What is a sensor? Sensor Basics Understanding fundamental principles and features 01 Photoelectric Sensors 02 Inductive Proximity Sensors 03 Contact Sensors 04 Ultrasonic Sensors
Introduction Sensors have now become crucial to improve productivity. There is a wide variety of sensors, each has its strengths and weaknesses. This document is designed to serve as a textbook to learn the basics of sensors/measuring instruments based on detection principles. Utilise and share this textbook as a resource for all those involved with sensors. 2
Table of Contents Photoelectric sensors P04 Photoelectric Sensors 01 Detection based on light Fibreoptic sensors P08 Laser sensors Received light recognition type Position recognition type P12 P14 Inductive Proximity Sensors 02 Detection based on eddy current Proximity sensors Inductive displacement sensors P16 P20 Contact Sensors 03 Detection based on contact Contact-type displacement sensors P21 Ultrasonic Sensors 04 Detection based on ultrasonic Ultrasonic sensors P25 3
01 Photoelectric Sensors Detection based on light Photoelectric sensors Outline 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 thrubeam type sensor is used to measure the change in light quantity caused by the target crossing the optical axis. Principle and major types A beam of light is emitted from the light emitting element and is received by the light receiving element. Reflective model Both the light emitting and light receiving elements are contained in a single housing. The sensor receives the light reflected from the target. Transmitter/Receiver Light emitting element Light receiving element Reflected light Target Thrubeam model The transmitter and receiver are separated. When the target is between the transmitter and receiver, the light is interrupted. Transmitter Light emitting element Signal light Target Signal light is interrupted. Receiver Light receiving element Retroreflective model Both the light emitting and light receiving elements are contained in same housing. The light from the emitting element hits the reflector and returns to the light receiving element. When a target is present, the light is interrupted. Transmitter/Receiver Light emitting element Light receiving element Target Signal light is interrupted. Reflector 4
01 Photoelectric Sensors Detection based on light Photoelectric sensors Features Non-contact detection Since detection is possible without contact, there will be no damage to targets. The sensor itself will not be damaged either, ensuring long service life and maintenance-free operation. Almost all materials detectable Since the sensor either detects targets based on the reflectivity or the quantity of interrupted light, almost all kinds of materials are detectable. This includes glass, metal, plastic, wood, and liquid. Long detecting distance Photoelectric sensors are generally high power and allow long-range detection. Tip KEYENCE s PZ-G Series has built-in Alignment indicators that are obvious, even from long distances. When the optical axes are aligned, the Alignment indicator illuminates on the receiver. The light can be seen clearly even from a long distance so a single operator can align the sensors easily and quickly. Notification with light 5
01 Photoelectric Sensors Detection based on light Photoelectric sensors Classification Type Detection configuration Features Thrubeam Transmitter Target Receiver Detection occurs when the target crosses the optical axis between transmitter and receiver. Long-detecting distance Stable detecting position Opaque objects detectable regardless of shape, colour or material Powerful beam Retroreflective Transmitter/receiver Target Reflector Detection occurs when the target crosses the optical axis between sensor head and reflector. Reflector allows installation in a limited space Simple wiring Longer detecting distance than the diffuse-reflective sensor type Easily-adjustable optical axis Opaque objects detectable regardless of shape, colour, or material Diffusereflective Transmitter/receiver Target Detection occurs when the light beam, emitted to the target, is reflected by the target and received. Space-saving (requires installation of sensor unit only) Adjustment of optical axis not required Reflective transparent objects detectable Colour differentiation possible Focusedbeam reflective Transmitter/receiver Target Detection occurs when the beam spot, emitted to the target, is reflected by the target and received. Minute objects detectable Target markings detectable Detection possible through narrow openings between machines Visible beam spot Small-spot definite reflective Target Transmitter/receiver The transmitting and receiving portions are constructed at an angle, allowing detection within the limited area where the optical axes intersect. Effect of target background is minimal Low hysteresis Slight height differences are detectable Visible beam spot Fixeddistance Transmitter/receiver Target Detects the target at a specific distance according to the angle of the reflected light beam. Unaffected by highly reflective targets or backgrounds Stable detection of materials with varying reflectance and colour Highly accurate detection of minute objects Visible beam spot Lustre recognition Transmitter/ receiver Target When the light beam hits a target, the beam reflects differently according to the lustre of the target. The sensor detects the difference in lustre based on how the beam reflects (specular or diffusive). On-line detection is possible. Detection is not affected by target colour. Transparent targets can be detected. 6
