A displacement sensor, also known as a linear sensor, is a linear device that belongs to metal sensing. The function of the sensor is to convert various measured physical quantities into electrical quantities. In the production process, displacement measurement is generally divided into two types: measuring physical dimensions and mechanical displacement. According to the different forms of transformation of the measured variable, displacement sensors can be divided into analog and digital types. Simulations can be divided into two types: physical and structural.
1. According to the mode of exercise
Linear displacement sensorThe function of a linear displacement sensor is to convert the linear mechanical displacement into an electrical signal. To achieve this effect, the variable resistance slide rail is usually fixed at the fixed part of the sensor, and different resistance values are measured by the displacement of the slide plate on the slide rail. The sensor rail is connected to a steady-state DC voltage, allowing a small current of microamperes to flow. The voltage between the slider and the starting end is proportional to the length of the slider movement. Using a sensor as a voltage divider can minimize the requirement for the accuracy of the total resistance value of the slide rail, as changes in resistance caused by temperature changes will not affect the measurement results.
Angle displacement sensorAngle displacement sensor application for obstacle handling: Using an angle sensor to control your wheels can indirectly detect obstacles. The principle is very simple: if the motor angle sensor structure operates and the gear does not rotate, it indicates that your machine has been blocked by obstacles. This technology is very simple to use and very effective; The only requirement is that the moving wheels cannot slip on the floor (or slip too many times), otherwise you will not be able to detect obstacles. An idle gear connected to the motor can avoid this problem. This wheel is not driven by the motor but is driven by the movement of the device: if the idler wheel stops during the rotation of the drive wheel, it indicates that you have encountered an obstacle.
2. Based on material
Potentiometer type displacement sensor: It converts mechanical displacement into a resistance or voltage output that is linearly or arbitrarily related to it through potentiometer components. Both ordinary linear potentiometers and circular potentiometers can be used as linear displacement and angular displacement sensors, respectively. However, potentiometers designed for measuring displacement require a definite relationship between displacement changes and resistance changes. The movable brush of the potentiometer type displacement sensor in Figure 1 is connected to the measured object. The displacement of an object causes a change in the resistance of the moving end of the potentiometer. The change in resistance reflects the magnitude of displacement, while an increase or decrease in resistance indicates the direction of displacement. Usually, a power supply voltage is applied to the potentiometer to convert resistance changes into voltage output. The output characteristics of wire wound potentiometers also exhibit a stepped shape due to the change in resistance as the brush moves, taking the turn resistance as a step. If this type of displacement sensor is used as a displacement feedback component in a servo system, excessive step voltage will cause system oscillation. Therefore, in the production of potentiometers, the resistance value per turn should be minimized as much as possible. Another major drawback of potentiometer type sensors is their susceptibility to wear and tear. Its advantages are: simple structure, large output signal, convenient use, and low price.
Hall type displacement sensor: Its measurement principle is to maintain the excitation current of the Hall element (see semiconductor magnetic sensing element) unchanged and move it in a gradient uniform magnetic field. The displacement moved is proportional to the output Hall potential. The larger the magnetic field gradient, the higher the sensitivity; The more uniform the gradient change, the closer the relationship between Hall potential and displacement is to linearity. Figure 2 shows three types of magnetic systems that generate gradient magnetic fields: system a has a narrow linear range, and when displacement Z=0, the Hall potential≠ 0 B system when Z< Good linearity at 2mm, Hall potential at Z=0; The C system has high sensitivity and a measurement range of less than 1 millimeter. N and S in the figure represent positive and negative magnetic poles, respectively. Hall type displacement sensors have small inertia, high frequency response, reliable operation, and long service life, so they are commonly used in situations where various non electrical quantities are converted into displacement before measurement.
Photoelectric displacement sensor: It measures the displacement or geometric size of the object based on the amount of light flux obstructed by the object being measured. The characteristic is that it belongs to non-contact measurement and can be continuously measured. Photoelectric displacement sensors are commonly used for continuous measurement of wire diameter or as edge position sensors in strip edge position control systems.
