What are the Types of Pressure Sensors?
Devices that can measure pressure and provide remote electrical signals are collectively referred to as pressure sensors. The pressure sensor is an important part of the pressure detection instrument, and its structure is varied, the common types are strain type, piezoresistive type, capacitive type, piezoelectric type, vibration frequency pressure transducer and so on. In addition, there are photoelectric, optical fiber, ultrasonic pressure sensors and so on. The pressure transducer can directly convert the measured pressure into various forms of electrical signals, which is convenient to meet the requirements of centralized detection and control of the automation system, so it is widely used in industrial production.
Today we will talk about 5 types of pressure sensors.
Strain-type pressure sensor
A strain gauge pressure sensor is a sensor that indirectly measures pressure by measuring the strain of various elastic elements. According to the different materials, strain elements can be divided into two categories: metals and semiconductors. The working principle of strain elements is based on the "strain effect" of conductors and semiconductors, that is, when the conductor and semiconductor materials undergo mechanical deformation, their resistance value will change.
When the wire is subjected to external force, its length and cross-sectional area will change, and its resistance value will change. If the wire is stretched by external force, its length will increase, while the cross-sectional area will decrease, and the resistance value will increase. When the wire is compressed by external force, the length decreases and the cross-section increases, and the resistance value decreases. As long as the change in the voltage applied across the resistance is measured, the strain of the strained wire can be obtained.
Piezoresistive pressure sensor
Piezoresistive pressure sensor refers to a sensor made by using the piezoresistive effect of single crystal silicon material and integrated circuit technology. After the single crystal silicon material is subjected to the force, the resistivity changes, and the electrical signal output proportional to the force change can be obtained through the measurement circuit. It is also known as a diffused silicon piezoresistive pressure sensor. It is different from the adhesive strain gauge, which needs to indirectly feel the external force through the elastic sensitive element, but directly feels the measured pressure through the silicon diaphragm.
Piezoresistive pressure sensors are mainly based on the piezoresistive effect. The piezoresistive effect is used to describe the change in resistance of a material under mechanical stress. Unlike the piezoelectric effect, the piezoresistive effect only produces impedance changes, and does not produce electrical charges.
Capacitive pressure sensor
Capacitive pressure sensor is a pressure sensor that uses capacitance as a sensitive element to convert the measured pressure into a change in capacitance value. This kind of pressure transducer generally uses a circular metal film or a metal-plated film as an electrode of the capacitor. When the film is deformed by pressure, the capacitance formed between the film and the fixed electrode changes, and the output and voltage can be output through the measuring circuit. A certain relationship of electrical signals. Capacitive pressure sensors belong to the polar distance variable capacitive sensors, which can be divided into single capacitive pressure sensors and differential capacitive pressure sensors.
The single capacitive pressure sensor consists of a circular membrane and a fixed electrode. The membrane is deformed under the action of pressure, thereby changing the capacity of the capacitor. Its sensitivity is roughly proportional to the area and pressure of the membrane and inversely proportional to the tension of the membrane and the distance from the membrane to the fixed electrode. The single-capacitor pressure sensor also has a microphone type ( That is, the short type) and the stethoscope type.
The pressure-receiving diaphragm electrode of the differential capacitive pressure sensor is located between two fixed electrodes, forming two capacitors. Under the action of pressure, the capacity of one capacitor increases while the other decreases accordingly, and the measurement result is output by the differential circuit. Differential capacitive pressure sensor has higher sensitivity and better linearity than single capacitive pressure sensor, but it is more difficult to process (especially difficult to ensure symmetry), and it cannot achieve isolation of the gas or liquid to be measured, so it is not suitable for working in corrosive environments. sex or impurities in the fluid.
Piezoelectric pressure sensor
Piezoelectric pressure sensor is mainly based on the piezoelectric effect (Piezoelectric effect), which uses electrical components and other machinery to convert the pressure to be measured into electricity, and then performs related measurement work. Precision instruments, such as many pressure transmitters and pressure sensors.
Piezoelectric sensors cannot be used in static measurement, because the charge after being subjected to external force can only be preserved when the loop has an infinite input impedance. But that's not actually the case. Therefore, piezoelectric sensors can only be used in dynamic measurements. Its main piezoelectric materials are: ammonium dihydrogen phosphate, potassium sodium tartrate and quartz. The piezoelectric effect is found in quartz.
Inductive pressure sensor
Electromagnetic pressure sensor is a general term for a variety of sensors that utilize electromagnetic principles, including inductive pressure sensors, Hall pressure sensors, and eddy current pressure sensors.
The working principle of the inductive pressure sensor is that due to the different magnetic materials and permeability, when the pressure acts on the diaphragm, the size of the air gap changes, and the change of the air gap affects the change of the coil inductance. The processing circuit can convert the change of this inductance. into the corresponding signal output, so as to achieve the purpose of measuring pressure. This kind of pressure transducer can be divided into two types according to the change of magnetic circuit: variable reluctance and variable permeability. The advantages of inductive pressure sensors are high sensitivity and large measurement range; the disadvantage is that they cannot be used in high-frequency dynamic environments.
The main components of the variable reluctance pressure sensor are the iron core and the diaphragm. The air gap between them forms a magnetic circuit. When there is pressure, the size of the air gap changes, that is, the reluctance changes. If a certain voltage is applied to the iron core coil, the current will change with the change of the air gap, thereby measuring the pressure.