01 Photoelectric Sensors Detection based on light Photoelectric sensors Other variations There are various types of photoelectric sensors depending on environment or installation location. The following are typical classifications which allow you to select photoelectric sensors more suitable for your environment. Self-contained type Setup and feedback is found on the sensor unit itself. These units are typically a little larger. Classification based on whether the amplifier is separated or not Separate-amplifier type An amplifier is separate from the sensor head to allow for remote setting and feedback. This allows the sensor head to be smaller and more flexible to mount. Plastic housing type The housing is made of plastic. Most models are relatively lightweight; however, their frame strength is inferior to that of the metal housing type. Classification based on housing material Metal housing type The housing is made of metal such as stainless steel. This type is robust and has long service life compared to the plastic housing type. 7
01 Photoelectric Sensors Detection based on light Fibreoptic sensors Outline The fibreoptic sensor has an optical fibre connected to a light source to allow for detection in tight spaces or where a small profile is beneficial. Principle and major types The optical fibre consists of the core and the cladding, which have different refractive indexes. The light beam travels through the core by repeatedly bouncing off the wall of the cladding. The light beam, having passed through the fibre without any loss in light quantity, is dispersed at an angle of approximately 60 and emitted to the target. Optical fibre configuration LED Approx. 60 Core (high refractive index) Cladding (low refractive index) The cores are divided into the following types: Plastic type The core of the plastic-fibre consists of one or more acrylic-resin fibres 0.25 to 1 mm in diameter, encased in a polyethylene sheath. Plastic fibres are light, cost-effective, and flexible which is why they are the most common type of fibre sensor. Glass type The glass-fibre consists of 10 to 100 μm diameter glass fibres encased in stainless steel tubing. This allows it to be used at high operating temperatures (350 C max.). The optical fibre sensors are divided into two categories: thrubeam and reflective. The thrubeam type comprises a transmitter and a receiver. The reflective type, which is a single unit, is available in 3 types: parallel, coaxial, and separate. The 3 are based on the shape of the crosssection of the optical fibre. Type Parallel Coaxial Separate Description Generally used for plastic fibres. High-precision type, consisting of a core (transmitter) and surrounding area (receiver). The operating position can remain the same regardless of the direction from which the target enters the detecting area. This type, containing several 10 μm glass fibres in diameter, has separate areas for the transmitter and receiver. 8
01 Photoelectric Sensors Detection based on light Fibreoptic sensors Features Versatile installation A flexible optical fibre enables easy installation in limited spaces such as a space between machines. Detection of extremely small targets The extremely compact sensor head allows for easy detection of extremely small targets. Excellent environmental resistance Since no electric current flows through the optical fibre cable, the sensor is unaffected by electrical noise. The heat-resistant type fibre unit enables detection in high temperature environments. Tip KEYENCE s FS-N Series of fibreoptic amplifier allows connection of more than 100 types of special fibre units. It has various features to improve stability, such as the automatic maintenance function which automatically compensates for dust and dirt build up. 9
01 Photoelectric Sensors Detection based on light Fibreoptic sensors Classification Fibre units have many variations. Because the fibre does not house any of the electronic components, there are very few limitations on size and shape. The following is a classification example of KEYENCE s fibre units (FU Series). Standard/Simple Mounting Threaded and Hex-shaped Fibres Threaded for easy mounting onto brackets and machine equipment. Cylindrical (Set Screw Installation) Suitable for installation in locations where space is limited. Installed by drilling a hole and using a set screw Integrated bracket The sensor is integrated into an L shaped bracket, which simplifies installation. Small Spot/Focused Beam Small Spot Reflective Great for small object detection. Spot size and focal distance are adjustable, so there is no need to change the distance between the sensor and the target. Focused Beam/High power Use of a lens reduces the field of view based on the aperture angle. This narrow beam helps avoid deflection and is suitable for detecting objects at longer distances. Transparent object detection Retro-reflective Effective for detecting transparent objects. The beam passes through the (transparent) target twice, so light attenuation increases. Definite-reflective Detects within a fixed range. Reduces background effects and features a space saving, thin profile design. Flat Bracket Fibres Sleeve Small space Environment-proof Dedicated application This thin profile sensor comes with mounting holes for