Displacement sensor

Displacement sensor

Linear displacement transducer, also known as the sensor, which is divided into inductive displacement sensor, capacitive displacement sensors, optical displacement sensor, displacement sensor ultrasonic displacement sensors, Hall-type displacement sensor. Inductive displacement sensor is a metal sensor is a linear device, powered on, the switch sensor surface will result in an alternating magnetic field, when the metal object close to the sensor surface, the metal in the vortex and absorb the energy of the oscillator, the oscillator output amplitude of linear attenuation, attenuation changes and then to complete the purpose of non-contact detection of objects.

Introduction

Inductive displacement sensor with no moving contacts from dust and other non-metallic work factors, and low power consumption, long life, can be used in a variety of harsh conditions. Displacement sensors are used in automated production line equipment, analog intelligent control.

Displacement and position of objects in motion on the amount of movement and displacement of the scope of measurement is quite extensive. Usually small displacement strain, inductive, differential transformer, eddy current, Hall sensors to detect the displacement of a large common inductosyn, grating, capacitive, magnetic and other sensor technology to measure the gate. Grating sensors which are easy to achieve because of digital, high accuracy (currently the highest resolution up to nano-scale), anti-interference ability, no one reading error, easy to install, use and reliable, in machining, instrumentation and other industries Been increasingly widely used.

Principle

Metrological grating is the use of grating moire fringe phenomenon to measure the displacement. "Moore" For the original French Moire, which means the water ripple. French silk workers found when the two layers of thin silk, stacked together, will have a ripple-like pattern hundreds of years ago; if the relative motion of thin silk, the pattern will move with it, this strange is the moire fringe pattern. Generally, as long as there is a certain cycle curve clusters overlap, they will produce Moire fringe. Grating in the practical application of measurement has two transmission gratings and reflection gratings; action principle can be classified according to their radiation grating and phase grating; according to their use can be divided

into linear and circular gratings. The following example to be discussed transmission grating. Transmission grating engraved on a uniform that is parallel to the gate line engraved line, a line width for the moment, b is fracture width between the two groove, W = a + b as grating pitch. Currently used carved 10,25,50,100,250 per mm grating strips lines. Moire fringe grating measured horizontal displacement, need two gratings. A grating as the main grating, its size is consistent with the measurement range; the other one is a very small, as instructed grating. To measure the displacement must be added in the main grating side of the light source, grating side of the instruction plus photoelectric receiving elements. When the primary grating and grating relative movement direction, the shading effect of leaving the grating Moiré fringe mobile, fixed grating in the direction side of the optical components, the light intensity changes into electrical signals. Since the limited size of the light source and diffraction grating effect, making the signal for the pulse signal.

Signal Processing

To the principles identified

In practice, the displacement has two directions, that is, choose a direction, the displacement of the positive and negative points, so with a determination of Moire fringe optoelectronic devices can not determine the direction of displacement. In order to distinguish the need to have π/ 2 phase difference of the two moiré fringe signals.

Subdivision

With the improvement of measurement accuracy, to pitch as a unit can not meet the requirements, the need to take appropriate measures to be broken down on the Moire fringe. Subdivision is the so-called changes in the moiré fringe of a cycle, issued a number of pulses to reduce the pulse equivalent. If given within a period of n pulses, the accuracy can improve n equipment, and each pulse is equivalent to the original pitch of 1 / n. After the count of the sub-pulse frequency increased n times, so also called n multiplier. There are two commonly used subdivision method: First, the direct segment. The difference between the 1 / 4 position on the Moire fringe spacing placed the two optical components, get the two 90 ° phase difference signal, the use of four inverter followed by a difference of RP after 90 ° of the AC signal. Similarly, in the two moire fringe order of distance between the place four 1 / 4 fringe spacing of the optoelectronic components, are available to the exchange of the four 90 ° phase difference signal, to achieve four interpolated. Second, the circuit is broken down.

ASIC

ASIC QA740210 quadrature phase and also has identified four segments of the function of frequency can be two orthogonal frequency square wave generated after four two-Luke, by counting the signal, can send even the clock reversible counter Add, subtract, count, can also be sent directly to micro-computer (including MCU) for data processing.

Features:

⑴, digital differential circuit: 4 Differential pulse width determined by the frequency of cycles, therefore, is consistent, and can be easily in a wide range of choices.

⑵, criticality alarm and over-speed warning two speed Tip: You can limit the grating velocity when approaching the critical alarm information is given to the operator speed control in a timely grating movement. Faster than the time limit in the circuit will give an error message.

