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Ⅰ IntroductionThe Hall Effect is the most common method of measuring magnetic fields, and Hall Effect Sensors are widely used and have a wide range of applications in modern times. For example, they're used in cars as wheel speed sensors and crankshaft or camshaft position sensors. They're often used as switches, MEMS compasses, proximity sensors, and other applications. Now we'll take a look at a few of these sensors to see how they function, but first, let's define the Hall Effect. CatalogⅠ IntroductionⅡ What is Hall EffectⅢ What is a Hall Effect SensorⅣ How Does a Hall Effect Sensor WorkⅤ Hall Effect Sensor Types  5.1 Threshold  5.2 LinearⅥ Hall Effect Sensor Uses  6.1 Head-on Detection  6.2 Sideways DetectionⅦ Hall Effect Sensor Applications  7.1 Hall Effect Sensor in Rotary Applications  7.2 Hall Effect Sensor in Proximity Applications  7.3 Proximity Hall Effect Sensor Uses in RoboticsⅧ How to Test Hall Effect SensorsⅨ FAQ Ⅱ What is Hall EffectThe experiment that describes the Hall Effect is as follows: If we have a thin conductive plate like the one shown and apply current to it, the charge carriers will flow in a straight line from one side to the other.Now, if we apply a magnetic field near the plate, we can disrupt the charge carriers' straight flow due to a force known as the Lorentz Force. The electrons would deflect to one side of the plate, while the positive holes would deflect to the other. This means that if we now connect the other two sides with a meter, we can get a voltage that can be measured.As previously mentioned, the effect of obtaining a measurable voltage is known as the Hall Effect, after Edwin Hall, who discovered it in 1879.  Ⅲ What is a Hall Effect SensorA Hall Effect sensor detects changes in magnetic field power. This sensor opens up a wide range of possibilities for robotic sensor applications.They can be used in applications such as proximity, positioning, speed, and current sensing. They're usually used on pneumatic cylinders, where they're used to communicate the cylinder's position to a PLC or robotic controller.Automotive, personal electronics, and robotics are only a few of the industries that use Hall Effect sensors. Depending on the application, they have some advantages over other sensors. They are fully encased because they operate with a magnetic field, making them less vulnerable to damage from dirty or wet conditions. They are less likely than mechanical systems to wear out or skew readings after a large number of cycles. Hall Effect sensors are useful for a wide range of applications due to their reliability and longevity since they do not need physical contact to operate properly. They can provide more repeatability and accuracy than mechanical units because they do not physically interfere with the machinery or tooling.  Ⅳ How Does a Hall Effect Sensor WorkIt's best to start with the basics of the Hall Effect to comprehend a Hall Effect sensor. As current flows through a conductor in the presence of a magnetic field, the electrons are pushed to one side of the conductor by the magnetic field. The Hall Effect can be used to measure electric current in conductors that are built with certain parameters in view. The voltage across a flat metallic conductor, for example, reveals the Hall Effect much better than the voltage across around one.The electrons moving over the conductor are forced to one side when a magnetic field is applied to the flat plate. Since the sum of deflection can be calculated, the apparatus has a wide range of applications. A flat plate conductor is used to calculate magnetic strength in a Hall Effect sensor. When a magnet gets close to the sensor, the sensor detects it and sends the information to a controller. The charge across the plate is shifted to one side while the magnet is near the sensor, producing a positive charge on one side and a negative charge on the other. The voltage difference between the two sides of the plate is determined, and it can be used to calculate magnetic strength or sensor proximity.  Ⅴ Hall Effect Sensor TypesHall Effect Sensors come in two basic types:5.1 ThresholdWhen the field strength reaches a certain amplitude and/or polarity, the threshold (also known as digital or on-off) produces a constant hall voltage. There are several different threshold device configurations, such as latching devices that turn on when a positive field strength reaches the threshold but only turn off when a negative field of the same strength reaches the threshold, devices that turn on when only a positive field reaches the threshold but are off otherwise, and devices that turn on when either a positive or negative field reaches the threshold. Thresholds can also be programmed in some computers. 5.2 LinearLinear (analog output sensor) generated a hall voltage proportional to the magnetic field strength around it. The polarity of the voltage swing is determined by the direction of the surrounding magnetic field. When expressive movements must be sensed as small changes in position, linear devices are more commonly used in musical applications. Ⅵ Hall Effect Sensor UsesHall effect sensors are powered by a magnetic field, and in many applications, a single permanent magnet connected to a moving shaft or device may control the device. There are many different forms of magnet sensing motions, including "Head-on", "Sideways", "Push-pull", and "Push-push" among others. To ensure optimum sensitivity, magnetic lines of flux must always be perpendicular to the sensing region of the system and of the right polarity, regardless of the configuration. High field strength magnets with a significant change in field strength for the necessary movement are also required to ensure linearity. There are several ways to detect a magnetic field, and two of the most common sensing configurations using a single magnet are shown below: Head-on detection and sideways detection are two types of detection. 6.1 Head-on DetectionThe magnetic field must be perpendicular to the hall effect sensing system and approach the sensor straight on towards the active face for "head-on detection" as the name suggests. In a way, it's a "front-on" approach. This direct approach produces an output signal, VH, which in linear devices reflects the magnetic field power, or magnetic flux density, as a function of distance from the hall effect sensor. The output voltage increases as the magnetic field gets closer and hence stronger, and vice versa. Positive and negative magnetic fields can also be differentiated by linear instruments. For indicating positional detection, non-linear devices can be made to trigger the output "ON" at a pre-set air gap distance away from the magnet. 6.2 Sideways Detection"Sideways detection" is the second sensing configuration. This necessitates moving the magnet sideways across the face of the Hall effect element. For example, counting rotational magnets or measuring the speed of rotation of motors, sideways or slide-by detection is useful for detecting the presence of a magnetic field as it travels across the face of the Hall element within a fixed air gap distance. A linear output voltage representing both a positive and negative output can be generated depending on the direction of the magnetic field as it passes by the sensor's zero-field centerline. This enables the identification of directional movement in both vertical and horizontal directions. Hall Effect Sensors have a wide range of applications, especially as proximity sensors. Where the environmental factors include water, vibration, dirt, or oil, such as in automotive applications, they can be used instead of optical and light sensors. Present sensing can also be done with Hall effect instruments.A circular electromagnetic field is formed around a conductor when a current passes through it, as we learned in previous tutorials. Electrical currents ranging from a few milliamps to thousands of amperes can be calculated from the induced magnetic field by placing the Hall sensor next to the conductor without the use of large or expensive transformers and coils. Hall effect sensors can be used to detect ferromagnetic materials such as iron and steel, in addition to detecting the presence or absence of magnets and magnetic fields, by putting a small permanent "biasing" magnet behind the active region of the device. Any shift or disruption to this magnetic field caused by the introduction of a ferrous material can be detected with sensitivities as low as mV/G. Depending on the type of device, whether digital or linear, there are a variety of ways to connect Hall effect sensors to electrical and electronic circuits. The use of a Light Emitting Diode, as shown below, is a very simple and easy-to-build example. Hall effect sensors can be used in a variety of ways due to the different magnetic movements. In both industrial and domestic environments, the most common application for these instruments is to measure objects' presence, position, and proximity. Current sensors, pressure sensors, and fluid flow sensors are all popular applications for Hall effect sensors in industrial and manufacturing processes. In current transformers, Hall effect sensors are an inexpensive, contactless way to measure DC magnetic flux.  Ⅶ Hall Effect Sensor Applications7.1 Hall Effect Sensor in Rotary ApplicationsSpeed sensors operate by counting the number of times a shaft or disk rotates in a given amount of time. A disk attached to the motor shaft rotates next to the Hall Effect sensor and has magnets on its perimeter. The state of the sensor is shifted as the magnets move through it. Based on this data, the sensor calculates the revolutions. For example, if the disk or shaft has four magnets, the sensor can switch states four times per revolution.This enables the sensor to measure the RPM based on the known parameter that four pulses per revolution will occur. This technology is used in brushless DC motors to track speed and detect shaft position. This enables them to run at specific RPM ranges while still allowing them to change the motor speed at any time. This makes controlling the motors a lot easier. It also allows them to monitor the location of the shaft on the motor, making them much more flexible in the robotics industry than motors without Hall Effect sensors. 