installation where space is limited. Oil/Chemical Resistant The fluorocarbon resin coating allows these fibres to be used in almost any environment, including oil or chemical splash conditions. Area The wide area beam is ideal for applications where there is variance in target position and for detecting multiple shapes or moving targets. The thin sleeve design eliminates problems caused by limited mounting space and allows the sensor to be placed closer to the target. Lineup includes side view and bendable sleeve types. High-flex Provides higher flexibility than an electric wire. Resistant to 30 million bends! Liquid-level Accurate liquid level detection sensors are available in transparent tube-mount or immersion type models. Heat Resistant Ideal for use in high temperature applications. Withstands temperatures up to 350 C. Vacuums Can be used in vacuum and high temperature environment. 10
01 Photoelectric Sensors Detection based on light Fibreoptic sensors Key terms for selection The following is the key terms for selecting a fibre unit and their meaning. Fibre unit length The length of a fibre unit. A longer fibre unit can be installed at a location farther from the fibreoptic amplifier. Ambient temperature The range of temperature in which the fibre unit can be used. To use a fibre unit at high ambient temperature, it is recommended to select a heat-resistant type. Bend radius The index indicating the maximum radius in which the fibre unit can be bent and still operate without problems. Fibre units with smaller bend radius are beneficial in locations where routing is difficult. Detecting distance The distance from which the sensor can detect targets. Optical axis diameter This index is mainly used for thrubeam model fibre units. For thrubeam fibre units, this is the size of object that will obstruct the optical axis entirely. Minimum detectable object The size of the smallest target which the fibre unit can detect. 11
01 Photoelectric Sensors Detection based on light Laser sensors: Received light recognition type Outline A laser sensor uses a laser to emit light in a straight line. Its visible beam spot makes alignment and positioning very easy. Since the light beam is focused, the sensor can be installed without worries about stray light. Principle and major types A light beam is emitted from the light emitting element (laser) in the transmitter and is received with the light receiving element in the receiver. Reflective model Transmitter/Receiver Light emitting element Light receiving element Reflected light Target Thrubeam model Transmitter Light emitting element Signal light Target Signal light is interrupted. Receiver Light receiving element Retroreflective model Transmitter/Receiver Light emitting element Target Reflector Light receiving element Signal light is interrupted. 12
01 Photoelectric Sensors Detection based on light Laser sensors: Received light recognition type Features Visible beam spot for easy installation Unlike LED light, a laser travels in a straight line so that the position of the beam spot can be identified quickly. This greatly reduces installation time compared to photoelectric sensors. Long detecting distance The beam spot remains small over a long range, eliminating any concern about the detecting distance. Small beam spot ensuring high accuracy The minimum beam spot of 50 μm (among KEYENCE lineup) allows for reliable detection of small targets. Detection through a narrow space The focused light allows for detection of targets through a narrow space. Tip With KEYENCE sensors, sensitivity can be set easily with a push of a button. Moreover, the full lineup conforms to Class 1 laser requirements, ensuring safe operation (LV-N Series). 13
01 Photoelectric Sensors Detection based on light Laser sensors: Position recognition type Outline This type of sensor detects the position of a target. This is achieved by using a triangulation system or a time measurement system. Principle and major types Triangulation system The change in the distance to the target affects the position of the light concentrated on the CMOS detecting element. This information is used for detecting the target position. [At reference distance] Light receiving element Semiconductor laser Transmitter lens Receiver lens Example of a reflective model CMOS sensor [Shorter distance] [Longer distance] The laser emits a laser beam to the target as shown above. The light reflected off the target is concentrated by the receiver lens and forms an image on the light receiving element. When the distance changes, the concentrated light reflects at a different angle and the position of the image changes accordingly. Time measurement system The distance is measured based on the time in which the emitted laser beam returns to the sensor after hitting the target. The detection is unaffected by the surface condition of the target. Example of a reflective model Time of Flight (TOF) sensor [At reference distance] Distance to the target: Y Laser pulse emission Received light Time before the reflected light is received: T In the figure to the right, the sensor detects the time (T) that is the time until the reflected laser beam is received to calculate the distance (Y). The calculation formula is: 2Y (go-and-return distance) = C (light speed) T (time before the reflected light is received) 14
