Principles of Common Optical Sensors Explained in Depth

There are many applications of optics, and sensors are often used in our daily lives. Today, we bring you a detailed explanation of the principles of optical sensors, filled with valuable information. Please save it!

Grating Sensors

Grating sensors refer to sensors that measure displacement using the principle of grating interference.

A grating is an optical device made up of numerous parallel slits of equal width and spacing. The commonly used gratings are made by engraving numerous parallel grooves on a glass plate, where the grooves are opaque and the smooth portions between the grooves allow light to pass through, effectively forming a slit. A finely crafted grating can have thousands or even tens of thousands of grooves within a width of 1 cm.

This type of grating that utilizes transmitted light diffraction is called a transmission grating, while those that utilize reflected light diffraction between two grooves are called reflection gratings. For example, if many parallel grooves are engraved on a surface coated with a metal layer, the smooth metal surface between the grooves can reflect light, forming a reflection grating. The interference pattern formed by the grating has optical amplification effects and error averaging effects, thus improving measurement accuracy.

Grating sensors consist of four parts: a scale grating, an indicator grating, an optical path system, and a measurement system.When the scale grating moves relative to the indicator grating, it forms an interference pattern of alternating bright and dark fringes that are approximately distributed according to a sine function.

These fringes move at the relative speed of the grating and are directly projected onto a photoelectric element, producing a series of electrical pulses at their output terminal. These pulses are then amplified, shaped, directed, and counted to produce a digital signal output that directly displays the measured displacement.

Structure and Working Principle of Grating Sensors:

The structure of a grating sensor consists of several key components: a light source, a main grating, an indicator grating, an aperture, and a photoelectric element.

1. Light Source:A tungsten bulb, which has a low power, exhibits low conversion efficiency and a short lifespan when used in combination with photoelectric elements. Semiconductor light-emitting devices, such as gallium arsenide light-emitting diodes, can operate within a range, with a peak emission wavelength close to that of silicon phototransistors, thus providing high conversion efficiency and fast response speed.

2. Grating:Composed of a main grating and an indicator grating with equal grating spacing. The main grating and the indicator grating overlap but do not completely coincide. The lines of both gratings are staggered at a small angle to obtain Moiré fringes. Generally, the main grating is movable, and it can move independently or along with the object being measured, with its length determined by the measurement range. The indicator grating is fixed relative to the photoelectric element.

3. Aperture:The aperture is the pathway for light between the light source and the receiving element, generally in a strip shape, with its length determined by the arrangement of the receiving elements and its width determined by the size of the receiving elements. It is adhered to the indicator grating plate.

4. Receiving Element:The receiving element is used to sense the movement of the Moiré fringes produced by the movement of the main grating, thereby measuring the displacement. When selecting the photo-sensitive element, factors such as sensitivity, response time, spectral characteristics, stability, and size should be considered.

Place the main grating overlapping with the scale grating, maintaining a small gap between them, and ensure that there is a small angle θ between the lines of both gratings, as shown in the figure below.

When a light source is illuminated, due to the light-blocking effect (for gratings with a line density ≤50 lines/mm) or the diffraction of light (for gratings with a line density ≥100 lines/mm), alternating bright and dark fringes are formed in a direction approximately perpendicular to the grating lines.

At the point where the lines of the two gratings coincide, light passes through the gap, forming bright bands; at the points where the lines of the two gratings are offset, dark bands are formed; these alternating bright and dark fringes are known as Moiré fringes.

The spacing of the Moiré fringes is related to the grating spacing W and the angle θ (in radians) between the lines of the two gratings:

(K is called the magnification factor).

When the indicator grating is stationary, and the lines of the main grating maintain a constant angle θ with the lines of the indicator grating while the main grating moves in the direction perpendicular to the lines, the Moiré fringes will move in the direction of the grating lines; if the grating moves in the opposite direction, the Moiré fringes will move in the opposite direction as well.

For every movement of the main grating by one grating spacing W, the Moiré fringes will also move by one spacing S accordingly. Therefore, by measuring the movement of the Moiré fringes, the amount and direction of grating movement can be easily measured, which is much easier than directly measuring the grating.

