Sensors and transducers Working,Applications
- 1. SENSORS & TRANSDUCERS AADHAN K N - 2019119001 ANJUM JANNATH - 2019119002 ARSSHIDA S - 2019119003
- 2. SENSORS
- 3. WHAT IS A SENSOR ? A sensor is a device that responds to some type of the input from the environment such as heat, light, motion, temperature, pressure and moisture. Sensors are used to switch currents and voltages. Every sensor has three terminals: Vcc, GND and output. Vcc is used to power up the sensor; to provide a fixed negative reference, ground is used, and the output of the sensor is analog. But in some sensors, there may be more than one output terminals. Sensor converts the physical gesture into electrical signals and do different works.
- 4. `1Different types of sensor and their working
- 5. Working of an “IR LED” • IR ` is very popular sensor, which is used in many applications in electronics, like it is used in Remote control system, motion detector, Product counter, Line follower Robots, Alarms etc. • IR sensor basically consist an IR LED and a Photodiode, this pair is generally called IR pair or Photo coupler. IR sensor work on the principal in which IR LED emits IR radiation and Photodiode sense that IR radiation. Photodiode resistance changes according to the amount of IR radiation falling on it, hence the voltage drop across it also changes and by using the voltage comparator (like LM358) we can sense the voltage change and generate the output accordingly.
- 6. Photo Diode (Light Sensor) Photodiode is considered as Light dependent Resistor (LDR), means it has very High resistance in absence of light and become low when light falls on it. Photodiode is a semiconductor which has a P-N junction, operated in Reverse Bias, means it start conducting the current in reverse direction when Light falls on it, and the amount of current flow is proportional to the amount of Light. This property makes it useful for IR detection. is a semiconductor device which is used to detect the light rays and mostly used as IR Receiver. Its construction is similar to the normal PN junction diode but the working principle differs from it. As we know a PN junction allows small leakage currents when it is reverse biased so, this property is used to detect the light rays. So, in this way, a photodiode can be used to sense the light rays and maintain the current through the circuit. Photodiode looks like a LED, with a Black colour coating on its outer side. It is used in reversed biased, as showed in circuit diagram below.
- 7. LDR (Light Dependent Resistor): As the name itself specifies that the resistor that depends upon the light intensity. It works on the principle of photoconductivity which means the conduction due to the light. It is generally made up of Cadmium sulphide. When light falls on the LDR, its resistance decreases and acts similar to a conductor and when no light falls on it, its resistance is almost in the range of MΩ or ideally it acts as an open circuit. One note should be considered with LDR is that it won’t respond if the light is not exactly focused on its surface.
- 8. Thermistor (Temperature Sensor) A thermistor can be used to detect the variation in temperature. It has a negative temperature coefficient that means when the temperature increases the resistance decreases. So, the thermistor’s resistance can be varied with the rise in temperature which causes more current flow through it. This change in current flow can be used to determine the amount of change in temperature. An application for thermistor is, it is used to detect the rise in temperature and control the leakage current in a transistor circuit which helps in maintaining its stability. Thermistor is temperature sensitive resistor, whose resistance changes according to the temperature. There are two types of thermistor NTC (Negative Temperature Co-efficient) and PTC (Positive Temperature Co- efficient), we are using a NTC type thermistor. NTC thermistor is a resistor whose resistance decreases as rise in temperature while in PTC it will increase the resistance as rise in temperature. We also used Thermistor in many interesting applications like Fire alarm circuit using Thermistor, Temperature Controlled AC, Thermistor Based Thermostat Circuit.
- 9. Thermocouple (Temperature Sensor) Another component that can detect the variation in temperature is a thermocouple. In its construction, two different metals are joined together to form a junction. Its main principle is when the junction of two different metals is heated or exposed to high temperatures a potential across their terminals varies. So, the varying potential can be further used to measure the amount of change in temperature.