7.2 Hall Effect Sensor in Proximity ApplicationsBased on a magnetic field, Hall Effect sensors can detect proximity. If the magnetic field strength is constant and defined, the position of the sensor in relation to the magnet can be determined. When a magnet moves into its range, the sensor changes states and alerts the controller. Proximity Hall Effect sensors can be used in a variety of ways. Robotic tooling, robotic grippers, pneumatics, and a variety of other non-robotic applications use them.7.3 Proximity Hall Effect Sensor Uses in RoboticsProximity Hall effect sensors can also be used in robotics. They're good for detecting magnetic strength and magnet proximity. Hall Effect sensors may be used to meet a variety of safety requirements. They are often used in tooling to provide clamp confirmation to the controlling device. Clamp confirmation locks the cell's operation until all sections are fully clamped, allowing it to function safely. Magnets embedded in the tooling that fall within the sensing range of the Hall Effect sensor when properly clamped normally dictate part confirmation. The robotic controller or PLC knows the cell is safe to operate when all sensors display a signal. In the robotics industry, Hall Effect sensors are extremely useful. For sensing changes in the cell, most robotic cells use a Hall Effect sensor. They are used to read the speed and position of DC brushless motors. They are used in pneumatic cylinders to determine if the cylinder is extended or retracted. They can also be used to keep staff healthy by notifying the controlling body of tooling clamp confirmation. Without Hall Effect sensors, the robotics industry will be very different.  Ⅷ How to Test Hall Effect SensorsThe camshaft and crankshaft position sensors are Hall effect sensors that control the camshaft and crankshaft position, respectively. In front of the sensor, a small magnet passes. The output voltage increases as the magnet get closer to the sensor. The voltage drops as the magnet moves away from the sensor. To assess shaft position, the electronic control module tracks these sensor outputs. The ECM can maintain precise engine control thanks to the camshaft and crankshaft position sensors, as well as other electrical sensors, solenoids, and injectors. Understand the basics of Hall effect sensors will aid you in properly testing a questionable sensor. • Step 1Remove the sensor from the engine block. Remove any oil, dirt, or metal shavings from the sensor tip. • Step 2Examine the engine's schematic for the camshaft sensor or crankshaft signal to the ECM. The signal wire from the ECM should be removed. Connect the signal wire to one end of the jumper wire. Connect the jumper wire's other end to the optimistic probe's edge. Connect the negative probe to stable chassis ground. Connect the negative probe to the chassis ground with a jumper and alligator clips if necessary. To test DC volts, switch the electric voltmeter. Turn the key switch to "On". Ideally, the voltage should be about 0 volts. Slowly rotate the magnet perpendicular to the sensor's front. When the magnet approaches the sensor, the voltage should rise, and as it moves away, the voltage should fall. There is a problem with the sensor or the sensor's connections if the voltage does not change. Ⅸ FAQ1. How does a Hall effect sensor work?Using semiconductors (such as silicon), Hall effect sensors work by measuring the changing voltage when the device is placed in a magnetic field. In other words, once a Hall effect sensor detects that it is now in a magnetic field, it can sense the position of objects. 2. What triggers a Hall effect device?Hall effect sensors are activated by a magnetic field and in many applications, the device can be operated by a single permanent magnet attached to a moving shaft or device. There are many different types of magnet movements, such as ‘Head-on’, ‘Sideways’, ‘Push-pull’ or ‘Push-push’ etc sensing movements. 3. What is the use of a hall effect sensor?Hall effect sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. 4. What is the principle of the Hall effect?The Hall Effect principle states that when a current-carrying conductor or a semiconductor is introduced to a perpendicular magnetic field, a voltage can be measured at the right angle to the current path. 5. How sensitive is a Hall effect sensor?These ratiometric devices have a sensitivity of 5 mV/gauss and 2.5 mV/ gauss, respectively, an operating temperature range of -40°C to +150°C, and are temperature compensated over their full operating range. 6. What is the difference between a Hall effect sensor and an inductive sensor?Inductive sensors detect metallic objects and hall effect sensors detect the presence of a magnetic field. 7. What is the origin of the Hall effect?The history of the Hall effect begins in 1879 when Edwin H. Hall discovered that a small transverse voltage appeared across a current-carrying thin metal strip in an applied magnetic field. 8. How can you tell if a Hall sensor is bad?Loss of power, loud noise and the feeling that the motor is somehow blocked are often signs that either the controller is dead or that you may have issues with the hall sensors inside the motor. 9. What is inside a Hall effect sensor?The Hall effect sensor is a thin sliver of semiconductor material just like the chip inside a micro or RAM devise. It works on the electromagnetism principle. When you move a magnet close enough to the sensor generates a small voltage. This goes to an amplifier which boosts the voltage high enough to be used by other electronic devices. The best example is the wheel speed sensor. A small magnet is attached to the inside of a car wheel. Every time the magnet moves past the sensor that is one rotation of the wheel. The information is passed to the speedometer and odometer unit where it is displayed to the driver. 10. What is a hall effect sensor for on a vehicle?A hall effect sensor operates by a magnetic field and can also be referred to as a crank position sensor. It checks the crankshaft position for the engine to fire the spark plugs. If it is bad, the engine might stall and would not start without the signal from the Hall effect sensor. Hall effect sensors can also be used to determine speed, distance, or engine crankshaft position and camshaft position. All hall effect sensors have different electronics internally with different program measurements and are not interchangeable.

Executive Summary: Proximity Sensors in 2026What is a proximity sensor? A non-contact device that detects the presence or distance of an object using electromagnetic fields, light, or sound waves. Essential for Industry 4.0 automation, robotics, and consumer electronics.Key Types: Inductive (Metals), Capacitive (Non-metals/Liquids), Ultrasonic (Distance/Clear objects), Photoelectric (Long-range), and IR (Short-range).2026 Trends: Integration with IO-Link for predictive maintenance, miniaturized MEMS technology, and AI-driven signal processing for higher accuracy in harsh environments.Ⅰ What is a Proximity Sensor? (2026 Overview)A proximity sensor is a non-contact electronic instrument that detects the presence, proximity, or exact distance of an object without physical contact. In the 2026 landscape of industrial automation, these sensors serve as the "eyes" of machines, ensuring precise control in manufacturing, robotics, and smart devices.While there are many types of proximity sensors, they share a common operational principle: they transmit an electromagnetic field, electrostatic field, or beam of light, and analyze the reflection or field disruption to confirm if an object (the target) is approaching, leaving, or present. The maximum detection limit is defined as the "rated range." Modern smart sensors allow this range to be dynamically adjusted via software protocols like IO-Link. Proximity sensors are renowned for high reliability and zero mechanical wear, as the lack of physical contact prevents component fatigue, giving them a functional lifespan often exceeding 100,000 hours in industrial settings. The five primary categories utilized in 2026 include:Inductive: For ferrous and non-ferrous metals.Capacitive: For liquids, plastics, and powders through barriers.Ultrasonic: For sound-based distance measurement.Photoelectric: For long-range light detection.Hall Effect: For magnetic field detection. Ⅱ How Does a Proximity Sensor Function?Proximity sensors work by emitting a specific field or signal (electromagnetic, electrostatic, or acoustic) and measuring changes in the return signal caused by a target object.2.1 Inductive Sensor PrincipleInductive sensors generate an electromagnetic field via an internal oscillator. When a conductive metal object enters this field, eddy currents are induced in the target, causing a dampening of the oscillation amplitude. The sensor detects this energy loss to trigger a switch.2.2 Capacitive Sensor PrincipleCapacitive sensors function as an open capacitor. They generate an electrostatic field between the sensing electrode and the ground. When any object (metal, water, plastic) enters this field, the capacitance increases, changing the oscillation frequency. Once this frequency crosses a DC voltage threshold, the sensor activates. Ⅲ Detailed Types of Proximity SensorsChoosing the right sensor depends on the target material and environment. Below is the breakdown of the industry standards for 2026.3.1 Inductive Proximity Sensor (Metal Detection)Best for: Harsh industrial environments, detecting machine parts, gears, and cams. Inductive sensors remain the backbone of heavy industry. They utilize a coil-wound oscillator to create a high-frequency magnetic field. They are robust, impervious to oil, dirt, and water (often rated IP67/IP69K), and rely on the principle of induction (Faraday's Law).  Key Characteristics:Target: Metals only (Iron, Steel, Aluminum, Copper).Range: Short (typically 1mm to 60mm).Speed: High switching frequency (up to 5 kHz), ideal for counting rotating gears.Ferrous vs. Non-Ferrous: Detection distance is greatest for ferrous metals (iron) and reduced for non-magnetic metals (aluminum) unless "Factor 1" sensors are used. 3.2 Capacitive Proximity Sensor (Versatile Detection)Best for: Level detection through container walls, detecting plastics, liquids, and granulars. Unlike inductive sensors, capacitive units detect changes in dielectric constant, allowing them to sense virtually any material. They contain two charging plates (internal and external/sensing face). When a target approaches, it alters the dielectric capacity, triggering the switch. Pros & Cons:See-Through Ability: Can detect water inside a plastic tank or powder inside a glass tube.Speed: Slower than inductive (10 to 50 Hz).Sensitivity: Can be adjusted to ignore thin container walls while detecting the contents. 