When the main grating moves one grating spacing W in a direction perpendicular to the grating lines, the Moiré fringes move by one fringe spacing. When the angle θ between the lines of the two gratings is small, it can be seen from the above formula that for a constant W, the smaller θ is, the larger B becomes, effectively magnifying the grating spacing W by a factor of 1/θ. Therefore, the magnification of the Moiré fringes is quite large, allowing for highly sensitive displacement measurement.

Moiré fringes are formed by many lines of the grating, exhibiting an averaging effect on line errors, which can largely eliminate the influence of local and short-period errors caused by line errors, achieving a measurement precision higher than that of the grating itself. Therefore, metrology gratings are particularly suitable for small displacement and high precision displacement measurements.

Characteristics of Grating Sensors

1. High precision.

Grating sensors are only slightly less accurate than laser interferometers for large range measurements of length or linear displacement. In terms of continuous measurement of circular division and angular displacement, grating sensors are among the most precise;

2. Large range measurement with high resolution.

Inductive synchronizers and magnetic grating sensors also have the characteristic of large range measurement, but their resolution and precision are not as good as grating sensors;

3. Capable of dynamic measurement, facilitating automation of measurement and data processing;

4. Strong anti-interference capability, with less stringent environmental requirements compared to laser interferometers, but not as adaptable as inductive synchronizers and magnetic grating sensors. Oil and dust can affect its reliability. It is mainly suitable for use in laboratories and well-conditioned workshops.

Types of Grating Sensors:

Gratings are mainly divided into two categories: one is Bragg gratings (also known as reflection or short-period gratings); the other is transmission gratings (also known as long-period gratings).

Fiber gratings can be structurally divided into periodic and non-periodic structures, and functionally divided into filtering gratings and dispersion compensating gratings. Dispersion compensating gratings are non-periodic gratings, also known as chirped gratings.

Fiber Bragg Grating Sensors

Fiber gratings are made using the photosensitivity within the fiber. The so-called photosensitivity in the fiber refers to the periodic change in refractive index along the fiber core produced when laser light is transmitted through doped fiber, forming a permanent spatial phase. The refractive index of the fiber grating will change according to the spatial distribution of light intensity. The spatial phase grating formed within the fiber core essentially acts as a narrowband (transmission or reflection) filter or mirror.

When a beam of broad-spectrum light passes through a fiber grating, the wavelengths that satisfy the Bragg condition of the fiber grating will be reflected, while the remaining wavelengths will continue to transmit through the fiber grating. This characteristic can be used to manufacture many unique fiber devices.

Chirped Fiber Grating Sensors:

Similarly to the working principle of fiber Bragg grating sensors, under the influence of external physical quantities, chirped fiber gratings will cause both a change in △λB and a broadening of the spectrum.

This type of sensor is very useful in situations where strain and temperature coexist. The chirped fiber grating will experience broadening of the reflected signal and displacement of the peak wavelength due to strain, while temperature changes will only affect the position of the centroid due to the temperature dependence of the refractive index (dn/dT). By simultaneously measuring the spectral displacement and broadening, both strain and temperature can be measured.

Long Period Fiber Grating Sensors:

Long period fiber gratings (LPG) are generally considered to have a period of several hundred micrometers. LPG couples light from the core into the cladding at specific wavelengths: λi= (n0 – ni clad)Λ. In this formula, n0 is the refractive index of the core, and ni clad is the effective refractive index of the i-th order axisymmetric cladding mode. Light in the cladding will rapidly attenuate due to losses at the cladding/air interface, leaving a series of loss bands.

A standalone LPG can have many resonances over a wide wavelength range, and the center wavelength of LPG resonance mainly depends on the refractive index difference between the core and cladding. Any changes caused by strain, temperature, or external refractive index variations will produce significant wavelength shifts in the resonance. By detecting △λi, information about changes in external physical quantities can be obtained. The responses of LPG resonances at a given wavelength typically have different amplitudes, making LPG suitable for multi-parameter sensing.

Infrared Sensors

Infrared technology has developed to a point where it is well-known and has been widely applied in modern technology, national defense, and industrial and agricultural fields. An infrared sensing system is a measurement system that uses infrared rays as the medium, which can be divided into five categories according to their functions:

(1) Radiometers, used for radiation and spectral measurements;

(2) Search and tracking systems, used for searching and tracking infrared targets, determining their spatial positions, and tracking their movements;

(3) Thermal imaging systems, which can produce images of the distribution of infrared radiation from the entire target;

(4) Infrared ranging and communication systems;

(5) Hybrid systems, which refer to combinations of two or more of the above systems.

