Thermocouples, They are widely used in industrial systems

They are widely used in industrial systems, HVAC, automobiles, medical devices, and IoT applications to monitor and control temperature.

1. SMART SENSORS by Mr. G. Sattibabu Assistant Professor Department of Electronics and Communication Engineering Aditya College of Engineering & Technology Aditya College of Engineering & Technology UNIT - III

2. UNIT III: Smart Sensor (JNTUK R19 syllabus)   Occupancy and Motion Detectors: Ultrasonic, Microwave Motion, Capacitive Occupancy, Visible and Near-Infrared Light, Far-Infrared Motion, PIR Motion, Position, Displacement, and Level Sensors: Potentiometric, Gravitational, Capacitive, Inductive and Magnetic, Optical, Ultrasonic, Radar   Velocity and Acceleration Sensors: Capacitive Accelerometers, Piezoresistive Accelerometers, Piezoelectric Accelerometers, Thermal Accelerometers, Heated-Plate Accelerometer, Heated- Gas Accelerometer, Gyroscopes, Piezoelectric Cables   Applications: Case studies in manufacturing industries, robotics 01-09-2022 2

3. 01-09-2022 3 Part I: Occupancy and Motion Sensor/detectors

4. 01-09-2022 4 Occupancy sensor and motion sensor The Occupancy sensor detects presence of people or animals in the target monitored area. The motion sensor responds to moving objects only. The difference between them is occupancy sensor produce signals whenever an object is stationary or not while motion sensor is sensitive to only moving objects . These types of sensors utilize some kind of a human body's property or body's actions. For instance, a sensor may be sensitive to body weight, heat, sounds, dielectric constant and so on. The sensors use  infrared ,  ultrasonic ,  microwave , or other technology.

5. 01-09-2022 5 Occupancy sensor and motion sensor Working and Principles: All of the techniques below are used in the design and development of occupancy sensor or motion sensor. These are the basic principles in the design of such sensors. Occupancy sensors are one kind of devices used for detecting whenever space is empty then it is automatically deactivated the light so that the energy can be conserved . This sensor may also activate the lights. This device can also activate the lights routinely by detecting the occurrence of people and provides security and convenience help. Based on the laboratory like Lawrence Berkeley National, the strategies based on occupancy can generate 24% of normal savings of lighting energy. Because of their energy conservation and relative simplicity, these are united with energy code permissions. These sensors are used in the latest construction and also it has a general control feature used in retrofit projects.

6. 01-09-2022 6 Occupancy sensor and motion sensor Basic PIR (passive infrared) sensors detect movement and changes in their field of view. These sensors are simple, providing basic occupied or un-occupied data. A common example of a PIR sensor is a desk sensor that is typically placed on the underside of a desk and is used to detect and report desk occupancy. Ultrasonic sensors emit high-frequency sound waves, outside of human hearing range, and use the doppler effect of returning sounds waves to detect people. Sensors which detect changes in the air pressure due to opening of the doors and also windows are referred as air pressure sensors. The sensors which detect human body capacitance are referred as Capacitive Sensors. Acoustic sensors utilize the sound produced by the people. Photoelectric sensor works on the principle of interruption of light beams by the moving objects

7. 01-09-2022 7 Occupancy sensor and motion sensor Optoelectrical sensor uses detection of variations in the illumination. It also uses optical contrast in the region under target. Pressure mat switches use the pressure sensitive long strips laid on the floors below the carpets to detect weight of an intruder. Stress detectors use strain gauges imbedded into floor beams , staircases , and other structural components Switch sensors utilizes electrical contacts connected to doors and windows. Magnetic switches use a non-contact version of switch sensors. Vibration detectors react to the vibration of walls or other building structures, also may be attached to doors or windows to detect movements. Glass breakage detectors are sensors reacting to specific vibrations produced by shattered glass. Infrared motion detectors are devices sensitive to heat waves emanated from warm or cold moving objects.

8. 01-09-2022 8 Occupancy sensor and motion sensor Microwave detectors are active sensors responsive to microwave electromagnetic signals reflected from objects. Video motion detectors are video equipment which compares a stationary image stored in memory with the current image from the protected area. Video face recognition system uses image analysers that compare facial features with a database. Laser system detectors are similar to photoelectric detectors, except that they use narrow light beams and combinations of reflectors. Triboelectric detectors are sensors capable of detecting static electric charges carried by moving objects

9. 01-09-2022 9 Ultrasonic Sensor: How does a bat locate its prey in the dark? Bats use a process called “echolocation” to locate prey or other objects Ultrasonic Sensor

10. 01-09-2022 10 Ultrasonic Sensor: An ultrasonic sensor is an electronic device that measures the distance of a target object by emitting ultrasonic sound waves , and converts the reflected sound into an electrical signal. Ultrasonic waves travel faster than the speed of audible sound (i.e. the sound that humans can hear). Ultrasonic sensors have two main components: the transmitter (which emits the sound using piezoelectric crystals) and the receiver (which encounters the sound after it has travelled to and from the target).

11. 11 How Can We Measure Distance? Bats use the same principle! In order to calculate the distance between the sensor and the object, the sensor measures the time it takes between the emission of the sound by the transmitter to its contact with the receiver. The formula for this calculation is D = ½ T x C (where D is the distance, T is the time, and C is the speed of sound ~ 343 meters/second). For example, if a scientist set up an ultrasonic sensor aimed at a box and it took 0.025 seconds for the sound to bounce back, the distance between the ultrasonic sensor and the box would be: D = 0.5 x 0.025 x 343 or about 4.2875 meters. 01-09-2022

12. 01-09-2022 12 Microwave sensor What is a Microwave Motion Sensor? A microwave motion sensor uses electro-magnetic radiation . It emits waves which are then reflected back to the receiver. The receiver analyzes the waves that are bounced back. If there is an object moving in the room, these waves are going to be altered. The microwave detector is able to identify changes from moment to moment. Ideally, the receiver should be receiving the same waves back again and again. Because of the way that microwave motion sensors work, they can be either more sensitive or less sensitive. They can identify very minute changes (a totally empty house) or be calibrated to require larger scale movement to avoid false positives .