3.3 Ultrasonic Proximity Sensor (Sound Waves)  Best for: Transparent objects (glass, clear plastic), long distances, and difficult lighting conditions. Ultrasonic sensors utilize echolocation—similar to bats or dolphins. A piezoelectric transducer emits a high-frequency sound pulse (chirp) and measures the "Time of Flight" (ToF) for the echo to return. Advantages in 2026:Color Immunity: Unlike optical sensors, color or transparency does not affect accuracy.Distance: Capable of detecting objects several meters away.Blind Spots: While effective, they have a "dead zone" immediately in front of the sensor face.  Limitations: Performance can be impacted by air turbulence, foam on liquids, or extreme temperature fluctuations (which alter the speed of sound), though modern units include temperature compensation. 3.4 IR Proximity Sensor (Infrared) Best for: Short-range detection, security systems, and mobile devices. IR sensors emit a beam of infrared light. If an object is present, the light reflects back to a photodetector at a specific angle (triangulation). These are cost-effective but can be confused by ambient sunlight or dark surfaces that absorb light rather than reflect it. 3.5 Photoelectric Sensor (Optical)Best for: Long-range detection, packaging lines, and logistics.  Photoelectric sensors use a light transmitter (LED or Laser) and a receiver. They are modulated to specific frequencies to avoid interference from ambient light.  Three Key Configurations:Through-Beam: Emitter and receiver are separate. Detects when the beam is broken. Longest range (up to 50m+).Retroreflective: Emitter and receiver in one unit; requires a reflector. Medium range.Diffuse: Light reflects off the object itself. Short range, but easy to install. Ⅳ Key Applications in Industry 4.0  By 2026, proximity sensors are integral to the Industrial Internet of Things (IIoT):Automotive & EV Manufacturing: Inductive sensors detect chassis positioning and gear rotation speeds with extreme precision.Food & Beverage: Capacitive sensors monitor liquid levels in bottles and grain levels in silos through sight glass.Logistics & Warehousing: Photoelectric sensors trigger conveyor belts and size parcels for automated sorting.Smart Electronics: Mobile phones use proximity sensors (often IR or Time-of-Flight/LiDAR) to disable touchscreens during calls or for facial recognition.Vibration Monitoring: Analog proximity sensors measure shaft runout and vibration in large turbines to predict maintenance needs.  Ⅴ Buyer's Guide: How to Choose a Proximity SensorSelecting the correct sensor requires analyzing the target material, environmental constraints, and required range. Use this 2026 decision matrix: Selection CriteriaKey ConsiderationsRecommended Sensor TechnologyTarget Material• Is the object Metal?• Is it Non-Metal (Plastic, Liquid, Wood)?• Is it Transparent (Glass, Clear Film)?• Metal: Inductive (Best reliability)• Non-Metal/Liquids: Capacitive• Transparent: UltrasonicEnvironment• Is it dirty, oily, or dusty?• Are there extreme temperatures?• Is washdown required (IP69K)?• Dirty/Oily: Inductive or Capacitive (Excellent immunity)• Clean/Dry: Photoelectric or IR• Avoid in Dust/Smoke: Optical sensorsSensing Range• Very Close (<50mm)• Medium Range (50mm - 2m)• Long Range (>2m)• Close: Inductive / Capacitive• Medium: Diffuse Photoelectric / Ultrasonic• Long: Through-beam Photoelectric / LiDAR  Ⅵ Frequently Asked Questions (FAQ)1. What does a proximity sensor do in simple terms?It detects if an object is nearby without touching it. This triggers an action, like stopping a machine for safety, counting items on a conveyor, or turning off your phone screen when you hold it to your ear. 2. Which sensor detects plastic or water?Capacitive proximity sensors are the industry standard for detecting non-metallic objects like plastic, glass, wood, and liquids (water, oil, chemicals). 3. Can inductive sensors detect aluminum?Yes, but with reduced range compared to ferrous metals like iron or steel. However, modern "Factor 1" inductive sensors can detect aluminum and steel at the same distance. 4. What is the typical range of a proximity sensor?Inductive and Capacitive sensors typically work between 1mm and 60mm. Ultrasonic sensors can measure up to several meters, and Photoelectric sensors can reach 50+ meters in through-beam configurations. 5. Are ultrasonic sensors affected by color?No. Since they use sound waves, ultrasonic sensors are color-blind. They are ideal for detecting clear glass, black plastic, or highly reflective surfaces that confuse optical sensors. 6. What is the difference between NPN and PNP sensors?This refers to the output transistor type. PNP sensors switch the positive voltage to the output (common in Europe/USA), while NPN switches the negative/ground (common in Asia). 7. How accurate are modern proximity sensors?High-end inductive sensors in 2026 offer repeatability down to 0.001mm (1 micron), making them suitable for precision CNC machining and quality control.{ "@context": "https://schema.org", "@type": "Article", "headline": "Proximity Sensors Explained: Types, Principles, and Applications (2026 Guide)", "datePublished": "2021-04-14", "dateModified": "2026-01-07", "description": "A comprehensive guide to proximity sensors in 2026. Learn about Inductive, Capacitive, Ultrasonic, and Photoelectric sensors, their working principles, and how to choose the right one for industrial automation.", "articleBody": "What is a Proximity Sensor? A proximity sensor is a non-contact electronic instrument that detects the presence, proximity, or exact distance of an object without physical contact...", "mainEntity": { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What does a proximity sensor do?", "acceptedAnswer": { "@type": "Answer", "text": "A proximity sensor detects the presence or absence of an object without physical contact. It emits an electromagnetic field, light, or sound and measures the reflection or disruption to trigger a signal. 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IntroductionPhotoelectric sensor is a sensor that uses a photoelectric component as a conversion element. In electronics, the photoelectric sensor converts the light intensity into the electrical signals. It is generally composed of three parts: transmitter, receiver and detection circuit.The transmitter emits a light beam to the target, and the emitted light beam is generally a semiconductor light source, such as a light emitting diode (LED), a laser diode, and an infrared emitting diode. The beam is emitted continuously, or change the pulse width to accomplish it. The receiver is composed of a photodiode, a phototransistor, and a photocell commonly. In front of the receiver, optical components such as lens and aperture are installed. Behind it is the detection circuit, which can filter out the effective signal and make actions.What is Photoelectric Sensor?CatalogIntroductionⅠ Photoelectric Sensor Basic1.1 Photoelectric Sensor Characteristics1.2 Photoelectric Effect1.3 Optical Signals into Electrical SignalsⅡ Photoelectric Sensor Applications2.1 What are Photoelectric Sensors Used?2.2 Example: Infrared Photoelectric Sensor SwitchⅢ Photoelectric Sensor Development3.1 Advantages3.2 Smart Photoelectric SensorsⅣ Frequently Asked Questions about Photoelectric SensorⅠ Photoelectric Sensor Basic1.1 Photoelectric Sensor CharacteristicsPhotoelectric sensors can be used to detect non-electrical physical quantities that directly cause changes in light, such as light intensity, illuminance, radiation temperature measurement, gas composition analysis, etc., and can also be used to detect other non-electrical quantities that can be converted into light quantity changes, such as part diameter, surface roughness, displacement, vibration, speed, acceleration, as well as the recognition of the shape and working state of the object. It has the characteristics of non-contact, fast response, reliable performance, etc., So it is widely used in industrial automation devices and robots.1.2 Photoelectric EffectThe principle of photoelectric sensors is usually divided into three categories: (1) The phenomenon that can cause electrons to overflow the surface of an object under the action of light is called external photoelectric effect, such as photoelectric tube, photomultiplier tube, etc.(2) Under the action of light, the change of resistance is called the internal photoelectric effect, such as photoresistor, phototransistor, etc.(3) An object generates a certain directional electromotive force under the action of light is called the photovoltaic effect, such as photovoltaic cells.1.3 Optical Signals into Electrical SignalsPhotoelectric sensors that use photoelectric components based on photoelectric effect as sensing parts have a wide variety of applications. According to the nature output of the device, it has two principles:1) A continuously changing photocurrent can be used to measure the intensity of light and physical quantities such as temperature, light transmission ability, displacement and surface state of the object. For example: illuminance meter for measuring light intensity, photoelectric pyrometer, photoelectric colorimeter and turbidity meter, photoelectric alarm, automatic detection device for quality testing products. Semiconductor optoelectronic components are not only widely used in the civil industry, but also have an important role in the military. For example, lead sulfide photoresistors can be made into infrared night vision devices, infrared cameras and infrared navigation systems.2) Convert the measured stuff into a continuously changing photocurrent. Various photoelectric automatic devices are made with the characteristics of "with" or "without" electrical signal output when photoelectric elements are irradiated by light or no light. The photoelectric element is used as a switch-type photoelectric conversion element. For example, the photoelectric input device of the electronic computer, the switch type temperature adjusting device and the digital photoelectric speed measuring instrument, etc.Based on the above mentioned, the sensing types of photoelectric sensor include through-beam arrangement, reflective arrangement, laser-reflective, and diffuse type.