First, let’s understand infrared light.

Infrared light is a part of the solar spectrum, and its most notable characteristic is its photothermal effect, radiating heat. It is the region of the spectrum with the greatest photothermal effect.Infrared light is invisible and, like all electromagnetic waves, possesses properties such as reflection, refraction, scattering, interference, and absorption. The speed of infrared light in a vacuum is 3×10^8 m/s. When propagating in a medium, infrared light will experience attenuation; it attenuates significantly in metals but can penetrate most semiconductors and some plastics. Most liquids absorb infrared radiation significantly.

Different gases absorb infrared light to varying degrees, and the atmosphere has different absorption bands for different wavelengths of infrared light.Research and analysis have shown that infrared light in the wavelength range of 1–5 μm and 8–14 μm has relatively high “transparency”. This means that infrared light at these wavelengths can penetrate the atmosphere better.

Any object in nature that has a temperature above absolute zero will emit infrared radiation.The photothermal effect of infrared light varies among different objects, with different intensities of thermal energy.

For example, a black body (an object that absorbs all infrared radiation incident on its surface), a mirror (an object that reflects all infrared radiation), a transparent body (an object that allows infrared radiation to pass through), and a gray body (an object that partially reflects or absorbs infrared radiation) will exhibit different photothermal effects. Strictly speaking, there are no true black bodies, mirrors, or transparent bodies in nature; most objects are gray bodies.

The above characteristics provide a significant theoretical basis for applying infrared radiation technology to satellite remote sensing, infrared tracking, and other military and scientific research projects.

Basic Laws of Infrared Radiation:

(1) Kirchhoff’s Law:At a certain temperature, the ratio of the radiation flux W per unit area of an object to its absorptivity is a constant for any object and is equal to the radiation flux W of a black body at that temperature per unit area. At a given temperature, the emissivity of an object = absorptivity (in the same band); the higher the absorptivity, the higher the emissivity.

The thermal radiation intensity of an object is proportional to the fourth power of its temperature, so even a slight temperature difference in an object can cause a significant change in infrared radiation energy. This characteristic forms the theoretical basis for infrared remote sensing.

(2) Stefan-Boltzmann’s Law:The total radiation flux of a black body increases rapidly with temperature, being proportional to the fourth power of the temperature. Therefore, even a small change in temperature can cause a significant change in radiation flux density. This is the theoretical basis for infrared devices to measure temperature.

(3) Wien’s Displacement Law:As temperature increases, the peak wavelength corresponding to the maximum radiation value shifts towards the short-wave direction.

The working principle of infrared sensors is not complex. A typical sensor system consists of the following parts:

(1) Measured Target.Infrared systems can be set based on the infrared radiation characteristics of the target to be measured.

(2) Atmospheric Attenuation.The infrared radiation emitted by the target will be attenuated as it passes through the Earth’s atmosphere due to scattering and absorption by gas molecules and various aerosols.

(3) Optical Receiver.It receives part of the infrared radiation from the target and transmits it to the infrared sensor, functioning similarly to a radar antenna, typically using a lens.

(4) Radiation Modulator.This modulates the radiation from the target into variable radiation light, providing target position information and filtering out large-area interference signals. It is also known as a modulation disk or chopper and has various structures.

(5) Infrared Detector.This is the core of the infrared system. It detects infrared radiation based on the physical effects that occur when infrared radiation interacts with matter, most commonly utilizing the electrical effects that arise from this interaction. Such detectors can be divided into photon detectors and thermal detectors.

(6) Detector Cooler.Some detectors must operate at low temperatures; therefore, the corresponding system must have cooling equipment. Cooling shortens response time and improves detection sensitivity.

(7) Signal Processing System.This amplifies and filters the detected signals and extracts information from them. This information is then converted into the required format and finally delivered to control devices or displays.

Following the above process, the infrared system can complete the measurement of the corresponding physical quantities. The core of the infrared system is the infrared detector, which can be divided into thermal detectors and photon detectors based on different detection mechanisms.

Thermal detectors absorb all incident radiation energy of various wavelengths; they are non-selective infrared sensors.Common photon detection effects include the photoelectric effect, the photoconductive effect (photovoltaic effect, photoconductive effect), and the photoelectromagnetic effect.

