inductive pressure sensor, a capacitive pressure sensor, resonant Pressure sensors and capacitive acceleration sensors. But the most widely used is the piezoresistive pressure sensor, which has a very low price, high accuracy and good linearity. Below we mainly introduce such sensors.

In understanding the piezoresistive force sensor, we first understand the element resistance strain gauge. The resistance strain gauge is a sensitive device that converts the strain change on the device under test into an electrical signal. It is one of the main components of a piezoresistive strain sensor. The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. Metal strain gauges are also available in wire strain gauges and metal foil strain gauges. Usually, the strain gauges are tightly bonded to a mechanical strain matrix through a special adhesive agent. When the stress of the base body changes, the strain gauges also deform together, so that the resistance of the strain gauges is changed. The voltage applied to the resistor changes. These strain gauges usually have a small change in resistance when they are subjected to stress. In general, these strain gauges form a strain bridge and are amplified by a subsequent instrumentation amplifier and transmitted to a processing circuit (usually A/D conversion). And CPU) display or actuator.

The working principle of resistance strain gauge metal <br> <br> resistance strain gauge is a strain resistance adsorption phenomena on the substrate material with mechanical deformation generated by change in the resistance, commonly known as resistance strain effect. The resistance of a metal conductor can be expressed by the following formula:

In the formula: ρ——Resistivity of metal conductor (Ω·cm2/m)

S - cross-sectional area of ​​the conductor (cm2)

L——length of conductor (m)

We take the wire strain resistance as an example. When the wire is subjected to an external force, its length and cross-sectional area will change. It can be easily seen from the above formula that the resistance value will change if the wire is affected by external force. When extended, its length increases, and the cross-sectional area decreases, and the resistance value increases. When the wire is compressed by an external force, the length decreases and the cross section increases, and the resistance value decreases. As long as the measured increase in the resistance change (usually measure voltage across the resistor), the strain can be obtained the wire strain situation 2, ceramic pressure sensor principle and application <br> <br> corrosion resistant ceramic pressure sensor is not liquid Transfer, the pressure acts directly on the front surface of the ceramic diaphragm, causing the diaphragm to produce a slight deformation. The thick film resistor is printed on the back of the ceramic diaphragm and is connected to a Wheatstone bridge (closed bridge) due to the varistor pressure. The resistive effect causes the bridge to produce a highly linear voltage proportional to the pressure and a voltage signal proportional to the excitation voltage. The standard signal is calibrated to 2.0/3.0/3.3 mV/V, depending on the pressure range, and can be strained. Sensors are compatible. Through laser calibration, the sensor has high temperature stability and time stability, the sensor comes with temperature compensation 0 ~ 70 °C, and can be in direct contact with most of the media.

Ceramics is a well-known material with high elasticity, corrosion resistance, wear resistance, impact resistance and vibration. The thermal stability of ceramics and its thick film resistance can make its operating temperature range up to -40 ~ 135 °C, but also has high accuracy and high stability. Electrical insulation >2kV, strong output signal, good long-term stability. High-performance, low-cost ceramic sensors will be the development direction of pressure sensors. In Europe and the United States, there is a trend to replace other types of sensors. In China, more and more users use ceramic sensors instead of diffusion silicon pressure sensors.

3, pressure diffuser silicon pressure sensor principle and application <br> <br> measured media works directly on the sensor diaphragm (stainless steel or ceramic), the diaphragm to produce micro-displacement is proportional to the medium pressure, so that The resistance of the sensor changes, and this change is detected by an electronic circuit and a standard measurement signal corresponding to this pressure is converted and output.