Ⅱ Photoelectric Sensor Applications2.1 What are Photoelectric Sensors Used?1) Smoke and Dust Concentration MonitorPreventing industrial smoke and dust pollution is one of the important tasks of environmental protection. To eliminate it, we must first know the amount of smoke and dust emissions. Therefore, the source of the smoke and dust must be monitored, automatically displayed and alarmed for exceeding the standard. The turbidity of the smoke and dust in the flue is detected by the size of the change during the transmission of light in the flue. If it increases, the light emitted by the light source is absorbed and refracted by the soot particles, and the light reaching the photodetector decreases. Therefore, the strength of the output signal of the photodetector can reflect the change of flue turbidity.2) Barcode ScannerWhen the scanning pen moves on the bar code, if it encounters a black line, the light of the light-emitting diode will be absorbed by the black line, and the phototransistor will not receive the reflected light, present a high impedance and be in a cut-off state. When encountering the white interval, the light emitted by the LED is reflected to the base of the photosensitive triode, which generates a photocurrent to conduct. After the entire bar code is scanned, the phototransistor deforms the bar code into electrical pulse signals, which are amplified and then reshaped to form a pulse train, and finally processed by a computer to complete the identification of the bar code information.3) Product CounterWhen the product is running on the conveyor belt, it continuously shields the light path from the light source to the photoelectric sensor, so that the photoelectric pulse circuit generates an electrical pulse signal. Every time the light is shaded by products, the photoelectric sensor circuit generates a pulse signal. Therefore, the number of output pulses represents the number of products. The pulse is counted by the counting circuit and displayed by the display circuit.4) Photoelectric Smoke DetectorWhen there is no smoke, the light emitted by the LED travels in a straight line, and the phototransistor does not receive a signal. When there is no output, but having smoke, the light emitted by the light-emitting diode is refracted by the smoke particles, so that the triode receives the light, a signal output sends an alarm.5) Measuring SpeedCoated with black and white on the rotating shaft of the motor. When rotating, the reflected light and non-reflected light alternately appear. The photoelectric sensor correspondingly intermittently receives the reflected light signal, and outputs the intermittent electrical signal, which is amplified by the amplifier and the shaping circuit. The square wave signal is shaped and output, and finally the motor speed is output by the electronic digital display.6) Photocells in Photoelectric Detection and Automatic ControlWhen photocells used as photodetectors, their basic principles are the same as photodiodes, but their basic structures and manufacturing processes are not exactly the same. Since the photovoltaic cell does not require an external voltage when working, it has the advantages of high photoelectric conversion efficiency, wide spectral range, good frequency characteristics, low noise, etc. They are widely used in photoelectric readout, photoelectric coupling, grating ranging, laser collimation, film sound recovery, UV monitors and flameout protection devices for gas turbines, etc.2.2 Example: Infrared Photoelectric Sensor SwitchUses the blocking or reflection of the infrared light beam by the measured object to detect whether there is an object under test. When the detected object passes through the detection area, the output state of the infrared photoelectric switch will be change to achieve automatic detection. Moreover, objects that have the ability to reflect and block infrared light can be detected.Photoelectric Sensor Switch Design: Parameters and DrawingsParametersDescriptionsCurrent Consumption5mA~30mAOutput CurrentDC: less than 200mA  AC: less than 200mA  Relay Outputs, Contact Current: 1A~3AResponse TimeDC: less than 2.5ms AC: less than 30msDetect ObjectTransparent, OpaqueOpaqueTransparent, OpaqueOpaqueDifferential DistanceLess than 20% Less than 20% Pointing Angle 3°~20°3°~10° 3°~20°3°~10°Environmental IlluminanceSurface Light Intensity: Less than 3000lx (filament lamp)  Less tan 10000lx (sun light)Insulation ResistanceOver 200MΩⅢ Photoelectric Sensor Development3.1 Advantages① Long Detection DistanceIf the detection distance of 10m or more is set in the through-beam type, it can detect remotely that other detection methods (magnetic, ultrasonic, etc.).② Less Restrictions on Detecting ObjectsAs the detection principle is based on the shading and reflection caused by the detection object, unlike proximity sensors, which limit the detection object to metal. Photoelectric sensor can detect almost all objects such as glass, plastic, wood, and liquid.③ Short Response TimeThe light itself is high speed, and the circuit of the sensor is composed of electronic parts, so there is no mechanical working time, and the response time is very short.④ High ResolutionHigh-resolution can be achieved by using advanced design technology to concentrate the projected light beam on a small spot, or by forming a special light-receiving optical system. It can also detect small objects and high-precision position.⑤ Non-contact DetectionThe detection can be achieved without mechanically touching the detection object, so it will not cause damage to the detection object and the sensor. Therefore, the photoelectric sensor can be used for a long time.⑥ Color DiscriminationThe reflectance and absorptivity of the light formed by the detection object differ according to the combination of the wavelength of the light projected and the color of the detection object. Using this characteristic, the color of the detected object can be detected.⑦ Easy to AdjustIn the type of projected visible light, because the projected light beam is visible to the eyes, the position of the detection object can be moved easily.3.2 Smart Photoelectric SensorsDiscover the best Photoelectric Sensors in the future. Smart photoelectric sensors provide essential input for every process chain. They support dynamic, real-time-optimized, and self-organized industry processes. The functions of the smart photoelectric sensor are: self-compensation, self-calibration, self-diagnosis, numerical processing, two-way communication, information storage, and digital output. With the development of science and technology, the functions of smart photoelectric sensors will gradually increase. It will use artificial neural networks, artificial intelligence, and information processing technologies (such as sensor information fusion technology, fuzzy theory, etc.) to enable sensors to have more advanced intelligence, analysis skill, and judgment. So its self-adaptation and self-learning functions can complete complex tasks such as image recognition, feature detection, and multi-dimensional detection. Ⅳ Frequently Asked Questions about Photoelectric Sensor1. What is a photoelectric sensor?A photoelectric sensor is a device that detects a change in light intensity. Typically, this means either non-detection or detection of the sensor's emitted light source. 2. How does a photoelectric sensor work?A Photoelectric Sensor consists primarily of an Emitter for emitting light and a Receiver for receiving light. When emitted light is interrupted or reflected by the sensing object, it changes the amount of light that arrives at the Receiver. The Receiver detects this change and converts it to an electrical output. 3. Where are photoelectric sensors used?Checking objects on production lines or conveyors: photoelectric sensors can detect items' sizes to spot any errors, or simply spot their absence, as well as picking up problems like misaligned caps on bottles. They are widely used in the food and pharmaceutical industries, and in packaging plants. 4. What are the three types of photoelectric devices?There are three major types of photoelectric sensors: thru-beam, retroreflective, and diffused. Each sensor has its own strengths and can be used in a variety of ways. 5. What are the two basic components of a photoelectric sensor?Basically, there are two major components in the photoelectric sensor. They are a transmitter (light source) and receiver (sensor). 6. What are the three basic parts of the photoelectric sensor?A photoelectric sensor is constructed of a light source, light receiver, the main circuit, and an output circuit, and the parts have the following functions respectively. The photodiodes and phototransistors of the light receiver receive the light emitted from the light source and convert it to an electrical signal. 7. What is a photoelectric switch sensor?A photoelectric sensor is a type of switch. It is a switch that is. turned off and on by the presence or absence of received light. The inherent advantages of such a 'non-contact' switch have. resulted in widespread application throughout the industry. 8. What is the use of a photoelectric sensor?A photoelectric sensor emits a light beam (visible or infrared) from its light-emitting element. A reflective-type photoelectric sensor is used to detect the light beam reflected from the target. A thru beam-type sensor is used to measure the change in light quantity caused by the target crossing the optical axis. 9. How do I connect my photoelectric sensor?Connect one black wire on the photocell to the black wire that comes from the building. Be sure to twist the exposed copper wire so that it forms a tight connection. Connect the second black wire on the photocell to the black wire on your light fixture, making sure that the copper wire is twisted together completely. 10. How do you test a photoelectric sensor?The easiest way to determine how your photocell works is to connect a multimeter in resistance-measurement mode to the two leads and see how the resistance changes when shading the sensor with your hand, turning off lights, etc. Because the resistance changes a lot, an auto-ranging meter works well here. 