- 10. Strain Gauge (Pressure/Force Sensor): A strain gauge is used to detect pressure when a load is applied. It works on the principle of resistance; we know that the resistance is directly proportional to the length of the wire and is inversely proportional to its cross-sectional area (R=ρl/a). The same principle can be used here to measure the load. On a flexible board, a wire is arranged in a zig-zag manner as shown in the figure below. So, when the pressure is applied to that particular board, it bends in a direction causing the change in overall length and cross- sectional area of the wire. This leads to change in resistance of the wire. The resistance thus obtained is very minute (few ohms) which can be determined with the help of the Wheatstone bridge. The strain gauge is placed in one of the four arms in a bridge with the remaining values unchanged. Therefore, when the pressure is applied to it as the resistance changes the current passing through the bridge varies and pressure can be calculated.
- 11. Strain gauges are majorly used to calculate the amount of pressure that an airplane wing can withstand and it is also used to measure the number of vehicles allowable on a particular road etc.
- 12. Load Cell (Weight Sensor): Load cells are similar to strain gauges which measure the physical quantity like force and give the output in form of electrical signals. When some tension is applied on the load cell it structure varies causing the change in resistance and finally, its value can be calibrated using a Wheatstone bridge. The bridge is used for finding the value of an unknown resistance connected with two known resistor, one variable resistor and a galvanometer. To find the value of unknown resistance the
- 13. deflection on galvanometer made to zero by adjusting the variable resistor. This point is known as balance point of Wheatstone bridge.
- 14. Potentiometer: A potentiometer is used to detect the position. It generally has various ranges of resistors connected to different poles of the switch. A potentiometer can be either rotary or linear type. In rotary type, a wiper is connected to a long shaft which can be rotated. When the shaft has rotated the position of the wiper alters such that the resultant resistance varies causing the change in the output voltage. Thus, the output can be calibrated to detect the change its position.
- 15. Encoder To detect the change in the position an encoder can also be used. It has a circular rotatable disk-like structure with specific openings in between such that when the IR rays or light rays pass through it only a few light rays get detected. Further, these rays are encoded into a digital data (in terms of binary) which represents the specific position. The graphic at right outlines the basic construction of an incremental rotary encoder using optical technology. A beam of light emitted from an LED passes through the Code Disk, which is patterned with opaque lines (much like the spokes on a bike wheel). As the encoder shaft
- 16. Hall Sensor: The name itself states that it is the sensor which works on the Hall Effect. It can be defined as when a magnetic field is brought close to the current carrying conductor (perpendicular to the direction of the electric field) then a potential difference is developed across the given conductor. Using this property, a Hall sensor is used to detect the magnetic field and gives output in terms of voltage. Care should be taken that the Hall sensor can detect only one pole of the magnet. The hall sensor is used in few smartphones which are helpful in turning off the screen when the flap cover (which has a magnet in it) is closed onto the screen. Here is one practical application of Hall Effect sensor in Door Alarm.
- 17. Flex Sensor: A FLEX sensor is a transducer which changes its resistance when its shape is changed or when it is bent. A FLEX sensor is 2.2 inches long or of finger length. It is shown in the figure. Simply speaking the sensor terminal resistance increases when it’s bent. This change in resistance can do no good unless we can read them. The controller at hand can only read the changes in voltage and nothing less, for this, we are going to use voltage divider circuit, with that we can derive the resistance change as a voltage change.
- 18. Microphone (Sound Sensor): Microphone can be seen on all the smartphones or mobiles. It can detect the audio signal and convert them into small voltage (mV) electrical signals. A microphone can be of many types like condenser microphone, crystal microphone, carbon microphone etc. each type of microphone work on the properties like capacitance, piezoelectric effect, resistance respectively. Let us see the operation of a crystal microphone which works on the piezoelectric effect. A bimorph crystal is used which under pressure or vibrations produces proportional alternating voltage. A diaphragm is connected to the crystal through a drive pin such that when the sound signal hits the diaphragm it moves to and from, this movement changes the position of the drive pin which causes vibrations in the crystal thus an alternating voltage is generated with respect to the applied sound signal. The obtained voltage is fed to an amplifier in order to increase the overall strength of the signal.