Thermal detectors utilize the radiative heat effect; when the detecting element receives radiation energy, its temperature increases, causing changes in temperature-dependent properties of the detector. By detecting changes in one of these properties, radiation can be detected. Most commonly, this is done by measuring changes in electrical quantities resulting from non-electrical physical changes when the element receives radiation. The response time of thermal detectors to infrared radiation is significantly longer than that of photonic detectors. The former typically has a response time of over ms, while the latter operates in the ns range. Thermal detectors do not require cooling, while most photon detectors do.

Main Technical Parameters of Infrared Detectors:

(1) Responsivity:

The responsivity of an infrared detector is the ratio of its output voltage to the input infrared radiation power.

In this formula, r — responsivity (V/W); U0 — output voltage (V); P — infrared radiation power (W).

(2) Response Wavelength Range:

The responsivity of infrared detectors is related to the wavelength of the incident radiation. As shown in the right figure, curve ① represents the characteristics of thermal detectors. The responsivity of thermal infrared detectors is independent of wavelength. The spectral response of photonic detectors is shown in curve ②.

λP corresponds to the responsivity peak rP, and rP/2 corresponds to the cutoff wavelength λc.

(3) Noise Equivalent Power (NEP):

Noise equivalent power, also known as minimum detectable power, is the incident signal power required to make the output signal of the detector equal to the noise voltage or current. It is a performance parameter that measures the ability of a photonic detector to receive weak signals. The power that produces a signal in the detector equals the detector’s own noise, thus representing the minimum target radiation that the detector can perceive. A smaller NEP indicates better detector performance. If the signal radiation power is less than the noise equivalent power, the detector’s output signal will be less than the noise. This means that the detector will be unable to perceive target radiation. Therefore, the noise equivalent power essentially represents the minimum target radiation that the detector can detect, indicating the sensitivity of a detector. Smaller NEP means higher sensitivity. NEP is related to the corresponding spectral segment of the detector, modulation frequency, operating temperature, bias, sensitive area, and acceptance angle.

Pyroelectric Infrared Sensors

With the development of society, various automatic control systems that facilitate life have begun to enter people’s lives, one of which is the automatic door system based on pyroelectric infrared sensors.

Pyroelectric infrared sensors are thermal-type infrared sensors based on the principle of the pyroelectric effect.The internal pyroelectric element is composed of high pyroelectric coefficient materials like lead titanate ceramic and lithium tantalate, combined with optical filter windows. Its polarization changes with temperature. The pyroelectric infrared sensor consists of a sensing element, an interference filter, and a field-effect transistor (FET) matcher. During design, high pyroelectric materials are made into thin sheets of a certain thickness, and metallic electrodes are deposited on both sides, followed by polarization to create the pyroelectric sensing element.

Principle of Pyroelectric Infrared Sensors:

1. Characteristics of Pyroelectric Infrared Sensors:

Pyroelectric infrared sensors and thermocouples are both thermal-type infrared sensors based on the principle of the pyroelectric effect. The difference is that the pyroelectric infrared sensor has a much higher pyroelectric coefficient than thermocouples. Its internal pyroelectric element is composed of high pyroelectric coefficient materials like lead titanate ceramic and lithium tantalate, combined with optical filter windows. To suppress interference from self-temperature changes, this sensor is designed to connect two identical pyroelectric elements in reverse series or in a differential balance circuit, allowing it to detect changes in infrared energy emitted by objects non-contact and convert them into electrical signals. The introduction of FET in the structure of the pyroelectric infrared sensor serves to complete impedance transformation. Since the output of the pyroelectric element is a charge signal that cannot be used directly, it needs to be converted into a voltage form using a resistor with a high impedance of up to 10^4 MΩ. Therefore, the introduced N-channel junction FET should be connected in a common drain configuration, functioning as a source follower to achieve impedance transformation. The pyroelectric infrared sensor consists of a sensing element, an interference filter, and a field-effect transistor matcher. During design, high pyroelectric materials are made into thin sheets of a certain thickness, and metallic electrodes are deposited on both sides, followed by polarization to create the pyroelectric sensing element. Since the polarization voltage is polar, the polarized sensing element also has positive and negative polarities.