Ⅰ IntroductionThere are 400 types of scent receptors in a typical human nose that allow us to detect about 1 trillion different odors. But many of us also can't define the form or concentration of gas in our atmosphere. There are several kinds of sensors to calculate various parameters and a gas sensor is one that is useful in applications where we have to detect changes in the concentration of harmful gases to keep the device safe and prevent any unwanted threats. To detect gases such as oxygen, carbon dioxide, nitrogen, methane, etc., there are different gas sensors. They can also be widely used in devices that are used in factories and offices to detect the leakage of toxic gases, track air quality, etc. We will learn more about gas sensors, their construction, types, function, and how they can be used to calculate the type and concentration of gas required in our atmosphere in this article. There are several kinds of gas sensors, but gas sensors of the MQ type are frequently used and widely popular, so this article will concentrate more on these types of sensors.CatalogⅠ IntroductionⅡ Introduction of Gas SensorⅢ Different Types of Gas sensorsⅣ Construction of Gas SensorⅤ Working of Gas SensorⅥ Working Principle of Gas SensorⅦ How can a gas sensor be used?Ⅷ Gas Sensors List and What Gases They SenseⅨ Gas Sensors ApplicationsⅩ FAQⅡ Introduction of Gas SensorA gas sensor is a device that senses the atmosphere's presence or concentration of gases. The sensor creates a corresponding potential difference depending on the concentration of the gas by adjusting the resistance of the material within the sensor, which can be determined as the output voltage. The type and concentration of the gas can be calculated based on this voltage value.The type of gas that can be detected by the sensor depends on the sensing material within the sensor. As shown above, these sensors are usually available as modules with comparators. A specific threshold value of the concentration of gas may be set for these comparators. The automated pin goes up when the concentration of the gas reaches this threshold. It is possible to use the analog pin to measure the gas concentration.Ⅲ Different Types of Gas sensorsBased on the type of sensing element it is designed with, gas sensors are usually categorized into different categories. Below is the classification based on the sensing aspect of the different types of gas sensors that are commonly used in different applications:• Metal Oxide Based Gas Sensor.• Optical Gas Sensor.• Electrochemical Gas Sensor.• Capacitance-based Gas Sensor.• Calorimetric Gas Sensor.• Acoustic Based Gas Sensor.Ⅳ Construction of Gas SensorThe Metal Oxide Semiconductor Based Gas Sensor is the most widely used gas sensor of all the above types. A sensing component containing the following elements will consist of all gas sensors.• Gas Sensing Layer• Heater Coil• Electrode Line• Tubular Ceramic• ElectrodeThe picture below shows the components of a metal oxide gas sensor.The goal of each of these elements is as shown below.:• Gas sensing layer: It is the main component of the sensor that can be used to detect changes in gas concentration and produce electrical resistance changes. The gas sensing layer is essentially a chemical resistor that adjusts its resistance value depending on the environment's real gas concentration. The sensing factor consists of a Tin Dioxide (SnO2) here, which generally has excess electrons (donor element). Therefore, the resistance of the element changes and the current flown through it varies as toxic gases are detected, which reflects the shift in gas concentration. • Heater coil: The purpose of the heater coil is to burn the sensing component to increase the sensitivity and efficiency of the sensing component. It is made of nickel-chromium with a high melting point that allows it to remain heated without melting. • Electrode line: Since a very small current is generated by the sensing element when the gas is detected, preserving the efficiency of carrying those small currents is more critical. So Platinum wires come into play where they help to efficiently transfer the electrons. • Electrode: It is a junction where the sensing layer output is attached to the line of the electrode. So that the output current may flow to the terminal that is needed. Gold (Au-Aurum), which is a very good conductor, is an electrode here. • Tubular ceramic: There is a tubular ceramic made from aluminum oxide between the heater coil and the gas sensing layer (Al2O3). As it has a high melting point, it helps to preserve the sensing layer's burn-in (preheating), which provides the sensing layer with high sensitivity to obtain an effective output current. • Mesh over the sensing element: A metal mesh is used over it to cover the sensing elements and the setup, which is also used to prevent/hold dust particles from entering the mesh and to prevent damage from corrosive particles to the gas sensing layer.Ⅴ Working of Gas SensorA gas sensor's ability to detect gases relies on the chemiresistor to conduct current. Tin Dioxide (SnO2), which is an n-type semiconductor with free electrons, is the most widely used chemical resistor (also called a donor). The atmosphere usually contains more oxygen than combustible gases. The particles of oxygen attract the free electrons present in SnO2, bringing them to the surface of SnO2.  As there are no free electrons available, there will be a zero output current. The gif below shows the oxygen molecules (blue color) within the SnO2 attracting the free electrons (black color) and preventing them from having free electrons to perform the current.Ⅵ Working Principle of Gas SensorThis decreasing gas (orange color) interacts with the adsorbed oxygen particles when the sensor is put in the atmosphere of toxic or combustible gases and breaks the chemical bond between oxygen and free electrons, thereby releasing free electrons. As the free electrons return to their original location they will now conduct current, this conduction would be proportional to the number of free electrons available in SnO2 if more free electrons are available for the gas to be highly toxic.Ⅶ How can a gas sensor be used?There are 6 terminals in a simple gas sensor in which 4 terminals (A, A, B, B) serve as input or output and the remaining 2 terminals (H, H) are used to heat the coil. Of these 4 terminals, 2 terminals from each side can be used as either input or output (as seen in the circuit diagram, these terminals are reversible) and vice versa.MQ2 Gas sensor PinoutThese sensors are usually available as modules (shown on the right), consisting of a gas sensor and an IC comparator. Now let's see the gas sensor module pin definition that we normally use with an Arduino. The module for the gas sensor consists of 4 terminals.• Vcc – Power supply• GND – Power supply• Digital output – This pin produces an output that is either logically high or logically low (0 or 1), indicating that it shows any harmful or combustible gases near the sensor.• Analog output – This pin provides a continuous voltage output that varies depending on the gas concentration added to the gas sensor.The output of a gas sensor alone would be very small (in mV) as discussed earlier, so an external circuit has to be used to get a digital high low output from the sensor. A comparator (LM393), adjustable potentiometer, some resistors and capacitors are used for this purpose. The goal of LM393 is to get the sensor output, compare it to a reference voltage, and show whether or not the output is logically high. Whereas the potentiometer is intended to set the gas threshold value needed above which the digital output pin should go high. A simple circuit diagram of a gas sensor in a gas sensor module is shown in the diagram below.The input and output terminals here are A and B (these are reversible - meaning either of the paired terminals can be used as input or output) and H is the terminal for the heater coil. The purpose of the variable resistor is to change the voltage of the output and maintain high sensitivity. If the heater coil has no input voltage, so the output current would be much smaller (which is negligible or approximately 0). The sensing layer wakes up when an appropriate voltage is applied to the input terminal and heater coil and is ready to detect any combustible gases near it. Let's first presume that there is no poisonous gas near the sensor, so the layer's resistance does not shift and the output current and voltage are also unchanged and insignificant (approximately 0). Now, let's say that poisonous gas is nearby. Since the heater coil is pre-heated, any combustible gases can now be easily detected. The resistance of the material varies as the sensing layer interacts with the gases, and the current flowing through the circuit often varies. This variation shift can then be observed in the load resistance (RL). The load resistance (RL) value can be anywhere from 10K to 47K. It is possible to pick the exact value of the load resistance by calibrating it with the known gas concentration. The circuit has lower sensitivity if the low load resistance is chosen, and if the high load resistance is selected, then the circuit has high sensitivity.Ⅷ Gas Sensors List and What Gases They SenseSensor NameGas to measureMQ-2Methane, Butane, LPG, SmokeMQ-3Alcohol, Ethanol, SmokeMQ-4Methane, CNG GasMQ-5Natural gas, LPGMQ-6LPG, butaneMQ-7Carbon MonoxideMQ-8Hydrogen GasMQ-9Carbon Monoxide, flammable gassesMQ131 Ozone............Ⅸ Gas Sensors Applications• It is used to track the concentration of toxic gases in industries.• Used in homes to recognize activities in an emergency.• The concentration of the gases that are emitted is tracked at oil rig locations.• Used at hotels to discourage smoking by clients.• Used in workplace air quality inspections.• It is used to track CO2 levels in air conditioners.• Used in fire detection.• Used for gas concentration regulation in mines.• The analyzer of breath.Ⅹ FAQ1. What is a gas sensor?As the name suggests, it senses gas. It's a component used to detect fluctuations in the gaseous state. There are so many gas sensors based on the element they sense, some are given below:• Carbon Dioxide Sensor: Used for detection of pollution caused by vehicles emitting CO2.• Alcohol Sensor: I know alcohol is not a gas but it senses the smell of it. Traffic police use devices based on this sensor.• LPG Sensor: It is used for avoiding the destruction caused by leaked LPG cylinders. 2. What are gas sensor arrays?A gas sensor that is commonly available in the market is an MQ-x series sensor - MQ2, MQ3, MQ6, etc. The module for this series sensor gives a digital output but can even be modified to have an analog output. MQ2 sensor can detect gasses like propane, butane, LPG, smoke and alcohol. An array of gas sensors would mean that all the sensors of this category are interfaced to the same controller and are laid at different locations to monitor the aspect. 3. How does a gas sensor work?Gas detectors use a sensor to measure the concentration of particular gases in the atmosphere. The sensor serves as a reference point and scale, producing a measurable electric current when a chemical reaction caused by a specific gas occurs. 4. How do MQ5 gas sensors work?In any sensor, a physical change contributes to a chemical change that generates an electrical impulse which then drives a circuit.Similarly here, the MQ5 gas sensor which is made of SnO2 is less conductive normally. In LPG or any combustible gas environment like propane-butane etc., it becomes more conductive.A circuit similar to the Wheatstone bridge will be available inside the sensor with one of its resistance made of SnO2. Assume a bridge balanced condition. When the conductivity changes bridge becomes unbalanced. Hence current flows through the center galvanometer showing deflection.  5. What is the difference between a gas analyzer and a gas detector?A gas detector has simple structures, consisting only of the sensor and sensor conversion circuit. However, a gas analyzer not only has sensors inside but also has a complete set of pneumatic systems, which introduces the sample gas into the instrument firstly and then discharges or retrieves the gas. 6. What is the use of a gas sensor?Gas sensors (also known as gas detectors) are electronic devices that detect and identify different types of gasses. They are commonly used to detect toxic or explosive gasses and measure gas concentration. 7. How long do gas detectors last?The typical life span of an electrochemical sensor is usually between 2-3 years. Whereas a more exotic gas sensor may only last 12-18 months. I would advise anyone who uses a gas detector to get the instrument serviced every 6 months as this will ensure that your instrument will be working perfectly. 8. What is gas sensor sensitivity?Usually, sensitivity (S) can be defined as Ra/Rg for reducing gases or Rg/Ra for oxidizing gases, where Ra stands for the resistance of gas sensors in the reference gas (usually the air) and Rg stands for the resistance in the reference gas containing target gases. 9. What is the most important sensor in a gas monitor?The most important technical aspect of all gas detectors is the heart of the instrument - the sensor. All the bells and whistles that can be crammed into one instrument can't take away from the simple fact that sensors must technically process incoming gases and vapors and provide an accurate response. 10. What is a gas sensor made of?Highly sensitive and selective sensors are needed for the detection and prevention of hazardous gas leaks from industries. Generally used gas-sensing materials comprise vapor-sensitive polymers, semiconductor metal oxides, and other porous materials such as silicon.