⑶, absolutely zero control: absolute zero setting will bring much convenience operators, such as power failure after the re-positioning. This circuit has "absolutely zero to start counting"and"stop the count to the absolute zero"and"has nothing to do with the absolute zero" three modes.

⑷, Chip Select: This circuit has a chip select terminal, it can be multi-standard digital display system.

⑸, COMS process: input and output voltage and current with the 4000 series CMOS and LSTTL circuits compatible.

Categories

Classified according to the motion method

Linear displacement sensor

Principle:

Function of linear displacement sensor is the linear mechanical displacement into electrical signals. To this effect, usually slide-set variable resistor the fixed part of the sensor, through the slider on the rail to measure the displacement of different resistance. Steady-state DC voltage rails connecting the sensor to allow a small flow through the micro-ampere current, slip between the film and the beginning of the voltage terminal, and the length of vane movement. The sensor can be used as a divider rails to minimize the total resistance of the requirements of accuracy, because the resistance caused by the change of temperature change will not affect the measurement results.

LT linear displacement sensor:

⊙ widely used in injection molding, machine tool and machining industry

⊙ infinite resolution

⊙ Duration: 50 to 900mm

⊙ Independent Linearity: ± 0.05%

⊙ displacement speed: 5m / s, 10 m / s optional

⊙ Operating temperature: -30 to +100 ℃

⊙ a variety of electrical connections

⊙ Protection class: IP60 (IP65 optional)

Angular displacement sensor

According to classified material

Metal film sensors, conductive plastic sensors, photoelectric sensors, magnetic sensors, metal glass uranium sensor, the sensor winding.

Potentiometer displacement sensors which components will be through the potentiometer associated mechanical displacement into a linear or any function of the resistance or voltage output. General linear and circular potentiometer potentiometer can be used as a linear displacement, respectively, and the angular displacement sensor. However, to achieve the purpose of measuring the displacement potentiometer designed to require change and resistance change in the displacement of a definite relationship between. Potentiometer displacement sensors and the measured object can be linked to dynamic brush. Potentiometer caused the displacement of objects moving side of the resistance change. Reflect the change in resistance value of displacement, the increase or decrease the resistance that the displacement direction. Usually pass on the potentiometer to supply voltage to the resistance change is converted to voltage output. Wirewound potentiometer wiper is moved due to its resistance to change turn resistance ladder, the ladder-shaped output characteristic was also found .If this displacement sensor used in the servo system position feedback device, the excessive voltage can cause system oscillation step. Therefore, the production of the potentiometer should be to minimize the resistance of each turn. Potentiometer sensor is another major drawback is easy to wear. Its advantages are: simple structure, large output, convenient, low prices.

Hall displacement sensor measuring principle is to maintain its Hall component (see semiconductor magnetic components) of the excitation current constant, and make it in a uniform magnetic field gradient to move, then move the displacement is proportional to the output of the Hall Potential. The greater the magnetic field gradient, the higher the sensitivity; gradient more uniform, Hall electric potential and the closer relationship between the linear displacement. Hall of inertia displacement

sensors, high frequency response, reliable, long life, so commonly used in all kinds of non-electricity and then converted into the displacement measurement occasions.

Optical displacement sensor is based on the number of the measured object to block the flux measurement object displacement or geometry. Characterized by a non-contact measurement, and continuous measurements. Optical displacement sensor used in the continuous measurement of wire diameter or the edge of the strip edge position control system for position sensors.

Sensor market prospects

Consulting INTECHNOCONSULTING sensor market report, the global sensor market volume in 2008 was 50.6 billion U.S. dollars, the global sensor market in 2010 up to 600 billion USD. Survey shows that Eastern Europe, Asia Pacific and Canada become the fastest growing region sensor market, while the United States, Germany, Japan remains the largest regional distribution of the sensor market. On a global scale, the sensor market is still the fastest-growing auto market, accounting for the second is the process control market, promising telecommunications market prospects. Currently, the global sensor market is changing among the innovative trend of rapid growth presents. Experts point out that the main field of sensor technology will be based on the existing extension and increase, States will compete to accelerate next-generation sensor development and industrialization, it will become increasingly fierce competition. Development of new technologies will redefine the future of the sensor market, such as wireless sensors, fiber optic sensors, smart sensors and metal oxide sensors and the emergence of new sensors to expand market share.