- 19. Ultrasonic sensor: Ultrasonic means nothing but the range of the frequencies. Its range is greater than audible range (>20 kHz) so even it is switched on we can’t sense these sound signals. Only specific speakers and receivers can sense those ultrasonic waves. This ultrasonic sensor is used to calculate the distance between the ultrasonic transmitter and the target and also used to measure the velocity of the target. Ultrasonic sensor HC-SR04 can be used to measure distance in the range of 2cm-400cm with an accuracy of 3mm. Let’s see how this module works. The HCSR04 module generates a sound vibration in ultrasonic range when we make the ‘Trigger’ pin high for about 10us which will send an 8-cycle sonic burst at the speed of sound and after striking the object, it will be received by the Echo pin. Depending on the time taken by sound vibration to get back, it provides the appropriate pulse output. We can calculate the distance of the object based on the time taken by the ultrasonic wave to return back to the sensor.
- 20. Touch Sensor: In this generation, we can say that almost all are using smartphones which have widescreen that too a screen which can sense our touch. So, let’s see how this touchscreen works. Basically, there are two types of touch sensors resistive based and a capacitive based touch screen. Let’s know about working of these sensors briefly. The resistive touchscreen has a resistive sheet at the base and a conductive sheet under the screen both of these are separated by an air gap with a small voltage applied to the sheets. When we press or touch the screen the conductive sheet touches the resistive sheet at that point causing current flow at that particular point, the software senses the location and relevant action is performed. Whereas capacitive touch works on the electrostatic charge that is available on our body. The screen is already charged with s the all-electric field. When we touch the screen a close circuit forms due to electrostatic charge that flow through our body. Further, software decides the location and the action to be performed. We can observe that capacitive
- 21. touch screen won’t work when wear hand gloves because there won’t be conduction between the finger(s) and the screen.
- 22. PIR sensor: PIR sensor stands for Passive Infrared sensor. These are used to detect the motion of humans, animals or things. We know that infrared rays have a property of reflection. When an infrared ray hits an object, depending upon the temperature of the target the infrared ray properties changes, this received signal determines the motion of the objects or the living beings. Even if the shape of the object alters, the properties of the reflected infrared rays can differentiate the objects precisely. Passive Infrared Sensor (PIR) is very useful module, used to build many kinds of Security Alarm Systems and Motion Detectors. It is called passive because it receives infrared, not emits. Basically, PIR sensor detects any change in heat, and whenever it detects any change, its output PIN becomes HIGH. They are also referred as Pyroelectric or IR motion sensors. Here we should note that every object emits some amount of infrared when heated. Human also emits infrared because of body heat. PIR sensors can detect small amount of variation in infrared. Whenever an object passes through the sensor range, it produces infrared because of the friction between air and object, and get caught by PIR.
- 23. he main component of PIR sensor is Pyroelectric sensor shown in figure (rectangular crystal behind the plastic cap). Along with this, BISS0001 ("Micro Power PIR Motion Detector IC"), some resistors, capacitors and other components used to build PIR sensor. BISS0001 IC take the input from sensor and does processing to make the output pin HIGH or LOW accordingly. Pyroelectric sensor divides in two halves, when there is no motion, both halves remain in same state, means both senses the same level of infrared. As soon as somebody enters in first half, the infrared level of one half becomes greater than other, and this causes PIRs to react and makes the output pin high. Pyroelectric sensor is covered by a plastic cap, which has array of many Fresnel Lens inside. These lenses are curved in such a manner so that sensor can cover a wide range.
- 24. Accelerometer (Tilt Sensor): An accelerometer sensor can sense the tilt or movement of it in a particular direction. It works based on the acceleration force caused due to the earth’s gravity. The tiny internal parts of it are such sensitive that those will react to a small external change in position. It has a piezoelectric crystal when tilted causes disturbance in the crystal and generates potential which determines the exact position with respect to X, Y and Z axis.
- 25. Gas sensor: In industrial applications gas sensors plays a major role in detecting the gas leakage. If no such device is installed in such areas it ultimately leads to an unbelievable disaster. These gas sensors are classified into various types based on the type of gas that to be detected. Let’s see how this sensor works. Underneath a metal sheet there exists a sensing element which is connected to the terminals where a current is applied to it. When the gas particles hit the sensing element, it leads to a chemical reaction such that the resistance of the elements varies and current through it also alters which finally can detect the gas.