IntroductionThe mass air flow sensor, also known as the air flow meters, is one of the important sensors of the electronic jet engine. It converts the inhaled air flow into electrical signals and sends them to the Electronic Control Unit (ECU). As one of the basic signals to determine fuel injection, it is a sensor to measure the inhaled air flow into the engine.      CatalogIntroductionCatalogⅠ OverviewⅡ Structural PrincipleⅢ The Structure of the Valve Type Air Flow SensorⅣ Karman Scroll Air Flow SensorⅤ Measuring RangeⅥ Detection PrincipleⅦ Ultrasonic Karman Vortex Air Flow SensorⅧ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionⅨ FAQⅠOverviewIn order to obtain the best concentration of the mixture under various operating conditions, the electronically controlled gasoline injection engine must accurately measure the amount of air inhaled into the engine at each moment, which is the main basis for the ECU to calculate (control) the amount of fuel injection.  If the air flow sensor or circuit fails and the ECU does not get the correct intake signal, it will not be able to control the fuel injection properly, which will cause the mixture to be too thick or too thin, and the engine will not operate properly. There are many types of air flow sensors in the electronic controlled gasoline injection system. According to their structure types, the common air flow sensors can be divided into blade (wing) type, core type, hot-wire type, hot film type, Karman vortex type, etc.                     Ⅱ Structural PrincipleIn the electronic controlled fuel injection device, the mass air flow sensor, which measures the amount of air absorbed by the engine, is one of the important components to determine the control precision of the system. When the control precision of the air-fuel ratio (A/F) of the air and mixture inhaled by the engine is specified as ±1.0, the allowable error of the system is ±6[%]~7[%]. When the allowable error is distributed to each component of the system, the allowable error of the air flow sensor is ±2[%]~3[%]. The ratio of the maximum value to the minimum value of the air flow rate inhaled by a gasoline engine is 40-50 in a natural intake system, and 60-70 in a supercharged system. In this range, the air flow rate of the sensor should be able to maintain a measurement accuracy of ±2~3[%]. The air flow sensor used in the electronic control fuel injection device should not only maintain the measurement accuracy over a wide measurement range, but also have excellent measurement response and can be measured. For pulsating air flow, the output signal processing should be simple. According to the different characteristics of the air flow sensor, the fuel control system is divided into L-type control for direct measurement of air intake volume and D-type control for indirect measurement of air intake volume (indirect measurement of air intake according to the negative pressure of the intake manifold and the engine speed).                                                           The microcomputer ROM in the D-type control mode stores in advance the intake air volume under various conditions based on the engine speed and the pressure in the intake pipe. The microcomputer is based on the measured operation. The intake pressure and speed in the state, referrring to the intake volume memorized by ROM, can calculate the fuel volume. The air flow meter used for L-type control is basically the same as the general industrial flow sensor, but it can adapt to the harsh environment of the car, but it is the response requirements for the rapid changes in the flow rate that occur during the throttle and the requirements for high-precision detection in the uneven airflow caused by the shape of the intake manifold before and after the sensor. The original electronic fuel injection control system did not use a microcomputer. It was an analog circuit. At that time, a valve-type air flow sensor was used, but several other air flow sensors emerged as microcomputers were used to control fuel injection.Ⅲ The Structure of the Valve Type Air Flow SensorThe valve type air flow sensor is mounted on the gasoline engine and installed between the air filter and the throttle. Its function is to detect the air intake of the engine and convert the detection results into electrical signals, which are then input into the microcomputer. The sensor is composed of an air flow meter and potentiometer. Look at the working process of the air flow sensor first. The air drawn in by the air filter rushes to the valve, and the valve turns to stop at the position where the intake is balanced by the return spring. In other words, the opening of the valve is proportional to the intake.  A potentiometer is also installed on the rotating shaft of the valve, and the sliding arm of the potentiometer rotates synchronously with the valve. The voltage drop of the sliding resistance is used to convert the opening of the measuring piece into an electrical signal, which is then input into the control circuit.Ⅳ Karman Scroll Air Flow SensorIn order to overcome the shortcomings of the valve type air flow sensor, that is, under the premise of ensuring measurement accuracy, expanding the measurement range and eliminating the sliding contact, a small and lightweight air flow sensor has been developed, namely the Karman Vortex Air Flow Sensor. The Karman vortex is a physical phenomenon. The vortex detection method and electronic control circuit have nothing to do with the detection accuracy. The air path area and the size change of the vortex column determine the detection accuracy. Because the output of such a sensor is an electronic signal (frequency), the AD converter can be eliminated when the signal is input to the control circuit of the system. Therefore, in essence, the Karman vortex air flow sensor is a signal suitable for microcomputer processing. This sensor has the following three advantages: high test precision, which can output linear signal and signal processing is simple; long-term use and performance will not change; because it detects volume flow, it does not need to correct temperature and atmospheric pressure.                                     The principle of flow detection of this air flow sensor is that when a Karman vortex is generated, it follows the change of speed and pressure. The basic principle of flow detection is to make use of the velocity change. The signal waveform output from the air flow sensor to the control module is shown in the figure. The signal is a square wave and a digital signal. The more air intake, the higher the frequency of the Karman vortex, and the higher the frequency of the output signal of the air flow sensor. The temperature and pressure compensation air flow sensor, mainly used for industrial pipeline flow measurement of medium fluid, such as gas, liquid, vapor and other media. It is characterized by small pressure loss, large range, high precision, and is almost unaffected by fluid density, pressure, temperature, viscosity and other parameters when measuring volume flow in working conditions.Features of the Karman Vortex Flow Meter                                There are no movable mechanical parts, so the reliability is high and the maintenance is small. The instrument parameters can be stable for a long time. This instrument adopts piezoelectric stress sensor, which has high reliability and can work in the working temperature range of -10℃~+300℃. There are analog standard signals and digital pulse signal outputs, which are easy to use with digital systems such as computers. It is a relatively advanced and ideal flow. The biggest advantage of the air flow sensor is that the meter coefficient is not affected by the physical properties of the measuring medium, and can be extended from a typical medium to other mediums. However, the frequency range is also very different because of the great difference between liquid and gas velocity ranges. In the amplifier circuit that processes the vortex signal, the passband of the filter is different, and the circuit parameters are also different. Therefore, the same circuit parameter cannot be used to measure different media.Ⅴ Measuring Range             Ⅵ Detection PrincipleOverhead power lines in the field whine when blown by the wind. The higher the wind speed is, the higher the sound frequency will be. This is because the air flows through the wire and forms a vortex. This phenomenon can occur in liquid, gas and other fluids, which can be used to make a vortex flow sensor. After the column is placed in the tube, two rows of vortices are formed, and the flow rate can be measured according to the frequency of occurrence of the vortices. Because the vortex turns into two parallel rows and alternates left and right, similar to the street lights on both sides of the street, it is called the vortex street. Because this phenomenon was first discovered by Karman, it is also called Karman Vortex Street.                                  Karman Vortex StreetⅦ Ultrasonic Karman Vortex Air Flow SensorThe ultrasonic air flow sensor is provided with two intake channels, the main channel and the side channel. The detection part of the intake flow is located on the main channel. The purpose of setting the side channel is to adjust the flow of the main channel so as to make the detection characteristics of the main channel present an ideal state. That is to say, for engines with different exhaust volume, one specification of air flow sensor can be used to cover a variety of engines by changing the cross-section size of the air flow sensor channel. The Karman vortex generator is composed of triangular columns and several vortex amplifiers on the main channel. On both sides of the place where the Karman vortex is generated, the ultrasonic transmitter and the ultrasonic receiver belonging to the electronic detection device are arranged oppositely. These two components can also be classified into the sensor. The electrical signal generated by the two electronic sensors is passed through the air. The control circuit (hybrid integrated circuit) of the flow sensor is shaped and amplified into an ideal waveform, and then input to the microcomputer. In order to detect vortices by ultrasound, sound-absorbing materials are glued to the inner wall of the vortex channel to prevent irregular reflections of ultrasonic waves.Ⅷ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionThe vortex occurs alternately from both ends of the vortex generator, so the pressure at both ends of the vortex generator also alternately changes. This pressure change is guided to the mirror cavity through the pressure guide hole on the cone-shaped column on the downstream side of the vortex generator. In the mirror cavity, the mirror in the mirror cavity is tensioned with a very thin tension band, so distortion and vibration appear on the tension band. In addition, a leaf spring is used to apply appropriate tension to the tension band. Pressure changes other than vibration and scroll pressure are difficult to affect, so stable torsion and vibration can be obtained. The pressure formed by the vortex passes through the pressure guide hole to the reflector cavity, and the pressure changes synchronously with that in the reflector, and the reflector twists and vibrates in the tension band. The reflector is very lightweight and can operate even at low flow rates and very small pressure changes. On the upper part of the reflector, a light sensor composed of light-emitting diodes and phototransistors is correspondingly arranged. When the light emitted by the diode is reflected by the reflector and hits the phototransistor, it will become a current and output after the waveform circuit.