13. 01-09-2022 13 Microwave sensor What are the Capabilities of a Microwave Motion Sensor? Microwave sensors that are more advanced can also detect whether an individual is moving towards or away from the sensor or moving randomly. These detectors are helpful in sensing and differentiating between the ordinary movement and intruder movement . This feature of these  sensors makes them highly reliable . Microwave sensors are completely safe to use. They can be employed both inside and outside a property and be placed across relatively large areas. They can also be configured to detect different types of activity, such as ignoring certain areas of the home, perhaps where pets or children might be active.

14. 01-09-2022 14 Microwave sensor Benefits of a Microwave Motion Sensor Microwave motion detectors can be used in virtually any environment , including those that are not otherwise hospitable to sensors, such as high heat environments that can set off photo-electric sensors. This makes them one of the most versatile types of sensor system . Microwave detectors can go through walls and holes . This means they can cover a larger area of a home or commercial property, including fairly large outdoor areas. Because of this, they’re usually good for those who need to secure large areas of land. These detectors can also be programmed to reduce the amount of false alarms without having to minimize the of correct positives, therefore improving accuracy and ease of use. Additionally, microwave detectors are generally less expensive to purchase, even though they may be more expensive to run. When shopping for sensors, it’s important to remember the everyday instances that could trigger a false alarm, such as moving drapery or shifting sun patterns. Plus, the sensors require a continuous power draw, so they may be expensive to run. They also only work at intervals rather than working continuously, by sending out signals and then receiving them.

15. 01-09-2022 15 Microwave sensor Active Microwave Sensors: The active sensors usually transmit radio signals toward a target, which spots the signal’s backscattered portion. Also, the sensor measures the strength of the backscattered signal by differentiating between the targets and the time delay between the signals Passive Microwave Sensors: Passive sensors have a long wavelength with small energy radiated from a body. Plus, the atmosphere can easily release them. Hence, they are characterized by low spatial resolution. Also, they are useful for applications like; Measuring atmospheric profiles Determining ozone content

16. 01-09-2022 16 Microwave sensor Non-imaging Radar Non-imaging radars are profiling devices that measure in one linear direction. Interestingly, these sensors include scatterometers and altimeters. Thus, the radar altimeters send out short microwave pulses. Plus, it measures the distance from sensors by gauging the round-trip time delay to targets. Indeed, the scatterometers are useful for making exact measurements (quantitative) of backscattered energy from targets. Interestingly, scatterometry measurements can estimate wind speeds over ocean surfaces. Also, it can measure the backscatter energy on land from various targets of different surfaces and materials. Imaging Radar Unlike non-imaging radar, imaging radar records the intensity of the signal reflection. It also maps signal reflection in a two-dimensional image. Also, the radar images have many dots that represent the backscatter for a specific area.

17. 01-09-2022 17 Microwave sensor Advantages Microwave sensors can cut substantial amount of energy wastage by turning off lights automatically when area is unoccupied. This saves 40% of electricity expenditure of the companies. Moreover, microwave sensors enable auto-dimming of lights which further optimizing the energy charts. They are very sensitive and hence slightest movements are also being detected by them. They have wide coverage range which is about 120 meters. They can detect any motion even beyond the walls or behind the doors . They have benefits of high interference immunity , high precision and high reliability . They require one time servicing to provide lifespan operation. They can be used in harsh environments where heat cycles are irregular. Microwave sensors have wide variety of applications. They are used to monitor functions of bucket elevators and belt conveyors .

18. 01-09-2022 18 Microwave sensor Disadvantages Prone to false alarms due to blowing of objects due to wind, emission from fluorescent lights, penetration through walls etc. For example, when they are used for lighting control in small offices, the sensors switch ON lights even when someone is outside the office premises as they can penetrate walls or glass. They have higher sensitivity and hence they can detect non-human presence such as animals, fast moving objects in the air etc. Microwave frequency do not penetrate metal objects and hence microwave sensors can not reach beyond any metal obstruction. Microwave radiation is hazardous for health and hence low power microwave sensors are preferred. They operate at irregular intervals and hence intruders sometimes are left unnoticed. They are slightly costlier compare to PIR sensors. They consume more energy compare to PIR sensors.

19. 01-09-2022 19 Microwave sensor Microwave Sensor Applications The microwave sensors have a reliable performance in the following applications: Reverse car alarms Speed measure of vehicles Automated doors Respiratory monitors Liquid level measurement Home security systems They are also used for crane proximity detection. City municipalities also use them to monitor waste water and sewage levels. Microwave sensors are used in medical applications such as breast cancer treatment, separation of red blood cells from white blood cells, liver tissue disease detection etc.

20. 01-09-2022 20 Capacitive Occupancy Sensor Figure depicts basic circuit, capacitance between the test plate and earth is equal to value C1. In the time when any person moves in the vicinity of the plate, it builds two additional capacitors ; One between plate and body (Ca) and the other capacitor between body and earth ( Cb ). Hence the resulting total capacitor between plate and earth will become larger by ΔC. C = C1 + ΔC This type of sensor is referred as capacitive occupancy sensor. Being a conductive medium with a high dielectric constant, a human body develops a coupling capacitance to its surroundings.

