Pressure sensors operate on a simple mechanical principle: deformation of an elastic element causes changes in resistance, capacitance, or inductance, thereby changing the electrical signal. The elastic element of a pressure sensor is typically made of metal or polymer material and senses changes in external pressure, then deforms. When external pressure is applied to the sensor, the elastic element deforms and produces a corresponding effect. For example, its resistance changes, or its capacitance and inductance change proportionally with the pressure.
Main uses:
1. In the field of industrial automation, pressure sensors are used to measure pressure, calculate pressure changes to regulate pressure, and output pressure change data. They are an important component of industrial automatic control, automatic testing, and intelligent analysis systems.
2. Pressure sensors can also be used as control, measurement and regulation parameters in hydraulic systems to control the stroke and speed of blades and hydraulic actuators, as well as for safety and energy-saving control of various types of hydraulic systems.
3. Pressure sensors can be used as control, measurement, and regulation parameters in traffic systems to improve traffic flow, reduce energy consumption, and enhance safety.
4. In marine engineering, pressure sensors can measure ocean pressure to study ocean dynamics and improve the safety and efficiency of the fisheries industry.
5. Pressure sensors can be used as control, measurement, and regulation parameters in environmental and safety systems for indoor and outdoor pressure measurement, measuring air pollutants and meteorological changes, thereby improving environmental safety and energy efficiency.
Based on the above principles, pressure sensors are generally classified into three types: resistive, capacitive, and inductive. Among them, resistive pressure sensors are the most common, detecting pressure by utilizing changes in resistance. Capacitive pressure sensors detect pressure by utilizing changes in capacitance, while inductive pressure sensors detect pressure by utilizing changes in inductance.
The working principle of a resistance pressure sensor is based on the dependence of the material's resistivity, temperature, and yield strength. When an isotropic material is subjected to force at both ends of a certain length, it deforms and elongates, but remains stable within a linear range. Due to its corresponding material properties, its resistance value changes accordingly with the change in pressure.
Capacitive pressure sensors operate on a different principle than inductive pressure sensors. Capacitive pressure sensors detect changes in the capacitance of their sensing area. Inductive pressure sensors detect changes in magnetic flux. Both types of sensors are more accurate than resistive pressure sensors, but they are relatively more expensive, larger, and require more maintenance due to the more complex circuitry and manufacturing processes involved.
The piezoelectric effect is the main working principle of piezoelectric sensors. Piezoelectric sensors cannot be used for static measurements because the charge generated after an external force is applied is only preserved when the circuit has infinite input impedance. This is not the case in reality, which means that piezoelectric sensors can only measure dynamic stress.
Pressure sensors consist of a sensitive element, a conversion element, and a subsequent processing section. They typically use strain gauges to measure pressure. The manufacturing principle of strain gauges is based on a bridge circuit. When the resistances on the bridge arms satisfy the condition R1R3=R2R4, the bridge is balanced, and the output voltage is zero. When the resistance changes, the bridge becomes unbalanced, resulting in a voltage output. Strain gauges can be classified as single-arm, double-arm, or full-arm bridges, and their output voltage changes approximately linearly with the change in resistance. A strain gauge is a very thin sheet with two resistors made of resistance wire embedded on its upper surface and two identical resistors on its lower surface. These form a bridge circuit. When there is no pressure on the strain gauge, the output voltage is zero. When pressure is applied, the resistance on the upper side increases, and the resistance on the lower side decreases, causing the bridge to become unbalanced. Since the resistance wires are identical, the change in resistance is the same, and the output voltage is linearly related to the change in resistance. Thus, by calculating the pressure, the magnitude of the pressure can be measured. Besides piezoelectric sensors, there are also piezoresistive sensors made using the piezoresistive effect, strain gauge sensors that utilize the strain effect, and other different pressure sensors that utilize different effects and materials to perform their unique applications in different situations.