Ⅸ FAQ1. What is the difference between the MAF sensor and the oxygen sensor?The MAF is the Mass Air Flow sensor and just as the name implies the sensor measures the mass of air going into the engine at the sensor (this is important because vacuum leaks or unmetered air is unaccounted for on the MAF sensor). Typically it uses a heated element and the air moving across the element cools it to "measure" the incoming air, however, vane style meters existed in the earlier days of electronic fuel injection. There are upstream and downstream oxygen sensors. The upstream sensor is responsible for checking the exhaust output of the engine. If there is too much fuel left in the exhaust the O2 sensor sends that information to the ECU and it will "trim" it out. If the O2 sensor samples the exhaust and there is too much oxygen in the exhaust stream then the sensor sends that info to the ECU and it will command more fuel. The downstream O2 sensor is present to monitor the condition of the catalytic converter(s). If it is out of range the ECU will flag it and the check engine light will illuminate. This is a very simple, quick, overview of the sensors but should give you a basic idea of their operation. 2. What are the symptoms of a bad mass airflow sensor?A faulty mass airflow sensor will cause problems similar to low compression or low vacuum, and will also show symptoms similar to when your vehicle has low fuel pressure from a faulty fuel pump. Here are some of the most common symptoms of a faulty mass airflow sensor:The engine is very hard to start or turn overThe engine stalls shortly after startingThe engine hesitates or drags while under load or idleHesitation and jerking during accelerationThe engine hiccupsExcessively rich or lean idling 3. How does a MAF sensor work?Installed in the intake pipe between the air filter housing and the intake manifold, most MAF sensors work on the hot wire principle. Put simply, a MAF has two sensing wires. One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as airflow. The quantity of air entering the engine is adjusted accordingly. 4. Can a car run without a mass airflow sensor?Well, the answer to that is no. If you disconnect the mass airflow sensor, then the car should keep running and still be able to start normally. This means that if your mass airflow sensor dies completely, then your car will stay running and surprisingly the car might run better without the mass airflow sensor. 5. Why a MAF sensor needs to be replaced?If the sensor gets dirty, it won’t be able to read the airflow. When the MAF sensor doesn’t work, the engine may idle roughly, hesitate, and have difficulty starting. It may even stall on you while driving, which is no fun. The most common cause for the sensor to become dirty is an air filter that doesn’t get replaced when needed. When the air filter is clogged, it allows more dirt and debris to slip by and accumulate on the sensor. Routine maintenance and air filter replacement can extend the life of your MAF sensor and ensure it continues to work correctly. While the exact timing varies based on where and how much you drive, a good rule to follow is every 10,000 to 12,000 miles. 6. What will a bad mass airflow sensor do?A contaminated or failed mass air flow sensor cannot measure the amount of air flow correctly. This causes the engine computer to miscalculate the amount of injected fuel. As a result, a bad mass air flow sensor causes various driveability problems, including a no-start, stalling, lack of power and poor acceleration. 7. Will a bad mass airflow sensor cause a misfire?If an oxygen sensor or mass airflow sensor is failing, it could give incorrect data to your engine's computer, causing the misfire. When a vacuum line is broken, it can cause a fuel-injected motor to misfire. ... Replacing a vacuum line that's gone bad can potentially resolve the misfire. 8. How long does it take for the mass air flow sensor to reset?When you change a MAF sensor, you need to disconnect the battery for about 10 minutes so the computer forgets the learned parameters and resets to the factory parameters. Then it goes into learn mode and may take a little while before it learns all the parameters of the new MAF sensor. 9. How long can I drive with MAF unplugged?When you unplug the MAF, the computer goes to a default value stored in your memory. Your fuel economy will probably suffer a little bit, but no big issues. You're OK for a week or two, but replace the MAF with a proper TDI unit. The long-term effect is that the car does not operate to its full potential. 10. Can you bypass a MAF sensor?There is a sensor on the air intake called the mass air flow sensor. This sensor calculates how much air to mix with the fuel. You can bypass the MAF sensor, and allow the O2 sensor to calculate how much air is needed. 

IntroductionIn September of this year, Apple's new generation of watch Apple watch series 6 launched the blood oxygen measurement function. In the following month or two, smart watches with blood oxygen measurement function were released together, vivo WATCH, Huawei Watch GT2, Honor Watch GS Pro, Hua Mi Amazfit GTR 2 and GTS 2 flagship smart watches almost all include this feature. In October, Huami Technology released the Amazfit Pop, which is priced at only 299RMB, and is also equipped with blood oxygen measurement. The blood oxygen sensor has begun to penetrate into low-end and mid-range computers, which may set off a greater wave.So, what exactly is the blood oxygen measurement function on the smart watch? Is it reliable? After you finish reading this article, you will get the answer.CatalogIntroductionCatalogI Blood Oxygen & Blood Oxygen Saturation 1.1 What is Normal Blood Oxygen Level? 1.2 How Important is Blood Oxygen Saturation?II How Does a Smart Watch Measure Blood Oxygen?III What is the use of Measuring Blood Oxygen Saturation?IV Is it Reliable to Measure Blood Oxygen with a Smart Watch?V Comparison with Pulse Oximeter 5.1 What is a Pulse Oximeter? 5.2 How Does a Pulse Oximeter Work? 5.3 Main Components 5.4 Can a Smart Watch be Used as a Pulse Oximeter?VI Is it Necessary to Have an Oximeter at Home During Covid-19? 6.1 Can a Pulse Oximeter Diagnose Covid-19? 6.2 Is it Necessary to Buy a Pulse Oximeter?VII FAQI Blood Oxygen & Blood Oxygen Saturation1.1 What is Normal Blood Oxygen Level?Blood oxygen refers to the oxygen in the blood, and the human body's normal blood oxygen saturation is above 95%. The higher the oxygen content in the blood, the better the human metabolism. Of course, high blood oxygen content is not a good phenomenon. The blood oxygen in the human body has a certain degree of saturation. Too low will cause insufficient oxygen supply in the body, and too high will cause cell aging in the body.Figure1. Blood Oxygen1.2 How Important is Blood Oxygen Saturation?The cells in the human body rely on oxygen to survive. The oxygen that enters the human body through the respiratory system will be combined with hemoglobin and transported to various organs. Blood oxygen saturation is a measure of the percentage of hemoglobin combined with oxygen, so blood oxygen saturation is a key indicator to measure the health of the body. This parameter can be used to understand the oxygen content in the human blood. Under normal circumstances, the normal blood oxygen saturation is between 95% and 100%. If the blood oxygen saturation is less than 90%, it can be considered as hypoxemia. When blood oxygen saturation is too low, it means that there will be hypoxia, which will affect the central nervous system, liver, kidney and other important organs. Therefore, blood oxygen saturation is an important indicator, and the measured data can assist in judging the current physical health.Figure2. How Important is Blood Oxygen Saturation?II How Does a Smart Watch Measure Blood Oxygen?The blood oxygen measurement function of the smart watch actually judges health by measuring the human arterial blood oxygen saturation. The blood oxygen saturation specifically refers to the percentage of hemoglobin combined with oxygen in the blood, that is, the concentration of blood oxygen in the blood. Generally speaking, if the blood oxygen saturation is below 94%, it will be regarded as insufficient oxygen supply. Many clinical diseases will cause insufficient oxygen supply, which directly affects the normal metabolism of cells, and in severe cases, it can be life-threatening. Therefore, blood oxygen testing is very important for clinical medicine. The most primitive method of tracing blood oxygen measurement requires blood sampling first, and then electrochemical analysis by a blood gas analyzer to obtain the blood oxygen saturation. This method has complicated steps and cannot achieve continuous detection. However, with the development of clinical medicine, non-invasive blood oxygen measurement is now widely used. As long as a finger pressure photoelectric sensor is worn for the patient, continuous blood oxygen detection can be realized. The essence is to use red light with a wavelength of 660nm and near-infrared light with a wavelength of 940nm as the intake light source, measure the light transmission intensity through the tissue bed, calculate the blood oxygen concentration and blood oxygen saturation, and display the results by the instrument. The principle of measuring blood oxygen with a smart watch is similar to acupressure measurement, but the difference is that the part illuminated by the light source of the watch is the wrist, which is not as "transparent" as the finger. Visible light and infrared light cannot penetrate, so it is more challenging. However, as a wearable device with a very high frequency of use, the stimulation brought by the development space of smart watches is far greater than the challenges they need to face.Figure3. How Does a Smart Watch Measure Blood Oxygen?III What is the use of Measuring Blood Oxygen Saturation?Because the blood oxygen saturation can be detected anytime and anywhere through smart wearable devices, the application scenarios of blood oxygen detection are very wide. (1) Assist in judging the state of sleep breathingIntermittent apnea may occur during sleep, which may cause insufficient oxygen supply. Through continuous blood oxygen detection, the blood oxygen saturation data during sleep can be recorded, and the data can be used to analyze whether there is hypoxia during sleep, so as to determine the sleep health status. In addition, like some people who often work overtime, they can also use the blood oxygen saturation detection function to judge the current state. If the blood oxygen saturation is low, you may need to take a quick rest, and that is friendly to your health.Figure4. Judging the State of Sleep Breathing by Blood Oxygen Saturation (2) Monitor the physical state during exerciseThe blood oxygen saturation detection function not only allows you to know your physical condition at any time in your daily life, but also can play a better health support role in some special scenes. For example, in outdoor extreme