21. 01-09-2022 21 Capacitive Occupancy Sensor These capacitances Ca and Cb greatly depends on factors such as human body size, their clothing, carrying materials, type of surrounding objects, weather etc. The coupling capacitance will change due to movement of the persons in the target area. This will help the system discriminates static objects compare to the moving objects. Here all the objects form some degree of a capacitive coupling with respect to one another.

22. 01-09-2022 22 Optoelectronic Motion Sensor The most popular intrusion sensors are the optoelectronic motion sensors. This type of motion sensor relies on EM radiation in the optical range. This Electromagnetic radiation will have wavelengths range from 0.4 to 20 µm. The sensor will have distance ranges upto hundred meters and used to find movement of people and animals. Principle: The operating principle of the optical motion detectors is based on the detection of light (either in the visible or nonvisible spectrum) radiated from the surface of a moving object into the surrounding empty region. This radiation may be originated either by an external light source and later got reflected by some object or it may be produced by the object itself in the form of natural emission. The former sensor is referred as an active detector and the later one as a passive detector.

23. 01-09-2022 23 Optoelectronic Motion Sensor As mentioned, an active sensor requires an additional light source such as daylight, electric lamp an infrared LED etc. The passive detectors perceive mid and far infrared emission from objects having temperatures that are different from the surroundings region. Both of these types of detectors use an optical contrast as a means of object recognition and detection .

24. 01-09-2022 24 Optoelectronic Motion Sensor Advantages: The optoelectronic motion sensors are very useful for indicating whether an object is moving or stationary. The most important advantages of an optoelectronic motion sensor are simplicity and low cost. Disadvantages: But they cannot distinguish one moving object from the another. They cannot be utilized to accurately measure the distance to a moving object or its velocity.   The major application areas for the optoelectronic motion sensors are : security systems, energy management etc. In the energy management it is used to switch light on and off. It is also used for making "smart homes", in which we can control various appliances such as air conditioners, cooling fans, stereo players and so on. This is also referred as home automation.

25. 01-09-2022 25 Visible and Near-Infrared Light Sensor A  L i g h t Sensor  generates an output signal indicating the intensity of light by measuring the radiant energy that exists in a very narrow range of frequencies basically called “light”, and which ranges in frequency from “ Infra-red ” to “ Visible ” up to “ Ultraviolet ” light spectrum. ISO  20473 specifies the following scheme: Designation Abbreviation Wavelength Near-Infrared NIR 0.78–3  μm Mid-Infrared MIR 3–50  μm Far-Infrared FIR 50–1,000  μm

26. 01-09-2022 26 Visible and Near-Infrared Light Sensor Principle of Light Sensor: The working principle of the light sensor is based on internal photoelectric effect , which states that when light energy or photons are bombarded on a metal surface than it can cause the free electrons from the metal to excite and jump out resulting in electron flow or electric current. The amount of current produced depends on the energy of the photon (i.e. wavelength of light). The emission of electrons from the metal surface occurs only after the light reaches a certain threshold frequency that corresponds with the minimum energy required by the electrons to break the metal bonds. Light sensors are more commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons).

27. 01-09-2022 27 Visible and Near-Infrared Light Sensor Infrared Sensors works on three fundamental Physics laws: Planck’s Radiation Law : Any object whose temperature is not equal to absolute Zero (0 Kelvin) emits radiation. Stephan Boltzmann Law : The total energy emitted at all wavelengths by a black body is related to the absolute temperature. Wein’s Displacement Law:  Objects of different temperature emit spectra that peak at different wavelengths that is inversely proportional to Temperature.

28. 01-09-2022 28 Visible and Near-Infrared Light Sensor Components of IR Sensor IR Transmitter: IR Transmitter acts as source for IR radiation. According to Plank’s Radiation Law, every object is a source of IR radiation at temp T above 0 Kelvin. In most cases black body radiators, tungsten lamps, silicon carbide, infrared lasers, LEDs of infrared wavelength are used as sources. Transmission Medium: As the name suggests, Transmission Medium provides passage for the radiation to reach from IR Transmitter to IR Receiver. Vacuum, atmosphere and optical fibers are used as medium. IR receiver: Generally, IR receivers are photo diode and photo transistors. They are capable of detecting infrared radiation. Hence IR receiver is also called as IR detector. Variety of receivers are available based on wavelength, voltage and package.

29. 01-09-2022 29 Visible and Near-Infrared Light Sensor Working of IR Sensor An Infrared Sensor works in the following sequence: IR source (transmitter) is used to emit radiation of required wavelength. This radiation reaches the object and is reflected back. The reflected radiation is detected by the IR receiver. The IR Receiver detected radiation is then further processed based on its intensity. Generally, IR Receiver output is small and amplifiers are used to amplify the detected signal.

30. 01-09-2022 30 Applications Consumer electronics: Ever wonder what’s behind your smartphone and tablets that allow for auto screen brightness adjustments? Yes, it’s an ambient light sensor! It measures the ambient light level of your surroundings and determines the suitable brightness of your screen! Automobiles: Similarly, it is used in automobiles to support the drivers’ field of vision. The present light sensor detects surrounding ambient light, and if it’s getting too dark, it’ll automatically turn on light systems! Agricultural Usages: We all know crops need mainly two things for growth; Sunlight and water. This is where a light sensor comes to play, helping farmers keep their crops hydrated yet not over-hydrating it. Here’s how: 1) A light sensor is connected to a sprinkler system, detecting levels of sunlight and only activating it when the sun isn’t at its brightest. 2) It is used alongside other temperature sensors to help gather informative data as well Security applications: Commonly used in circuits for shipment cargos, light sensors are connected to circuits and placed inside as it can detect whenever a container is open due to the change in light exposure. This helps in better processing of lost goods and tracking of personnel. Visible and Near-Infrared Light Sensor