01 Photoelectric Sensors Detection based on light Laser sensors: Position recognition type Features Not just for presence detection - measurement is also possible Certain models can measure distance and position with higher accuracy than a simple sensor. The following are some examples of KEYENCE products: CCD thrubeam model IG Series A laser is emitted from a transmitter and then is received by a CCD light receiving element. The area where the laser is interrupted is identified clearly on the CCD. This model can be used for in-line position detection or outer diameter measurement of a target. High accuracy CMOS reflective model IL/IA Series Reflected light is received with a CMOS light receiving element and the position is determined based on the triangulation principle. This model can output the position information with an analogue signal. 15
02 Inductive Proximity Sensors Detection based on eddy current Proximity sensors Outline A proximity sensor can detect metal targets approaching the sensor, without physical contact with the target. Proximity sensors are roughly classified into the following three types according to the operating principle: the high-frequency oscillation type using electromagnetic induction, the magnetic type using a magnet, and the capacitance type using the change in capacitance. Principle and major types General sensor A high-frequency magnetic field is generated by coil L in the oscillation circuit. When a target approaches the magnetic field, an induction current (eddy current) flows in the target due to electromagnetic induction. As the target approaches the sensor, the induction current flow increases, which causes the load on the oscillation circuit to increase. Then, oscillation attenuates or stops. The sensor detects this change in the oscillation status with the amplitude detecting circuit, and outputs a detection signal. Target (Metal) High-frequency magnetic field Sensing coil Internal circuit Nonferrousmetal type [Metal object absent] [Aluminium object absent] The nonferrous-metal type is included in the high-frequency oscillation type. The nonferrous-metal type incorporates an oscillation circuit in which energy loss caused by the induction current flowing in the target affects the change of the oscillation frequency. When a nonferrous-metal target such as aluminium or copper approaches the sensor, the oscillation frequency increases. On the other hand, when a ferrous-metal target such as iron approaches the sensor, the oscillation frequency decreases. When the oscillation frequency becomes higher than the reference frequency, the sensor outputs a detection signal. Magnetic objects and non-magnetic objects Remember that magnetic objects are easily attracted by a magnet, whereas non-magnetic objects are not. [Metal object present] [Aluminium object present] Magnetism Strong Weak Detecting distance of general-purpose model Detecting distance of aluminium detection model Long Short Short Long Typical metal Iron/SUS440 SUS304* Aluminium/brass/copper * SUS304 has an intermediate property. 16
02 Inductive Proximity Sensors Detection based on eddy current Proximity sensors Features Detecting metal only Inductive proximity sensors can only detect metal targets. They do not detect non-metal targets such as plastic, wood, paper, and ceramic. Unlike photoelectric sensors, this allows a proximity sensor to detect a metal object through opaque plastic. ON!! Plastic Metal Excellent environmental resistance Proximity sensors are durable. For example, all KEYENCE sensor head models satisfy the IP67 requirements by sealing the inside with filling material or other measures. Since these sensors only detect metal objects, the detection is not affected by accumulated dust or oil splash on the sensor head. Tip Two-wire type proximity sensors allow simplified wiring and can be used for both NPN and PNP circuits. Another advantage is that their current consumption is extremely low such as 1 ma (EV Series). 17
02 Inductive Proximity Sensors Detection based on eddy current Proximity sensors Classification General-purpose model Type Self-contained Amplifier-in-cable Separate-amplifier Model EV, EZ EM ES Sensitivity adjustment Not possible Not possible Possible Sensor head size Large Small Accuracy Low High Aluminium detection model Type Model Iron detection Sensitivity adjustment Self-contained ED Possible (See the characteristic diagram for details.) Not possible Classification 1 Self-contained type (EV, EZ, ED) Oscillation circuit Detection circuit Output circuit The sensor can be used as soon as the power is turned on. (Simplified wiring) Sensitivity adjustment not possible Sensing coil Separate-amplifier type (ES) Sensor head Sensing coil Coaxial cable Amplifier unit Oscillation circuit Detection circuit Output circuit Small sensor head (Wiring is required between the sensor head and amplifier.) Longer detecting distance compared with the self-contained type Fine adjustment is possible with a sensitivity adjustment trimmer, which enables high accuracy detection. Amplifier-in-cable type (EM) Sensor head Amplifier unit Oscillation circuit Detection circuit Output circuit The sensor can be used as soon as the power is turned on. (Simplified wiring) Small sensor head and amplifier Sensitivity adjustment not possible Sensing coil Coaxial cable 18