3. Based on model characteristics
Conductive plastic displacement sensor: A special process is used to cover the DAP (Dipropylene Phthalate) resistance slurry on the insulation body, heat and polymerize it to form a resistance film, or press the DAP resistance powder thermoplastic into the groove of the insulation matrix to form a solid body as the resistance body. The characteristics are: good smoothness, excellent resolution, good wear resistance, long service life, low dynamic noise, high reliability, and chemical corrosion resistance. Servo systems used for space devices, missiles, aircraft radar antennas, etc.
Wire wound displacement sensor: It is made by using copper wire or nickel chromium alloy wire as a resistor and winding it on an insulating framework. The characteristics of wire wound potentiometers are small contact resistance, high accuracy, and low temperature coefficient. However, their disadvantages are poor resolution, low resistance, and poor high-frequency characteristics. It is mainly used as voltage divider, rheostat, instrument middle note zero and working point, etc.
Metal glass uranium displacement sensor: Using screen printing method, metal glass uranium resistance slurry is coated on a ceramic substrate according to a certain pattern, and then sintered at high temperature. The characteristics are: wide resistance range, good heat resistance, strong overload capacity, good moisture resistance, wear resistance, etc. It is a promising potentiometer variety, but the disadvantage is high contact resistance and current noise.
Metal film displacement sensor: The resistance body of a metal film potentiometer can be composed of alloy film, metal oxide film, metal foil, etc. The characteristics are high resolution, high temperature resistance, low temperature coefficient, low dynamic noise, and good smoothness.
Magnetic sensitive displacement sensor: eliminates mechanical contact, has a long lifespan and high reliability, but has disadvantages such as high requirements for the working environment.
Photoelectric displacement sensor: eliminates mechanical contact, has a long lifespan and high reliability, but has disadvantages such as digital signal output and cumbersome processing.
Magnetostrictive displacement sensor: Magnetostrictive displacement (liquid level) sensor, which accurately detects the absolute position of the active magnetic ring through internal non-contact measurement and control technology to measure the actual displacement value of the detected product; The high accuracy and reliability of this sensor have been widely applied in thousands of practical cases. Due to the fact that there is no direct contact between the active magnetic ring and the sensitive component used to determine the position, the sensor can be applied in extremely harsh industrial environments and is not susceptible to oil stains, solutions, dust, or other pollution. In addition, the sensor uses high-tech materials and advanced electronic processing technology, making it suitable for applications in high temperature, high pressure, and high oscillation environments. The output signal of the sensor is an absolute displacement value, and even if the power supply is interrupted or reconnected, data will not be lost, let alone reset to zero. Due to the non-contact nature of sensitive components, even continuous repeated testing will not cause any wear on the sensor, which can greatly improve the reliability and service life of the detection.
The magnetostrictive displacement (liquid level) sensor utilizes the principle of magnetostriction to accurately measure position by generating a strain pulse signal through the intersection of two different magnetic fields. The measuring element is a waveguide tube, and the sensitive components inside the waveguide tube are made of special magnetostrictive materials. The measurement process is generated by a current pulse in the electronic chamber of the sensor, which is transmitted inside the waveguide tube, thereby generating a circular magnetic field outside the waveguide tube. When the magnetic field intersects with the magnetic field generated by the movable magnetic ring as a position change on the waveguide tube, due to the effect of magnetostriction, a strain mechanical wave pulse signal is generated inside the waveguide tube, which is transmitted at a fixed sound speed, And it was quickly detected by the electronic room. Due to the fact that the transmission time of this strain mechanical wave pulse signal within the waveguide is directly proportional to the distance between the active magnetic ring and the electronic chamber, this distance can be highly accurately determined by measuring the time. Due to the fact that the output signal is a true absolute value rather than a proportional or amplified signal, there is no signal drift or variation, and there is no need for periodic rescaling.
Digital laser displacement sensor: Laser displacement sensors can accurately non-contact measure the position, displacement, and other changes of the measured object, mainly used for measuring geometric quantities such as displacement, thickness, vibration, distance, diameter, etc. of the detected object. According to the measurement principle, the laser displacement sensor principle is divided into laser triangulation measurement method and laser echo analysis method. Laser triangulation measurement method is generally suitable for high-precision and short distance measurement, while laser echo analysis method is used for long-distance measurement.
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