31. 01-09-2022 31 Visible and Near-Infrared Light Sensor Types of Infrared Sensor IR sensors can be classified in two types based on presence of IR source: Active Infrared Sensor Passive Infrared Sensor   Active Infrared Sensor Active Infrared Sensor contains both transmitter and receiver. Most of the cases LED or laser diode is used as source. LED for non-imaging IR sensor and laser diode for imaging IR sensor are used. Active IR Sensor works by radiating energy, received and detected by detector and further processed by signal processor in order to fetch information required. Examples of Active IR Sensor : Break Beam Sensor, Reflectance Sensor. Passive Infrared Sensor Passive Infrared Sensor contains detectors alone. There won’t be a transmitter component. These types of sensors use object as IR source/ transmitter. Object radiates energy and it is detected by IR receivers. A Signal processor is then used to interpret the signal to fetch information required. Example of Passive IR Sensor : Thermocouple-Thermopile, Bolometer, Pyro-Electric Detector, etc.

32. 01-09-2022 32 The PIR Sensor PIR sensor generates energy when exposed to heat. Human or animal body radiates energy in the form of infrared radiation. Hence when human/animal come in the range of PIR motion sensor, it receives thermal energy and hence motion is detected by the sensor. The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can 'see' out past some distance (basically the sensitivity of the sensor). When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a  positive differential  change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected. PIR sensor is used as occupancy sensor. PIR sensor is passive sensor as it senses infrared signal emitted by various objects including human body. They are used as alternative to  microwave sensors .

33. 01-09-2022 33 The PIR Sensor The PIR Sensor Construction The IR sensor itself is housed in a hermetically sealed metal can to improve noise/temperature/humidity immunity. There is a window made of IR-transmissive material (typically coated silicon since that is very easy to come by) that protects the sensing element. Behind the window are the two balanced sensors. Advantages of PIR sensor Detects motion reliably in indoors as well as in day or dark. It consumes less energy (0.8W to 1.0W) compare to microwave sensor. They are cheaper compare to microwave sensors. They are good for electrical applications used in smaller and compact premises

34. 01-09-2022 34 The PIR Sensor Disadvantages of PIR sensor They have lower sensitivity and less coverage compare to microwave sensors. It does not operate greater than 35-degree C. It works effectively in LOS (Line of Sight) and will have problems in the corner regions. It is insensitive to very slow motion of the objects. Since PIR sensors sense heat signatures in room, they are not very sensitive if the room itself is warm . Hence PIR sensors are not able to detect human beings in the summer in some countries like INDIA. Snoozing is another problem with PIR sensors. PIR sensors may turn off even if there is very little movement in occupied floors. Thieves may find it easy to fool PIR detection range as they have slotted detection zone and not continuous one like microwave sensor.

35. 01-09-2022 35 Part II: Position, Displacement, and Level Sensors The measurement of position, displacement or level is very essential for many vivid applications such as process feedback control, transportation traffic control, robotics, security systems and more. Position Sensor: A position sensor is a sensor that detects an object's position. The term position refers to determination of object's co-ordinates (either linear or angular) with respect to a selected reference. Displacement Sensor: A Displacement sensor is a device that measures the distance between the sensor and an object by detecting the amount of displacement through a variety of elements and converting it into a distance. The term displacement refers to moving from one position to another position for a specific distance or angle. Level Sensors: A level sensor is a device that is designed to monitor, maintain, and measure liquid (and sometimes solid) levels.

36. 01-09-2022 36 Potentiometric Sensor Potentiometric Position Sensor: The most commonly used of all the “Position Sensors”, is the potentiometer because it is an inexpensive and easy to use position sensor. It uses a wiper contact linked to a mechanical shaft that can be either angular (rotational) or linear (slider type) in its movement along a track. This movement causes the resistance value between the wiper/slider and the two end connections to change giving an electrical signal output that has a proportional relationship between the actual wiper position on the resistive track and its resistance value. In other words, resistance is proportional to physical position.

37. 01-09-2022 37 Potentiometric Sensor Potentiometer Construction Potentiometers come in a wide range of designs and sizes such as the commonly available round rotational type or the longer and flat linear slider types. When used as a position sensor the moveable object is connected directly to the rotational shaft or slider of the potentiometer. A DC reference voltage is applied across the two outer fixed connections forming the resistive element. The output voltage signal is taken from the wiper terminal of the sliding contact as shown below. This configuration produces a potential or voltage divider type circuit output which is proportional to the shaft position.

38. 01-09-2022 38 Potentiometric Sensor Potentiometer Construction The output signal ( V out ) from the potentiometer is taken from the centre wiper connection as it moves along the resistive track, and is proportional to the angular position of the shaft. Example of a simple Positional Sensing Circuit

39. 01-09-2022 39 Potentiometric Sensor Advantages: Low cost, Low tech, easy to use Disadvantages: wear due to moving parts, low accuracy , low repeatability , and limited frequency response. But there is one main disadvantage of using the potentiometer as a positional sensor. The range of movement of its wiper or slider (and hence the output signal obtained) is limited to the physical size of the potentiometer being used. Most types of potentiometers use carbon film for their resistive track, but these types are electrically noisy (the crackle on a radio volume control), and also have a short mechanical life. Wire-wound pots also known as rheostats, in the form of either a straight wire or wound coil resistive wire can also be used, but wire wound pots suffer from resolution problems as their wiper jumps from one wire segment to the next producing a logarithmic (LOG) output resulting in errors in the output signal. These too suffer from electrical noise. Applications: for this type of high accuracy position sensor is in computer game joysticks, steering wheels, industrial and robot applications.  