2. Working Principle and Characteristics of Passive Pyroelectric Infrared Sensors:

The human body has a constant temperature, generally around 37 degrees Celsius, and emits infrared radiation at a specific wavelength of around 10 μm. Passive infrared sensors work by detecting the infrared radiation emitted by the human body around 10 μm. The infrared radiation emitted by the human body is enhanced through a Fresnel filter and focused onto the infrared sensing element. The infrared sensing element typically uses a pyroelectric element, which loses its charge balance when it receives infrared radiation from the human body, releasing charge, and the subsequent circuit processes this to produce an alarm signal.

1) This sensor is designed to detect radiation from the human body, so the pyroelectric element must be very sensitive to infrared radiation around 10 μm.

2) To ensure sensitivity only to human infrared radiation, a special Fresnel filter is usually placed over its radiation surface to significantly control environmental interference.

3) In passive infrared sensors, the sensor contains two pyroelectric elements connected in series or parallel. The polarization directions of the two electrodes are opposite, meaning that the background radiation has nearly the same effect on both pyroelectric elements, causing their pyroelectric effects to cancel each other out, resulting in no output signal from the detector.

4) Once a person enters the detection area, the infrared radiation from the body is focused through a mirror and received by the pyroelectric element. However, the two pyroelectric elements receive different amounts of heat, resulting in different pyroelectric outputs that do not cancel out, triggering an alarm after signal processing.

5) The Fresnel filter has different focal lengths (detection distances) based on performance requirements, resulting in different monitoring fields; the more fields there are, the tighter the control.

3. Pyroelectric Effect:

When certain crystals are heated, equal but opposite charges will accumulate at both ends of the crystal. This polarization phenomenon caused by temperature changes is known as the pyroelectric effect. Generally, the bound charge generated by spontaneous polarization in the crystal is neutralized by free electrons from the air attaching to the surface of the crystal, preventing the spontaneous polarization dipole moment from manifesting. When temperature changes, the centers of positive and negative charges in the crystal structure shift relative to each other, causing a change in spontaneous polarization, leading to charge depletion on the crystal surface, which is proportional to the degree of polarization.

Materials that can produce the pyroelectric effect are called pyroelectric materials or pyroelectric elements, with common materials including single crystals (like LiTaO3), piezoelectric ceramics (like PZT), and polymer films (like PVFZ).

Based on the principle of Fresnel, infrared light is divided into visible and blind areas while also focusing, greatly increasing the sensitivity of the pyroelectric infrared sensor (PIR). Fresnel lenses come in refractive and reflective forms, serving to focus and refract (reflect) the thermal infrared signals onto the PIR; they also divide the detection area into several bright and dark zones, allowing moving objects entering the detection area to generate changes in thermal infrared signals in the form of temperature changes, thus enabling the PIR to produce varying electrical signals.

If we connect an appropriate resistor to the pyroelectric element, when the element is heated, current will flow through the resistor, yielding a voltage signal across its terminals.

Fiber Optic Gyroscope Sensors

Fiber optic gyroscopes are a new type of fiber rotation sensor that emerged with the rapid development of fiber optic technology.They are sensitive elements based on a coil of optical fiber, where light emitted from a laser diode travels in both directions along the optical fiber. The change in light propagation path determines the angular displacement of the sensitive element. Gyroscope sensors mainly consist of active components like light sources and detectors, as well as passive components like fiber couplers and phase modulators, along with the optical fiber itself.

Gyroscope sensors can be classified in various ways. Based on the working principle, they can be divided into interferometric, resonant, and stimulated Brillouin scattering fiber gyroscopes; based on the method of processing electrical signals, they can be divided into open-loop and closed-loop fiber gyroscopes; and based on structure, they can be divided into single-axis and multi-axis fiber gyroscopes.

Gyroscope sensors have advantages such as lightweight, compact size, low cost, high precision, and high reliability. These prominent features make them particularly ideal for applications in aerospace, airborne systems, and military technologies, thus attracting significant attention from users, especially the military. Research on gyroscope sensors, primarily led by the US, Japan, and France, has made substantial progress.

Most research on fiber gyroscopes focuses on interferometric types, with only a few companies still researching resonant fiber gyroscopes. The commercialization of gyroscope sensors began in the early 1990s, and medium to low precision fiber gyroscopes have already been commercialized and applied across multiple fields, while the development and research of high-precision fiber gyroscopes are progressing towards maturity.

In China, fiber gyroscopes have made significant strides through the efforts of relevant academic institutions and research institutes. Although the level of development is still somewhat behind international standards, they have met or approached medium and low precision requirements and have begun attempts at industrialization in recent years.