4. Principle and Application of Sapphire Pressure Sensor <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> Sapphire Pressure Sensor Principle

Sapphire is composed of single-crystal insulator elements that do not suffer from hysteresis, fatigue, and creep; sapphire is stronger and harder than silicon, and is not afraid of deformation; sapphire has very good elasticity and insulation properties (up to 1000 OC). Silicon-sapphire semiconductor sensing devices are insensitive to temperature changes and have good operating characteristics even at high temperatures; sapphire has extremely strong radiation resistance; in addition, silicon-sapphire semiconductor sensitive devices have no pn drift. Therefore, the manufacturing process is fundamentally simplified, the repeatability is improved, and a high yield is ensured.

Pressure sensors and transmitters manufactured with silicon-sapphire semiconductor sensing elements can operate normally in the harshest operating conditions, with high reliability, accuracy, minimal temperature error, and cost-effectiveness.

Gauge pressure sensors and transmitters consist of two diaphragms: a titanium alloy diaphragm and a titanium alloy diaphragm. The sapphire sheet printed with a heteroepitaxial strain-sensitive bridge circuit was welded on a titanium alloy measurement diaphragm. The measured pressure is transmitted to the receiving diaphragm (the receiving diaphragm is firmly connected with the measuring diaphragm by a tie rod). Under the effect of pressure, the titanium alloy receives the deformation of the diaphragm. After the deformation is perceived by the silicon-sapphire sensor, the output of the bridge will change, and the amplitude of the change is proportional to the measured pressure.

The circuit of the sensor can guarantee the power supply of the strain bridge circuit, and convert the unbalanced signal of the strain bridge into a unified electrical signal output (0-5, 4-20mA or 0-5V). In the absolute pressure sensor and transmitter, the sapphire sheet is connected with the solder of the ceramic base glass and functions as an elastic element. The measured pressure is converted into strain gauge deformation to achieve the purpose of pressure measurement.

5. Principles and Applications of Piezoelectric Pressure Sensors <br><br> Piezoelectric Pressure Sensors Mainly used piezoelectric materials include quartz, sodium potassium tartrate and dihydrogen phosphate. Among them, quartz (silicon dioxide) is a kind of natural crystal. The piezoelectric effect is found in this kind of crystal. Within a certain temperature range, the piezoelectricity is always there, but after the temperature exceeds this range, the piezoelectricity is completely Disappear (this high temperature is the so-called "curie point"). Because the electric field changes little with the change of stress (that is, the piezoelectric coefficient is relatively low), quartz is gradually replaced by other piezoelectric crystals. Potassium sodium tartrate has a large piezoelectric sensitivity and piezoelectric coefficient, but it can only be applied in environments with low room temperature and low humidity. Dihydrogen phosphate is an artificial crystal that can withstand high temperatures and high humidity, so it has been widely used.

Now the piezoelectric effect is also applied to polycrystals, such as current piezoelectric ceramics, including barium titanate piezoelectric ceramics, PZT, niobate piezoelectric ceramics, lead magnesium niobate piezoelectric ceramics, and the like.

Piezoelectric effect is the main working principle of piezoelectric sensor. Piezoelectric sensor cannot be used for static measurement because the charge after external force is only saved when the loop has infinite input impedance. The actual situation is not like this, so this determines that the piezoelectric sensor can only measure the dynamic stress.

Piezoelectric sensors are mainly used in the measurement of acceleration, pressure, and force. Piezoelectric acceleration sensor is a commonly used accelerometer. It has the advantages of simple structure, small size, light weight and long service life. Piezoelectric accelerometers have been widely used in the vibration and shock measurement of aircrafts, automobiles, ships, bridges, and buildings, especially in the aviation and aerospace fields. Piezoelectric sensors can also be used to measure the internal combustion pressure measurement and vacuum measurement. It can also be used in the military industry, for example, to measure the momentary pressure change of a shotgun bullet fired in a raft and the shock pressure of the muzzle. It can be used to measure large pressures, but it can also be used to measure tiny pressures.

Piezoelectric sensors are also widely used in biomedical measurements. For example, ventricular catheter microphones are made of piezoelectric sensors. Because measuring dynamic pressure is so common, the application of piezoelectric sensors is very extensive.