mountaineering and other sports scenes, you can know your physical condition at any time through blood oxygen saturation, determine whether you need to rest or adjust the exercise intensity, so as to better cope with various sports scenes.Figure5. Monitor the Physical State During Exercise (3) Monitor the health of parentsGenerally, the APP on the mobile phone can synchronize the health data of the smart wearable device, so even if you are away from home, as long as you equip your parents with a smart wearable device, you can learn about your parents’ blood oxygen data and some other health data through remotely synchronized data. , adding more details for your concern.IV Is it Reliable to Measure Blood Oxygen with a Smart Watch?At present, the blood oxygen measurement function on a smart watch has not been certified by NMPA or FDA, that is, it has reached the level of medical diagnosis. The blood oxygen monitoring module of the smart watch consists of three parts: an optical sensor, a front-end signal acquisition system, and an algorithm. The principle is based on the different absorption rates of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) in the blood to red light and infrared light, the red light and infrared light are irradiated to the skin through an optical sensor, and then the blood vessels under the skin are obtained. After the reflection of the red light and infrared light, the blood oxygen is calculated by the algorithm. The optical sensor is the core of the blood oxygen detection module, which is usually composed of several LED lights and diodes. Apple's official website shows that the blood oxygen sensor equipped with Apple Watch 6 consists of four groups of LED light clusters and four photodiodes, and is integrated in the crystal glass back. If a smart watch is required to measure both heart rate and blood oxygen, it can be achieved through the same optical sensor. Ams has launched an optical sensor that integrates blood oxygen measurement and heart rate measurement. Li Minghao, field application engineer manager at ams, said, “Heart rate measurement usually uses green light, and blood oxygen measurement uses red light and infrared light. Compared with optical sensors that can only measure heart rate, optical sensors that can simultaneously perform two functions The composition usually adds several red and infrared LEDs.Figure6. Samsung Galaxy Series Smart WatchAs the core of blood oxygen measurement, the accuracy of optical sensors is very important to the accuracy of measurement results. For example, deviations in the wavelength of the red light produced by the diode may cause inaccurate measurement results. "Smartwatch measuring blood oxygen is a signal obtained by measuring capillaries. The signal is very weak. Usually this signal is submerged on it, and the feedback signal may be only about 1% useful. Therefore, the design of optics and filtering is very important." Li Minghao said.Currently, companies in the industry are taking various measures to improve accuracy. The senior technical staff of Huami Technology said, "Any sensor has various non-ideal errors. In terms of control errors, Huami conducts strict testing and evaluation of all key parameters when selecting optoelectronic devices. Each product of Mi has undergone multiple measurements on the production line to ensure that the accuracy of the factory product parameters is within the design range. In addition, at the beginning of the design, select the relatively flat waveband of the human skin spectral absorption curve to limit the wavelength error to the blood oxygen The impact is within an acceptable range." Increasing the number of sensors is also one of the ways to improve accuracy. The vivo watch is equipped with a self-developed 5-core optical heart rate blood oxygen sensor to achieve blood oxygen measurement. "5-core refers to a multi-sensor system composed of 5 sensors, in which the circuit and optical design are the results of vivo's independent research. Compared with the single sensor or multi-sensor design in the industry, it has a larger signal receiving area and receiving capacity. Stronger, can achieve more accurate monitoring effects." said a senior technical staff of vivo. However, judging from the actual effect of the current smart watch for blood oxygen measurement, although there is an improvement in accuracy, there is still a certain gap between achieving medical-level blood oxygen monitoring. When the news that Apple Watch 6's blood oxygen measurement function was inaccurate, Apple came out to clarify that this function is only for health reference, not as a medical diagnosis standard. The accuracy requirements of consumer and medical products are different. Taking the heart rate as an example, there is no problem with a few beats on the wrist, but in medical treatment, there can only be a difference of 1-2 beats.V Comparison with Pulse Oximeter5.1 What is a Pulse Oximeter?Pulse oximeter has been a common medical device since the 1970s. It is most commonly used for people with respiratory diseases and sometimes for athletes and pilots who must monitor blood oxygen levels. They are mainly used for clinical testing and monitoring, but for certain groups of people, they may also be used at home.Figure7. Pulse Oximeter5.2 How Does a Pulse Oximeter Work?Based on the change in light absorption during arterial pulsation. Two light sources located in the visible red spectrum (660 nanometers) and infrared spectrum (940 nanometers) alternately illuminate the tested area (usually fingertips or earlobes). The amount of light absorbed during these pulses is related to the oxygen content in the blood. The microprocessor calculates the ratio of the two spectra absorbed, and compares the result with the saturation value table stored in the memory to obtain the blood oxygen saturation. A typical oximeter sensor has a pair of LEDs that face a photodiode through a translucent part of the patient's body (usually a fingertip or earlobe). One of the LEDs is red light with a wavelength of 660nm; the other is infrared light with a wavelength of 940nm. The percentage of blood oxygen is calculated by measuring the two wavelengths of light with different absorption rates after passing through the body. 5.3 Main ComponentsA microprocessor, memory (EPROM and RAM), two digital-to-analog converters that control LEDs, a device that filters and amplifies the signal received by the photodiode, and an analog-to-digital converter that digitizes the received signal to provide the microprocessor . The LED and photodiode are placed in a small probe that is in contact with the patient's fingertip or earlobe. Pulse oximeters generally also include small liquid crystal displays. 5.4 Can a Smart Watch Replace a Pulse Oximeter?The answer is no. Fitness bracelets (including some Garmin devices) and smart watches with the function of detecting blood oxygen levels cannot be used as medical equipment. Garmin said that blood oxygen saturation can help you understand your body's adaptation to high altitude (especially for mountain sports and adventure), and it can also be a reminder for symptoms of sleep apnea or overwork during exercise. But it also clearly states that these data cannot be used for medical purposes, nor can it diagnose, treat, cure or prevent any disease or condition. The location where the device is worn may affect accuracy. The fitness tracker is worn on the wrist instead of the fingertips, it is easier to move when worn on the wrist, and the blood concentration on the skin surface is lower than that on the fingertips, so the obtained blood oxygen measurement may have a large error. However, although fitness trackers and smart watches are not medical devices, if they do detect abnormalities and alert you, then you should pay attention.Figure8. Apple WatchVI Is it Necessary to Have an Oximeter at Home During Covid-19?One of the powerful aspects of COVID-19 is that some patients with very low blood oxygen levels do not feel it themselves and are not aware of the severity of their illness. This has led some doctors (especially in the United States) to recommend pulse oximeters at home. Sounds reasonable, doesn't it? However, you must know that although they are commonly used in hospitals, their value for healthy people at home is limited. Equipment problems or incorrect use may cause inaccurate readings, so it is not wise to rely solely on oximeters without comprehensive diagnostic support from medical staff. 6.1 Can a Pulse Oximeter Diagnose Covid-19?The pulse oximeter may indicate a problem with the blood oxygen level, which may be related to the coronavirus, but it is only part of a comprehensive diagnosis. Blood oxygen saturation can help clinical decision-making, but it cannot replace clinical evaluation, nor can it be diagnosed alone. Some doctors suggest that for patients with suspected symptoms of the new crown but not serious enough to be hospitalized, they can consider using a pulse oximeter at home for monitoring.Figure9. Covid Prevention6.2 Is it Necessary to Buy a Pulse Oximeter?If you don’t have any breathing problems and have never used it before, then you don’t need to buy a pulse oximeter. It is usually only used if recommended by a doctor. Professor Xu, a clinical assistant professor at the University of Hong Kong and honorary consultant of respiratory and intensive care medicine at the Royal Free Hospital in London, said that pulse oximeters are still useful as early home self-monitoring equipment. Those who are weak, prone to respiratory failure, suffer from chronic respiratory diseases or need oxygen therapy at home can prepare one. Some people want to buy one for a self-test to find out their "normal" oxygen level, just in case. In fact, if you are not a suspected patient and have no symptoms, there is no need to buy one. Without the help of medical personnel, the measured readings are not very useful, and if you have not used them before, misuse or misinterpretation of the numbers is easy to happen. Dr. Andy Whittamore, the clinical director of the British Asthma Association and the British Lung Foundation, suggested: "Any surveillance at home should be part of the diagnosis, but not a substitute for clinical advice. All people who are concerned about their symptoms should see a doctor. In addition, like many coronavirus-related products, such as masks, due to the promotion of pulse oximeters, demand has also begun to increase, so beware of unscrupulous sellers selling substandard products at high prices.  VII FAQ1. Can a smartwatch measure blood oxygen?Thankfully, tech companies like Apple, Samsung, Realme, and Garmin have been experimenting with Sp02 sensors on their wearables to allow users to monitor not just blood oxygen saturation but other health data, on the go. 2. How do smartwatches measure oxygen levels?Both medical and wearable oximeters use light to do so. Typically, a pulse oximeter features two LEDs with different light wavelengths — one red and one infrared. ... Most recent watches and fitness trackers usually have sensors that provide pulse ox sleep tracking too. 3. How is oxygen level in blood measured?A pulse oximeter measures how much light is absorbed by your blood. This tells us how much oxygen your blood contains. The pulse oximeter shines 2 lights through your fingertip or earlobe: one red light and one infrared light.