40. 01-09-2022 40 Potentiometric Sensor Potentiometer displacement sensors Potentiometer displacement sensor is a primary sensor which converts the linear motion or the angular motion of a shaft into changes in resistance. It is a type of resistive displacement sensor. Linear potentiometers are sensors that produce a resistance output proportional to the linear displacement or position. Linear potentiometers are essentially variable resistors whose resistance is varied by the movement of a slide over a resistance element. Rotary potentiometer are sensors that produce resistance output proportional to the angular displacement or position. They can be either wire wound or conductive plastic, and either rectangular or cylindrical.

41. 01-09-2022 41 Potentiometric Sensor Potentiometer displacement sensors Principles and working The Figure illustrates the basic principle of a linear potentiometer. The linear potentiometer employs an electrically conductive linear slide member (also called wiper) connected to a variable wire wound resistor (winding) that changes resistance to be equated to the linear position of the device that is monitored. As the sliding contact moves along the winding, the resistance changes in linear relationship with the distance from one end of the potentiometer. To measure displacement, a potentiometer is typically wired as a ‘voltage divider’ so that the output voltage is proportional to the distance travelled by the wiper. A known voltage is applied to the resistor ends. The contact is attached to the moving object of interest. The output voltage at the contact is proportional to the displacement. The resolution is defined by the number of turns per unit distance, and loading effects of the voltage divider circuit should be considered. A rotary potentiometer employs a rotary slide member connected to a variable wire wound resistor that changes resistance to be equated to the angular position of the device that is monitored. Other principles of operations are same as that of linear potentiometer.

42. 01-09-2022 42 Potentiometric Sensor Potentiometer level sensors Figure shown below depicts gravitational fluid level sensor using a float. As the liquid level changes either on upward direction or downward direction than float position changes. This results into variation in the wiper arm across the resistance. This results into measurement of level position.

43. 01-09-2022 43 Gravitational Sensor: Gravitational Sensor: A gravity sensor measures the direction and intensity of gravity. Using such data, we can check the relative direction of a device within a space. A linear accelerometer provides data on acceleration, excluding gravity. In other words, a linear accelerometer measures the acceleration, excluding the impact of gravity on a certain object. Using this sensor, we can find out how fast a car is driving. With a gravity sensor and a linear accelerometer, a navigation application allows you to track the direction of a car.

44. 01-09-2022 44 Capacitive Sensor: A capacitive sensor is a passive sensor that works on the principle of variable capacitances. It is used to measure physical quantities such as displacement, pressure, etc. Construction of capacitive sensors: A capacitive sensors contains two conducting parallel metal plates separated by a dielectric medium. Working Principle of capacitive sensors: The capacitance between these two plates can be expressed as Where  ϵ  is the permittivity of the medium,  A  is the area of the plates and  d  is the distance between two plates. The capacitance of the sensors is measured using the bridge circuit. The output impedance of the sensors is given by Where  C  is the capacitance and  f  is the frequency of excitation. So a capacitive sensors can be used to measure the mechanical vibrations

45. 01-09-2022 45 Capacitive Sensor: The capacitance between two plates can be varied by any of the following methods. By changing the distance between two plates ( d ) By changing the permittivity of the dielectric medium ( ϵ ) By changing the area of overlapping of plates ( A )

46. 01-09-2022 46 Capacitive Sensor: By changing the distance between two plates: The capacitance can be varied by changing the distance between two plates. From the equation for C, we can observe that C and d are inversely proportional to each other. That is, the capacitance value will decrease with increasing distance and vice-versa. This principle can be used in a sensor by making the left plate fixed and the right plate movable by the displacement that is to be measured as shown in the figure. The change in distance between two plates will vary the capacitance of the sensors. Change in capacitance can be calibrated in terms of the measurand. These types of sensors are used to measure extremely small displacements. The distance capacitance curve is shown in the figure.

47. 01-09-2022 47 Capacitive Sensor: By changing the permittivity of the dielectric medium: Another method to change the capacitance value is by changing the permittivity of the dielectric material (ϵ). The permittivity and capacitance value are directly proportional to each other. In this arrangement, a dielectric material is filled into the space between the two fixed plates. It can be moved using the arm. This causes a variation in dielectric constant in the region. The change in dielectric constant will vary the capacitance of the sensors.

48. 01-09-2022 48 Capacitive Sensor: By changing the area of overlapping of plates: The capacitance can also be changed by varying the area of overlapping of plates. As shown in the figure, one plate is kept fixed and the other movable. When the plate is moved, the area of overlapping of plates changes, and the capacitance also changes. The capacitance value and area are directly proportional to each other. These types of sensors are used to measure relatively large displacements. The distance-capacitance curve is shown in the figure

49. 01-09-2022 49 Capacitive Sensor: Capacitive level measurement There is a probe inserted at the middle of the tank which is a dielectric material. The probe form one electrode of the capacitor and the metal sheet at the walls form the other. Capacitance is measured across the probe and the metal plate on the wall. The liquid inside the tank forms the dielectric material of the capacitor if the liquid is non-conductive. If the liquid is conductive then we have to cover the probe with a dielectric sheath to deliver a capacitance function.