Laser Displacement Sensors

Laser displacement sensors utilize the high directionality, monochromaticity, and brightness of lasers to achieve non-contact long-distance measurements. Laser displacement sensors (magnetostrictive displacement sensors) are new measuring instruments made using these advantages of lasers, greatly improving the precision and reliability of displacement measurements and providing an effective method for non-contact displacement measurement.

Due to their high measurement precision and non-contact measurement characteristics, laser displacement sensors are widely used in universities and research institutions, the automotive industry, mechanical manufacturing, aerospace and military industries, and precision measurement and testing in metallurgy and materials industries.

Laser displacement sensors can accurately measure the position, displacement, and other changes of the measured object without contact, primarily applied in detecting displacements, thicknesses, vibrations, distances, diameters, and other geometric measurements.

According to the measurement principle, laser displacement sensors can be divided into laser triangulation measurement and laser echo analysis measurement. Laser triangulation measurement is generally suitable for high-precision, short-distance measurements, while laser echo analysis is used for long-distance measurements.

Below, we will introduce the two measurement principles of laser displacement sensors.

Measurement Principles of Laser Displacement Sensors

1. Laser Triangulation Measurement Principle

Figure 1: Diagram of Laser Triangulation Measurement Principle

A semiconductor laser 1 is focused onto the measured object 6 by lens 2. The reflected light is collected by lens 3 and projected onto a CCD array 4; the signal processor 5 calculates the distance to the object based on the position of the light spot on array 4 using trigonometric functions.

The laser emitter directs visible red laser light onto the surface of the object, and the reflected laser light is received by the internal CCD linear camera through the receiving lens. Depending on the distance, the CCD linear camera can “see” the light spot at different angles. Based on this angle, the distance between the laser and the camera can be determined, allowing the digital signal processor to calculate the distance between the sensor and the measured object.

Simultaneously, the position of the light beam on the receiving element is processed through analog and digital circuits, and analyzed by a microprocessor to calculate the corresponding output value, which is proportionally output as a standard data signal within the user-defined analog window. If a switch output is used, it will be turned on within the set window and turned off outside the window. Additionally, the analog and switch outputs can be set to independent detection windows.

2. Laser Echo Analysis Measurement Principle

Laser displacement sensors utilize the echo analysis principle to measure distances with a certain degree of precision. The internal structure of the sensor consists of processing units, echo processing units, laser emitters, and laser receivers. The laser displacement sensor emits one million pulses per second towards the detection object and receives them back at the receiver. The processor calculates the time required for the laser pulse to encounter the detection object and return to the receiver to determine the distance value, which is the average output of thousands of measurements.

Figure 2: Diagram of Laser Echo Analysis Measurement Principle

Laser Ranging Sensors

Laser ranging sensors first emit laser pulses aimed at the target using a laser diode. After reflecting off the target, the laser scatters in all directions. Some of the scattered light returns to the sensor receiver, where it is captured by the optical system and imaged onto an avalanche photodiode. The avalanche photodiode is an optical sensor that internally amplifies signals, allowing it to detect extremely weak light signals. By recording and processing the time taken from light pulse emission to reception, the distance to the target can be determined.

Laser sensors must accurately measure the transmission time, as the speed of light is very fast.

For example, the speed of light is approximately 3X10^8 m/s; to achieve a resolution of 1 mm, the ranging sensor’s electronic circuit must be able to discern the following very short time:

0.001m(3X10^8m/s)=3ps

Discerning 3 ps is a very high requirement for electronic technology, making it prohibitively expensive to achieve.

However, modern laser sensors cleverly circumvent this obstacle by using a simple statistical principle, namely the averaging method, to achieve a resolution of 1 mm while ensuring response speed.

During operation, a long-distance laser rangefinder emits a narrow laser beam towards the target. The photodetector receives the reflected laser beam, and a timer measures the time taken for the laser beam to travel from emission to reception, calculating the distance from the observer to the target. The LED white light speedometer images onto the integrated circuit chip CCD inside the instrument. The CCD chip has stable performance, a long working life, and is minimally affected by working environments and temperatures. Therefore, the measurement accuracy of the LED white light speedometer is guaranteed, and its performance is stable and reliable.

Source: Mechanical Engineering Collection