02 Inductive Proximity Sensors Detection based on eddy current Proximity sensors Classification Classification 2 Shielded type Flush mounting The side of the sensing coil is covered with metal shielding. This type can be used by being embedded in metal. (Excluding the EM Series) Non-shielded type The side of the sensing coil is not covered with metal shielding. This type offers a longer detecting distance compared with the shielded type. Since the sensor is easily affected by surrounding metal objects, attention is required for the mounting position. Countersinking required øa B 19
02 Inductive Proximity Sensors Detection based on eddy current Inductive displacement sensors Inductive displacement sensors not only detect the presence of a target but also measure the distance to a target. (1) EX-V, EX-200 and AS Series As the target approaches the sensor head, the eddy current loss increases and oscillation amplitude becomes smaller accordingly. This oscillation amplitude is rectified to obtain DC voltage variations. Target (Metal) Target Far Near Far Oscillation amplitude Far Near Rectified signal Sensor head 0 V The rectified signal and distance have an approximate proportional relationship. The linearisation circuit corrects the linearity to obtain a linear output that is proportional to the distance. Analogue voltage output 100% Output voltage 100% Linearisation Final output Output voltage 0 Measuring distance 0 Measuring distance (2) EX-500 Series (All metal type) As a target approaches the sensor head, the oscillation amplitude becomes smaller and the phase difference from the reference waveform becomes larger. By detecting changes in the amplitude and phase, the sensor can obtain a value approximately proportional to the distance. Then, a high-accuracy linearisation processing corrects the value digitally based on the target material, to obtain a linear output that is proportional to the distance. Distance: Far Amplitude: Large Phase difference: Small Distance: Middle Amplitude: Middle Phase difference: Middle Reference waveform Distance: Near Amplitude: Small Phase difference: Large The EX-500 Series detects both amplitude and phase difference to enable detection of nonferrous metals such as copper and aluminium so that it can be an all metal supporting sensor. When only the magnitude of the amplitude is detected, it is hard to determine whether it is changing due to the change in the material or due to the distance to the target. Therefore, the sensor detects the change in the phase as well to verify the change in the material. 20
03 Contact Sensors Detection based on contact Contact displacement sensors Outline As the name indicates, this is a sensor measuring the position of a target by directly contacting it. When the height of the spindle changes as shown in the figure on the right, the sensor internally calculates the amount of displacement. Contact displacement sensors are mainly used for detecting the height, thickness, or warpage of the target. Spindle Contact [Air push type measuring by extending a spindle] Since measurement is possible with the sensor head being fixed, no mechanism is required to move the sensor head. This saves installation space and greatly reduces man-hours during installation. Standard model Linear guide Slotted jig Stopper Since the sensor can be fixed at the same position, no complicated jig is required. There is also no errors due to the influence of a jig on accuracy. GT2 Air push type No jigs required Features The following table shows typical characteristics that vary depending on the detection system. [Sensor type comparison based on the detection method] Item Inductive Optical Ultrasonic Laser focus Contact Detectable target Metal Almost all materials Almost all materials Almost all materials Solid Measuring distance Short Normal Long Short Short Accuracy High High Low High High Response speed Fast Fast Slow Normal Slow Dust, water, oil, etc. Unaffected Normal Normal Normal Unaffected Measuring surface Normal Small Large Small Small 21
03 Contact Sensors Detection based on contact Contact displacement sensors Principle and major types Contact-type displacement sensors are generally divided into the following two groups depending on the detection method: Differential transformer method -> Method using a magnetic coil Scale method -> Method using an internal scale (ruler). In addition, there is another method originally developed by KEYENCE: Scale Shot System -> World s first method in which a CMOS sensor records a unique pattern on an absolute value glass scale. Differential transformer method The sensor using the differential transformer method has an internal coil that generates a magnetic field when a current flows. When a core is inserted into it, the impedance of the coil changes according to the distance the core is inserted, resulting in the change in the signal level. The sensor detects this change in signal level and converts it into travel range. Structure of the GT Series Coil Core Spring When the cylinder extends Correction coil Sensing coil Core When the cylinder retracts Linear ball bearing Dust boot Signal level Signal level Contact Advantage The absolute position can be obtained based on the signal level that changes in accordance with the spindle position. (No zero point adjustment necessary, no tracking errors) Disadvantage The accuracy decreases at the end of the spindle. Since the system is coil-based, the magnetic field is applied evenly around the centre but is not consistent near the end. Consideration should be given to the linearity and temperature characteristic, as they can alter results. 22