50. 01-09-2022 50 Capacitive Sensor: Advantages of capacitive sensors Sensitivity is high. Requires small power to operate. Loading effect is low because of high input impedance. Good frequency response. Disadvantages Limited in its application for products of changing electrical properties (especially moisture content)

51. 01-09-2022 51 Inductive Sensor: An inductive sensor is a device that uses the principle of electromagnetic induction to detect or measure objects. An inductor develops a magnetic field when a current flows through it; alternatively, a current will flow through a circuit containing an inductor when the magnetic field through it changes. This effect can be used to detect metallic objects that interact with a magnetic field. The inductive sensor is based on Faraday's law of induction. The temporal variations of the Magnetic Flux Φ through a N turns circuit will induce a voltage e which follows: by assuming that the induced magnetic field B is homogeneous over a section S (the Magnetic flux will be expressed Φ = B X S

52. 01-09-2022 52 Inductive Sensor: Designed for non-contact measurement of displacement, distance, position, oscillation and vibrations. They are particularly suitable when high precision is required in harsh industrial environments (pressure, dirt, temperature) Inductive Proximity Sensor: An inductive sensor is a non-contact type of sensor, helpful in the detection of metallic objects. It can sense ferrous as well as non-ferrous materials. The sensing range is up to 100 mm. However, the level of sensitivity defers while sensing non-ferrous material. Look at the table below.

53. 01-09-2022 53 Inductive Sensor: Sensitivity when different objects are present, Sn = Operating distance Fe37 (Iron) 1 x Sn Stainless Steel 0.9 x Sn Brass bronze 0.5 x Sn Copper 0.4 x Sn Aluminum 0.4 x Sn An inductive proximity sensor consists of four elements – the coil, the oscillator, the trigger circuit, and an output.

54. 01-09-2022 54 Inductive Sensor: Coil: The coil generates the necessary electromagnetic field. Cup-shaped ferrite magnetic core holds the coil inside. The cup-shaped core is necessary to concentrate the coil magnetic field on the front area of the sensor. Oscillator: The oscillator is generally an LC oscillator. It produces radio frequency (100 kHz to 1 MHz) which helps to generate an electromagnetic field. Trigger Circuit: The trigger circuit senses the change in amplitude of oscillation and gives the signal to solid-state output. Output Circuit: The output circuit has a transistor NPN or PNP. After receiving the gate signal, the transistor switches ON and gives an output .

55. 01-09-2022 55 Inductive Sensor: Working Principle of Inductive Proximity Sensor: When a metal target enters the magnetic field created by coil, eddy current circulates within the target. This causes load on the sensor which decreases the oscillator’s amplitude. As the target reaches close to the sensor further the oscillator’s amplitude decreases. The trigger circuit is normally a Schmitt trigger. It monitors the amplitude of an oscillator. If the oscillator’s amplitude reaches a predetermined level, the trigger circuit gives the signal to the output circuit to switch-ON the output.

56. 01-09-2022 56 Inductive Sensor: Application of Inductive Proximity Sensors You can use an Inductive proximity sensor to count the metal cans. Inductive Sensor counting tins application Can be used to monitor the rotational speed of the machine. In conveyor application, you can use it to monitor the position. In a pipe manufacturing plant, the sensors are best for metal pipe detection for further processing of pipe. Robotic arm control is possible with the help of inductive sensors. The monitoring and counting can be done without actually touching the target. That is the biggest advantage.

57. 01-09-2022 57 Inductive Sensor: Advantages of Inductive Proximity Sensors Contactless sensing. High switching rate. Long-life as no moving parts are there. Easy installation. It can withstand harsh environmental conditions. It has very predictable results and performance.   Disadvantages of Inductive Proximity Sensors Can sense only metal. The sensing range of an inductive sensor dependents on the type of metal being detected, its shape, its size and also coil size used in the design. Due to above reason, inductive sensor has distance limitations for sensing Range detection limitation. The maximum detection range is 100mm.

58. 01-09-2022 58 Magnetic Sensor: A magnetic sensor is a sensor that detects the magnitude of magnetism and geomagnetism generated by a magnet or current. There are many different types of magnetic sensors. This section explains the typical sensor types and their features. Coils:

59. 01-09-2022 59 Magnetic Sensor: Coils: Coils are the simplest magnetic sensors that can detect changes of the magnetic flux density. As shown in Figure 1, when a magnet is brought close to the coil, the magnetic flux density in the coil increases by ΔB. Then, an induced electromotive force/induced current that generates a magnetic flux in a direction that hinders an increase in magnetic flux density is generated in the coil. Conversely, moving the magnet away from the coil reduces the magnetic flux density in the coil, so induced electromotive force and induced current will be generated in the coil to increase the magnetic flux density. Also, since there is no change in the magnetic flux density when the magnet is not moved, no induced electromotive force or induced current will be generated. By measuring the direction and magnitude of this induced electromotive force, it is possible to detect the change in magnetic flux density. Because of its simple structure, a coil is not easily damaged. However, the output voltage depends on the rate of change of the magnetic flux. It may not be possible to use a coil to detect a fixed magnet or magnetic flux that changes very slowly.

60. 01-09-2022 60 Magnetic Sensor: 2) Reed Switch A reed switch is a sensor in which metal pieces (reed) extending from both the left and right sides are enclosed in a glass tube with a gap at the overlapping position of the reeds. When a magnetic field is applied externally, these reeds are magnetized. When the reeds are magnetized, the overlapping parts attract each other and come into contact, then the switch turns on.

61. 01-09-2022 61 Magnetic Sensor: 3 ) Hall Effect Sensor: Hall effect sensor is a magnetic sensor Hall Effect Sensor is the solid-state device which switches to active state when it is introduced in magnetic field. The output voltage of hall effect sensor is dependent on magnetic field around it. When the magnetic field across the semiconductor slab changes the magnetic flux density also changes due to which the output voltage of hall effect sensor varies. Principle of Hall Effect Sensor: The hall effect sensor works on the principle of hall effect.

