Views: 1 Author: Site Editor Publish Time: 2022-06-13 Origin: Site
Capacitive tension Loacell
Capacitive tension loadcell is a tension loadcell that uses capacitance as a sensitive element to convert the measured tension into a change in capacitance value. This kind of tension loadcell generally uses a circular metal film or a metal-plated film as an electrode of the capacitor. When the film is deformed by tension, 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 tension loadcells belong to the polar distance variable capacitive sensors, which can be divided into single capacitive tension loadcells and differential capacitive tension loadcells.
The single capacitive tension loadcell consists of a circular membrane and a fixed electrode. The membrane deforms under tension, thereby changing the capacitance of the capacitor, and its sensitivity is roughly proportional to the area and tension of the membrane and inversely proportional to the membrane tension and the distance from the membrane to the fixed electrode. Another type of fixed electrode takes the shape of a concave spherical surface, and the diaphragm is a tension plane fixed around the periphery. This type is suitable for measuring low tension and has a high overload capacity. A single-capacitive tension loadcell for measuring high tension can also be made of a diaphragm with a piston moving pole. This type can reduce the direct tension area of the diaphragm, so that a thinner diaphragm can be used to improve the sensitivity. It is also integrally packaged with various compensation and protection sections and amplifier circuits to improve anti-jamming capability. This sensor is suitable for measuring dynamic high tension and for telemetry of aircraft. There are also types of single capacitive tension loadcells such as microphone type (ie microphone type) and stethoscope type.
The tension-receiving diaphragm electrode of the differential capacitive tension loadcell is located between two fixed electrodes, forming two capacitors. Under the action of tension, the capacity of one capacitor increases and the other decreases accordingly, and the measurement result is output by the differential circuit. Its fixed electrode is made of metallized layer on the concave curved glass surface. The diaphragm is protected against rupture by the concave surface when overloaded. Differential capacitive tension loadcell has higher sensitivity and better linearity than single capacitive tension loadcell, 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 tension loadcell
Piezoelectric tension loadcell is mainly based on the piezoelectric effect (Piezoelectric effect), which uses electrical components and other machinery to convert the tension to be measured into electricity, and then performs related measurement work. Precision instruments, such as many tension transmitters and tension loadcells.
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.
When the stress changes, the change in the electric field is very small, and some other piezoelectric crystals will replace the quartz. Potassium sodium tartrate has a large piezoelectric coefficient and piezoelectric sensitivity, but it can only be used in places where the indoor humidity and temperature are relatively low. Dihydrogen phosphate is an artificial crystal, it can be used in high humidity and high temperature environment, so its application is very wide. With the development of technology, the piezoelectric effect has also been applied to polycrystals. For example: piezoelectric ceramics, magnesium niobate piezoelectric ceramics, niobate piezoelectric ceramics and barium titanate piezoelectric ceramics, etc. are included.
The piezoelectric effect can be divided into: positive piezoelectric effect and inverse piezoelectric effect.
The positive piezoelectric effect means that when the crystal is subjected to an external force in a certain direction, electric polarization is generated inside, and charges of opposite signs are generated on two surfaces at the same time; when the external force is removed, the crystal returns to an uncharged state. state; when the direction of the external force changes, the polarity of the charge also changes; the amount of charge generated by the force on the crystal is proportional to the magnitude of the external force. Piezoelectric sensors are mostly made using the positive piezoelectric effect.
The inverse piezoelectric effect refers to the phenomenon of applying an alternating electric field to the crystal to cause mechanical deformation of the crystal, also known as the electrostrictive effect. Transmitters made with the inverse piezoelectric effect can be used in electroacoustic and ultrasonic engineering. There are five basic forms of stress deformation of piezoelectric sensitive elements: thickness deformation, length deformation, volume deformation, thickness shear, and plane shear. Piezoelectric crystals are anisotropic, and not all crystals can produce piezoelectric effects in these five states. For example, quartz crystal has no volume deformation piezoelectric effect, but has good thickness deformation and length deformation piezoelectric effect.