03 Contact Sensors Detection based on contact Contact displacement sensors Principle and major types Scale method Advantage High accuracy (The accuracy basically depends on the resolution of the scale markings.) No need to consider the linearity because the scale markings are consistent along the entire scale. The temperature characteristics are good because the scale markings do not change with varying temperature. Disadvantage When the spindle moves abruptly due to vibration or other reason, the response of the photoelectric sensor may delay, resulting in tracking errors. 23
03 Contact Sensors Detection based on contact Contact displacement sensors Principle and major types Scale Shot System (KEYENCE original principle) Like typical scale method sensors, KEYENCE s GT2 Series includes a transmitter, a receiver, and a scale within the unit. However, its slits are not simple ones used by typical scale method sensors. The scale of the GT2 Series uses slits with complex and unique patterns. The sensor can read this pattern to identify the spindle position. (1) When the spindle moves, the absolute value scale moves accordingly. (2) The CMOS sensor reads the complex pattern in the scale at high speed. (3) The spindle position information is sent to the amplifier. Scale Shot System World s first, high-speed scale shot system using a CMOS sensor that absorbs light passing through an absolute value glass scale, which displays different patterns depending on the position. Prism incorporated to form parallel light. LED parallel light Free from deformation Quarts glass scale Easy mounting/ replacement Detachable cable Absolute value scale Transmitter Advantages of the conventional scale (pulse count) method High accuracy along the entire measuring range Good temperature characteristics Advantages of the conventional differential transformer method No tracking errors Absolute position detection Approx. 6 µs shutter speed CMOS sensor CMOS sensor * Shutter speed: Approx. 6 µs, Shooting interval: 1 ms Advantage Disadvantage Absolute position detection Since the sensor detects position information, it does not require zero point adjustment and not produce tracking errors. The scale method ensures high accuracy in the entire measuring range. Good temperature characteristics Nothing in particular 24
04 Ultrasonic Sensors Detection based on ultrasonic Ultrasonic sensors Outline and detection principle As the name indicates, ultrasonic sensors measure distance by using ultrasonic waves. The sensor head emits an ultrasonic wave and receives the wave reflected back from the target. Ultrasonic sensors measure the distance to the target by measuring the time between the emission and reception. Distance: L An optical sensor has a transmitter and receiver, whereas an ultrasonic sensor uses a single ultrasonic element for both emission and reception. In a reflective model ultrasonic sensor, a single oscillator emits and receives ultrasonic waves alternately. This enables miniaturisation of the sensor head. [Distance calculation] The distance can be calculated with the following formula: Distance L = 1/2 T C where L is the distance, T is the time between the emission and reception, and C is the sonic speed. (The value is multiplied by 1/2 because T is the time for go-and-return distance.) Features The following list shows typical characteristics enabled by the detection system. [Transparent object detectable] Since ultrasonic waves can reflect off a glass or liquid surface and return to the sensor head, even transparent targets can be detected. [Resistant to mist and dirt] Detection is not affected by accumulation of dust or dirt. [Complex shaped objects detectable] Presence detection is stable even for targets such as mesh trays or springs. 25
04 Ultrasonic Sensors Detection based on ultrasonic Ultrasonic sensors Outline and detection principle Comparison between optical sensors (reflective model) and ultrasonic sensors Typical sensors used for distance measurement are optical sensors. The following table shows the advantages and disadvantages when optical sensors and ultrasonic sensors are compared. Note that this table is based on KEYENCE products. Item Optical (reflective model) * Ultrasonic Detectable target Detection is affected by target materials/colours Detection is unaffected by target materials/colours Detecting distance 1000 mm max. 10 m max. Accuracy High Low Response speed Fast Slow Dust/water Affected Unaffected Measuring range Small Large * Excluding the Time of Flight (TOF) type Note What is ultrasonic? Ultrasonic generally refers to a high pitch sound that is inaudible to humans. Sound is expressed by a unit called frequency (Hz). The greater the frequency, the higher the pitch of sound becomes. The unit Hz (hertz) means the number of oscillations per second. For example, a wave that oscillates 100 times in a second is expressed as 100 Hz. The audible range for humans is said to be between about 20 Hz and 20 khz. In other words, ultrasonic waves have a frequency of 20 khz or greater. Familiar examples of devices using ultrasonic waves In our ordinary life, the following ultrasonic sensors are used: Fish detector (used for fishery or bass fishing) Active sonar in a submarine (used for finding enemy submarines or battle ships) Back sonar for cars (for detecting obstacles during backing a car to prevent single-car accident) 26
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