62. 01-09-2022 62 Magnetic Sensor: Principle of Hall Effect Sensor: The hall effect sensor works on the principle of hall effect. According to hall effect when a semiconductor slab is placed in magnetic field provided that magnetic field lines are perpendicular to the axis of semiconductor specimen and current is allowed to pass along the axis of semiconductor specimen then the charges carriers of the semiconductor device experiences magnetic force. Due to this magnetic force they are pushed sidewards i.e towards the edges of the slab. As a consequence of this the electric field is created due to accumulation of charge carriers across the edges . Thus, the output voltage varies with the variation in the magnetic field. Hall effect is based on the Lorentz principle. Hall Effect sensors uses this phenomenon of Hall effect for sensing fundamental quantities such as position, velocity, polarity etc. The two crucial term associated with magnetic field are magnetic flux density and polarity (North Pole and South Pole). The hall effect sensors uses these terms for sensing. The output voltage generated by the sensor is directly dependent on magnetic flux density. Thus, if magnetic field across the sensor changes the output from hall effect also changes. In this way it provides sensing operation.

63. 01-09-2022 63 Magnetic Sensor: Applications of Hall Effect Sensor Hall Effect Sensors are used for sensing positions thus, they are often used as proximity sensors. They can also be used in the application in which we use optical and light sensors. Hall effect sensors are better to use because optical and light sensors are likely to get affected by environmental conditions while Hall Effect sensors can also work efficiently in the dust, air or other external environmental factors.

64. 01-09-2022 64 Optical Sensor: Optical Position Sensors Optical position sensors operate using one of two principles. In the first type, light is transmitted from an emitter and sent over to a receiver at the other end of the sensor. In the second type, the emitted light signal is reflected from the object being monitored returned towards the light source. A change in the light characteristics (e.g. wavelength, intensity, phase, polarization) is used to establish information about the object’s position.

65. 01-09-2022 65 Optical Sensor: Optical Displacement Sensor Principle: Light is sent through a transmitting fiber and is made to fall on a moving target. The reflected light from the target is sensed by a detector. With respect to intensity of light reflected from its displacement of the target is measured. Description:  It consists of a bundle of transmitting fibers coupled to the laser source and a bundle of receiving fibers coupled to the detector as shown in the figure. The axis of the transmitting fiber and the receiving fiber with respect to the moving target can be adjusted to increase the sensitivity of the sensor

66. 01-09-2022 66 Optical Sensor: Working: Light from the source is transmitted through the transmitting fiber and is made to fall on the moving target. The light reflected from the target is made to pas through the receiving fiber and the same is detected by the detector. Based on the intensity of the light received, the displacement of the target can be measured, (i.e.) if the received intensity is more than we can say that the target is moving towards the sensor and if the intensity is less, we can say that the target is moving away from the sensor.  Application as MEDICAL ENDOSCOPE Optical fibers are very much useful in medical field. Using low quality, large diameter and short length silica fibers we can design a fiber optic endoscope or fibroscope A medical endoscope is a tubular optical instrument, used to inspect or view the internal parts of human body which are not visible to the naked eye. The photograph of the internal parts can also be taken using this endoscope.

67. 01-09-2022 67 Optical Sensor: Optical level Sensor

68. 01-09-2022 68 Optical Sensor: Optical level Sensor The working principle of the optical water level sensor, the product contains a infrared light-emitting diode and a photosensitive receiver. The light emitted by the LED is directed into the lens at the top of the sensor. When the liquid is immersed in the lens of the photoelectric level switch, the light is refracted into the liquid, so that the receiver does not receive or can only receive a small amount of light. The tank infrared level sensor in operating conditions, and the receiver can drive an internal electrical switch to activate an external alarm or control circuit. If there is no liquid, the light from the LED is reflected directly from the lens back to the receiver.  The optical level sensor will output a high voltage value or a low vlotage value according to water state or waterless state. When the prism of level sensor is in liquid, the level sensor will output a low voltage; When the prism of level sensor is in air, the level sensor will output a high voltage.  

69. 01-09-2022 69 Radar Sensor: The sensor which is used to measure the distance, velocity and movements of objects above wide distances is known as a radar sensor and also measures the relative speed of the noticed object. This sensor uses wireless detecting technology like FMCW (Frequency Modulated Continuous Wave) to detect the motion by figuring out the object’s shape, position, motion trajectory & motion characteristics. As compared to other types of sensors, these sensors are not affected by darkness & light. These sensors can detect longer distances & it is secure for people & animals. Here the carrier frequency is modulated constantly in a small range of bandwidth. Once the signal from an object is reflected back, then it is feasible to determine the distance & also the object speed by comparing frequency. This sensor uses an extremely high carrier frequency to produce a very thin beam cone and also notices even small objects without interference from adjacent objects above large distances.

70. 01-09-2022 70 Radar Sensor: Radar Sensor Working Principle The working principle of a radar sensor is to compute the speed of an object along with its direction by detecting the change in frequency wave which is known as Doppler Effect. A radar sensor includes an antenna that emits a high-frequency (62 GHz) transmitted signal. This transmitted signal also includes a modulated signal with a lower frequency (10 MHz). This sensor gets the signal once it is returned back from an object. So this sensor evaluates the phase shift between the two frequencies. Here, the difference in transmitting time & receiving time will determine the distance between the sensor & an object.

71. 01-09-2022 71 Radar Sensor: Automotive Radar Sensor Block Diagram The block diagram of the 24 GHz wideband & short-range automotive radar sensor is shown below. This block diagram includes a VCO, PRF (pulse repetition frequency), LNA (low noise amplifier), DSP (digital signal processing) & two antennas.