- 26. APPLICATIONS Transportation: Oxygen sensors for reefer containers and controlled atmosphere fruit storage and transportation. Telecom: Liquid detection sensors for immediate leak detection alarming Industrial: Oxygen sensors for combustion optimization. Liquid level sensors for water, coolant and oil level control Aviation: Oxygen sensors used in OBIGGS and OBOGGS aerospace applications. Level sensors for hydraulic fuel reservoirs.
- 27. Marine: Oxygen sensors for inert atmospheres in safety and transportation systems. Overspill protection using single point liquid level switches. Medical: Control of tank levels in water baths. Oxygen sensors for incubators and respiratory systems. Level Control: Intelligent single point level switches to detect the presence or absence of all types of liquids.
- 28. TRANSDUCERS
- 29. WHAT IS A TRANSDUCER ? It uses the principle of Transduction (The process whereby a transducer converts energy from one form to another) to convert the measurand into a usable output. Based on these definitions, a Piezoelectric Crystal is the Sensor whereas a Piezoelectric Crystal with electrodes and some sort of input/output mechanism attached to it makes it a Transducer.
- 30. HOW DOES IT WORK ? A transducer, combination of detecting and transduction element, has to change one form of energy into other. The sensing element (known as Detecting Element/primary transducer as it is the first in the process of conversion of one form of energy into other) responds to the physical change and generates its output. This output may be in the form of displacement, angular displacement, strain etc. The output of the sensing element is then linked to the transduction element (part of transducer which converts the output of sensing element into electrical signal). This element is so designed to act upon the response of sensing element and generate a proportional output in the form of electrical signal.
- 32. ACTIVE AND PASSIVE TRANSDUCERS • Active transducers * These transducers do not need any external source of power for their operation. Therefore, they are also called as self generating type transducers. * It operates under energy conversion principle. * Examples – photovoltaic, thermoelectric, electromagnetic, piezoelectric, etc., • Passive transducers * These transducers need external source of power for their operation. So they are not self generating type transducers. * A DC power supply or an audio frequency generator is used as an external power source. * Examples – thermistor, potentiometer type transducer.
- 33. PRIMARY AND SECONDARY TRANSDUCERS Some transducers contain the mechanical as well as electrical device. • Primary transducers The mechanical device converts the physical quantity to be measured into a mechanical signal. Such mechanical device are called as the primary transducers, because they deal with the physical quantity to be measured. • Secondary transducers The electrical device then convert this mechanical signal into a corresponding electrical signal. Such electrical devices are known as secondary transducers.
- 34. ANALOG AND DIGITAL TRANSDUCERS • Analog transducers * These transducers convert the input quality into an analog output which is a continuous function of time. * Thus a strain gauge, an L.V.D.T., a thermocouple or a thermistor may be called as analog transducers as they give an output within a continuous function of time. • Digital transducers * These transducers convert the input quality into an electrical output which is in the form of pulses and its output is represented by 0 and 1.
- 35. TRANSDUCER AND INVERSE TRANSDUCER • Transducer Transducers convert non – electrical quantity to electrical quantity. • Inverse transducer Inverse transducers convert electrical quantity to non – electrical quantity. A piezoelectric crystal acts as an inverse transducer because when a voltage is applied across its surfaces, it changes its dimensions causing a mechanical displacement.
- 36. APPLICATIONS • The transducer measures the load on the engines. • It is used as a sensor for knowing the engine knock. • The transducers measure the pressure of the gas and liquid by converting it into an electrical signal. • It converts the temperature of the devices into an electrical signal or mechanical work. • The transducer is used in the ultrasound machine. It receives the sound waves of the patient by emitting their sound waves and pass the signal to the CPU. • The transducer is used in the speaker for converting the electrical signal into acoustic sound. • It is used in the antenna for converting the electromagnetic waves into an electrical signal.
- 37. THANK YOU