Soway Pressure Sensor Working Principle

Pressure sensors are the most widely used sensors in industrial automation. There are mainly strain gauge pressure sensors, ceramic pressure sensors, diffusion silicon pressure sensors, sapphire pressure sensors, piezoelectric pressure sensors, etc., which are widely used in various industrial self-control environments, involving water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, Military, petrochemical, oil well, electric power, ships, machine tools, pipelines and many other industries.

1. Principle and application of ceramic pressure sensor

The corrosion-resistant ceramic pressure sensor has no liquid transfer, the pressure acts directly on the front surface of the ceramic diaphragm, causing a slight deformation of the diaphragm. The thick film resistor is printed on the back of the ceramic diaphragm and connected into a Wheatstone bridge. Bridge), due to the piezoresistive effect of the varistor, the bridge produces a highly linear voltage signal proportional to the pressure, which is proportional to the excitation voltage. The standard signal is calibrated to 2.0 / 3.0 / 3.3 depending on the pressure range. mV/V, etc., compatible with strain gauge sensors.

2. Principle and application of strain gauge pressure sensor

There are many types of mechanical sensors, such as resistance strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, inductive pressure sensors, capacitive pressure sensors, resonant pressure sensors and capacitive acceleration sensors. But the most widely used is a piezoresistive pressure sensor, which has a very low price, high precision and good linearity.

When we understand the piezoresistive force sensor, we first understand the components of the resistance strain gauge. A strain gage 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. The metal resistance strain gauge has two kinds of filament strain gauges and metal foil strain gauges. Usually, the strain gauge is tightly bonded to the mechanical strain matrix by a special adhesive. When the stress changes due to the force of the substrate, the strain gauges are also deformed together, so that the resistance of the strain gauge is changed, thereby The voltage applied to the resistor changes. Such strain gauges typically have a small change in resistance when stressed. Typically, such strain gauges form a strain bridge and are amplified by a subsequent instrumentation amplifier and transmitted to the processing circuitry (usually A/D conversion). And CPU) display or actuator.

It is a schematic structural view of a strain gauge, which is composed of a base material, a metal strained wire or a strained foil, an insulating protective sheet and a lead wire.

Depending on the application, the resistance of the strain gauge can be designed by the designer, but the range of resistance should be noted: the resistance is too small, the required drive current is too large, and the heat of the strain gauge causes the temperature to be too high. Used in different environments, the resistance value of the strain gauge is changed too much, the output zero drift is obvious, and the zero adjustment circuit is too complicated. The resistance is too large, the impedance is too high, and the ability to resist external electromagnetic interference is poor. Generally, it is about tens of euros to several tens of kiloohms.

The working principle of the resistance strain gauge

The working principle of the metal resistance strain gauge is a phenomenon in which the strain resistance adsorbed on the base material changes with the mechanical deformation, which is commonly called the resistance strain effect. The resistance value of the metal conductor can be expressed by the following formula:

In the formula:

Ρ——resistivity of metal conductor (Ω.cm2/m)

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

L - the length of the conductor (m)

Taking 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 subjected to an external force. When it is stretched, 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 is decreased and the section is increased, and the resistance value is decreased. As long as the change in resistance is measured (usually the voltage across the measured resistance), the strain of the strained wire is obtained.