72. 01-09-2022 72 Radar Sensor: VCO: The term VCO stands for voltage-controlled oscillator which is used to generate an o/p signal whose frequency changes with the amplitude of voltage for an input signal above a reasonable frequencies range. Power Splitter: A power splitter or power divider is used to divide a single RF line into above one line & split the power. Power Amplifier: A power amplifier is used to change a signal from a low-power to a higher power. SP (Signal Processing): Signal processing focuses on modifying, synthesizing & analyzing signals like images, sound, & scientific measurements. PRF (Pulse Repetition Frequency): The pulse repetition frequency is the number of pulses of a repeating signal within a specific unit time, usually measured in pulses for each second. Mixer: The mixer is used to generate both the frequencies sum & difference which are applied to it. So the frequencies difference will be of IF (Intermediate Frequency) type. LNA (Low Noise Amplifier): It is used to amplify the weak RF signal and this signal is received by using an Antenna. This amplifier’s output can be connected to Mixer. Antennas: This system includes transmit & receive channels where the transmit channels are mainly used to drive different antennas & also provide beam steering capabilities. Multiple receive channels provide the angular data regarding the target because there is a phase difference between received signals by dissimilar receive antennas.

73. 01-09-2022 73 Radar Sensor: The concept used by the 24 GHz SRR (Short Range Radar) sensors is pulsed radar. This sensor includes the transmitting & receiving path, the control & DSP (digital signal processing) circuits. The target at range ‘R’ can be detected by measuring the elapsed time in between a transmitter signal & a correlated received signal. Application: The main aim of this radar sensor is to decrease potential danger & traffic accidents faced by the vehicle driver. In this system, different sensors are located in different places of the car so that the exact measurement of object distance & speed of objects in front, behind, or beside. Every sensor in this system transmits the signals to calculate, if there is anybody in the region of the car then informs the driver regarding it. These signals cover upto 30 m distance but, if the distance in between the target & car was less than two meters, then the car generates an alarm sound to give an alert to the driver so that the car driver can take the appropriate action to avoid a collision.

74. 01-09-2022 74 Radar Sensor: Radar Sensor Types There are different types of radar sensors which include the following

75. 01-09-2022 75 Radar Sensor: Millimeter -Wave Radar Sensor The sensor which uses millimeter waves is known as a millimeter -wave radar sensor. Generally, millimeter waves have a 30 to 300 GHz frequency domain. Among them, 77Ghz & 24Ghz radar sensors are used in automobiles for collision avoidance. The millimeter -wave wavelength ranges in between centimeter wave & lightwave . The advantages of millimeter -wave are photoelectric guidance and microwave guidance. Millimeter -wave radar has many characteristics as compared to centimeter wave radar-like spatial resolution is high, simple integration, and small size. As compared to optical sensors like lasers, infrared, cameras, this sensor has a strong capacity to penetrate smoke, dust, fog & anti-interference capacity. These radar sensors are used in security, automotive electrons, intelligent transportation, and drones.

76. 01-09-2022 76 Radar Sensor: CW Doppler Radar Sensor A CW Doppler radar sensor or continuous wave Doppler radar operates at 915 MHz frequency. This radar sensor works with Doppler Effect for measuring the object’s speed at various distances. This sensor transmits a microwave signal to a target & analyzes the change in frequency in the reflected signal, the difference between the reflected & transmitted frequencies, and also measures the target speed precisely which is relative to the radar.

77. 01-09-2022 77 Radar Sensor: FMCW Radar Sensor The term “FMCW” stands for frequency modulated continuous wave radar. This sensor frequency will be changed with the time based on the triangle wave’s law. The echo signal frequency which is received by the radar is similar to the emission frequency. They both are triangular waves but there is a tiny difference in time. So this tiny difference is used to calculate the target distance.

78. 01-09-2022 78 Radar Sensor: Advantages The radar sensor is independent of different weather conditions Bears excessive cold & heat It works in bad lighting conditions It works in the dark Its maintenance is free It provides a great range of functions This sensor is used for indoor & outdoor purposes This sensor has many features as compared to other sensors

79. 01-09-2022 79 Radar Sensor: Disadvantages The  disadvantages of radar sensors  include the following. It cannot differentiate & resolve numerous targets which are extremely close like our eye. It cannot identify the color of the objects. It cannot observe objects which are too deep and in the water.

80. 01-09-2022 80 Radar Sensor: Applications The applications of radar sensors include the following. Radar sensors are used where vehicle detection is required or avoiding a collision when equipment is moving. Vehicle detection mainly includes trucks, trains, cars, toll booths, shipping canals, railroads, etc. Collision avoidance includes ports, manufacturing, low-visibility factory environments & onboard mobile equipment. Military Security system Automotive electrons Intelligent traffic radar UAV radar Intelligent lighting Industrial control Medical treatment Sports

81. 01-09-2022 81 Radar Sensor Vs Ultrasonic Sensor Radar Sensor Ultrasonic Sensor The radar sensor is used to change the signals from microwave echo to electrical. An ultrasonic sensor is used to measure the distance to an object with ultrasonic sound waves. These sensors work with electromagnetic waves. These sensors work by producing sound waves. Similar to ultrasonic, the waves from this sensor will reflect the target & travel at a known speed very fast. The sound waves travel at the speed of sound to the target where they reflect the target & come back to the sensor. The electromagnetic waves of this sensor will respond in a different way to particular materials because they are reflected off the exterior. The sound waves of this sensor will not respond to particular materials. These sensors are affected through different variables These sensors are affected by temperature. These sensors are used in oil & gas, pulp & paper, clarifiers, granular solids, plastic pellets, pharmaceuticals, etc. These sensors are used for measuring the flow of liquid, solids level, open-channel flow, object profiling & presence detection.

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