Module 5 Sensors and Actuators PDF

Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited...

Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited LSPU Self-Paced Learning Module (SLM) Course ECE 8: Electronics 3 Sem/AY First Semester/2024-2025 Module No. 5 Lesson Title Sensors and Actuators Week Duration Date This lesson will discuss the sensors and transducers. This lesson will also provide Description activities and exercises that will practice the students’ competence in understanding of the optoelectronic device. Lesson Learning Outcomes Intended Students should be able to meet the following intended learning outcomes: Learning Describe what is transducer Outcomes Identify the difference between sensor and actuator Discuss different sensors and actuators Targets/ At the end of the lesson, students should be able to: Objectives Know what is a transducer Differentiate sensor and actuator Discuss and design an application of transducer Student Learning Strategies Online Activities A. Online Discussion via Google Meet (Synchronous/ You will be directed to attend in a 2-Hour class discussion/activity about transducer. To have access to the Online Discussion, refer to this Asynchronous) link: ____________________. The online discussion will be announced. (For further instructions, refer to your Google Classroom and see the schedule of activities for this module) LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited B. Learning Guide Questions: 1. What is transducer? 2. What are the two types of transducer? 3. What devices are use as a sensor?as an actuator 4. Discuss an application Note: The insight that you will post on online discussion forum using Learning Management System (LMS) will receive additional scores in class participation. Lecture Guide Transducer - Is a device, usually electrical, electronic, or electro – mechanical, that converts one type of energy to another for the purpose of measurement or information transfer Two general types of transducer 1. Input transducers Offline Activities - Convert a quantity to an electrical signal (voltage) or to resistance (which can be converted to voltage) (e-Learning/Self- - Used to sense a wide range of different energy forms such as movement, Paced) electrical signals, radiant energy, thermal or magnetic energy - Also called as sensors 2. Output transducer - Convert an electrical signal to another quantity - electromechanical devices that move, rotate, push, pull, and in general “make something happen” when electrical signals are sent to them - Also called as actuators General Control System Sensors and actuators are used to close the loop LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 1. General control system for transducer Example: 1. a microphone (input device) converts sound waves into electrical signals for the amplifier to amplify (a process), and a loudspeaker (output device) converts these electrical signals back into sound waves Figure 2. Sounds system LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Common Sensors and transducer Sensors - Produce a voltage or signal output response which is proportional to the change in the quantity that they are measuring (the stimulus) - The type or amount of the output signal depends upon the type of sensor being used Criteria to Choose a Sensor 1. Type of Sensing: The parameter that is being sensed like temperature or pressure. 2. Operating Principle: The principle of operation of the sensor. 3. Power Consumption: The power consumed by the sensor will play an important role in defining the total power of the system. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited 4. Accuracy: The accuracy of the sensor is a key factor in selecting a sensor. 5. Environmental Conditions: The conditions in which the sensor is being used will be a factor in choosing the quality of a sensor. 6. Cost: Depending on the cost of application, a low cost sensor or high cost sensor can be used. 7. Resolution and Range: The smallest value that can be sensed and the limit of measurement are important. 8. Calibration and Repeatability: Change of values with time and ability to repeat measurements under similar conditions. Basic Requirements of a Sensor or Transducer 1. Range: It indicates the limits of the input in which it can vary. In case of temperature measurement, a thermocouple can have a range of 25 – 250 0C. 2. Accuracy: It is the degree of exactness between actual measurement and true value. Accuracy is expressed as percentage of full range output. 3. Sensitivity: Sensitivity is a relationship between input physical signal and output electrical signal. It is the ratio of change in output of the sensor to unit change in input value that causes change in output. 4. Stability: It is the ability of the sensor to produce the same output for constant input over a period of time. 5. Repeatability: It is the ability of the sensor to produce same output for different applications with same input value. 6. Response Time: It is the speed of change in output on a stepwise change in input. 7. Linearity: It is specified in terms of percentage of nonlinearity. Nonlinearity is an indication of deviation of curve of actual measurement from the curve of ideal measurement. 8. Ruggedness: It is a measure of the durability when the sensor is used under extreme operating conditions. 9. Hysteresis: The hysteresis is defined as the maximum difference in output at any measurable value within the sensor’s specified range when approaching the point first with increasing and then with decreasing the input parameter. Hysteresis is a characteristic that a transducer has in being unable to repeat its functionality faithfully when used in the opposite direction of operation. Two types of sensor 1. Active sensor - require an external power supply to operate, called an excitation signal which is used by the sensor to produce the output signal. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - self-generating devices because their own properties change in response to an external effect producing for example, an output voltage of 1 to 10v DC or an output current such as 4 to 20mA DC - Can also produce signal amplification 2. Passive sensor - does not need any additional power source or excitation voltage - Instead a passive sensor generates an output signal in response to some external stimulus - direct sensors which change their physical properties, such as resistance, capacitance or inductance etc Analogue Sensor - Produce a continuous output signal or voltage which is generally proportional to the quantity being measured - Physical quantities such as Temperature, Speed, Pressure, Displacement, Strain etc are all analogue quantities as they tend to be continuous in nature - tend to produce output signals that are changing smoothly and continuously over time - tend to be very small in value from a few mico-volts (uV) to several milli-volts (mV), so some form of amplification is required. Op Amps are very useful in providing amplification and filtering. - Circuits which measure analogue signals usually have a slow response and/or low accuracy - can be easily converted into digital type signals for use in micro- controller systems by the use of analogue-to-digital converters\ Example: Figure 3. System used to measure the temperature using thermocouple LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited The temperature of a liquid can be measured using a thermometer or thermocouple which continuously responds to temperature changes as the liquid is heated up or cooled down Digital sensors - Produce a discrete digital output signals or voltages that are a digital representation of the quantity being measured - produce a Binary output signal in the form of a logic “1” or a logic “0”, (“ON” or “OFF”) - have very high accuracies and can be both measured and “sampled” at a very high clock speed - The accuracy of the digital signal is proportional to the number of bits used to represent the measured quantity Example Figure 4. Light Sensor that measures speed and produces a digital signal In our example above, the speed of the rotating shaft is measured by using a digital LED/Opto-detector sensor. The disc which is fixed to a rotating shaft (for example, from a motor or robot wheels), has a number of transparent slots within its design. As the disc rotates with the speed of the shaft, each slot passes by the sensor in turn producing an output pulse representing a logic “1” or logic “0” level. These pulses are sent to a register of counter and finally to an output display to show the speed or revolutions of the shaft. By increasing the number of slots or “windows” within the disc more output pulses can be produced for each revolution of the shaft LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Signal conditioning of sensors - Analogue signal produced by a sensor have an output of milli-volts or even pico-volts range and can be amplified many times over by a simple op-amp circuit. - Therefore, to provide any useful signal a sensors output signal has to be amplified with an amplifier that has a voltage gain up to 10,000 and a current gain up to 1,000,000 with the amplification of the signal being linear with the output signal being an exact reproduction of the input, just changed in amplitude - Also, when measuring very small physical changes the output signal of a sensor can become “contaminated” with unwanted signals or voltages that prevent the actual signal required from being measured correctly - Unwanted signals are called “Noise” and can be greatly reduced or eliminated using filtering techniques Figure 5. Op amp Filter Position Sensors - provide feedback on the position of the measurand (quantity being measured) - provide motion control, counting and encoding tasks by determining the presence or absence of a target or by detecting its direction, speed, motion or distance. - detect the position of an object or disturbance of electric or magnetic field and convert that physical parameter into an output electrical signal to indicate the position of the target Types of position sensor 1. Contact devices - Have the physical contact with the measurand. The contact based sensors are Limit Switches and Resistance based position sensors - provide simple and low cost solutions in applications where physical contact with the object is acceptable LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited 2. Non-contact devices - don’t involve in physical contact with the object - They are magnetic sensors, proximity sensors, Hall Effect based sensors and ultra-sonic sensors. Resistance Based or Potentiometric position Sensor Potentiometers - Resistive position sensors - They are originally developed for applications in military use - an work as linear or rotary position sensors - doesn’t require a power supply or extra circuitry to perform their basic position sensing function. Hence, they are passive device - Operates in two modes: voltage divider and rheostat Rheostat - the resistance varies with motion - the applications make use of this varying resistance between fixed terminal and a sliding contact Voltage divider mode - has the true potentiometric operation - a reference voltage is applied across a resistive element. The position of the movable wiper is determined by calculating the voltage picked up by the wiper Potentiometers are the most commonly used position sensors. It has a fixed terminal and a wiper terminal connected to a mechanical shaft. The movement can be either linear (slide) or angular (rotational). This movement causes the resistance between fixed and wiper terminals to change. The output electrical signal which is generally voltage varies in proportion to the position of the wiper resistive track and hence the value of the resistance. When used as a position sensor the moveable object is connected directly to the rotational shaft or slider of the potentiometer resistance is proportional to position LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 6. Potentiometer Potentiometer Construction The output signal (Vout) 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 Figure 7. Basic Construction Figure 8. Basic configuration LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Example of simple positioning circuit Figure 9. Simple position sensing circuit Advantage of Potentiometer Position Sensor 1. Low cost 2. Low tech 3. Easy to use Disadvantage 1. Wear due to moving parts 2. Low accuracy 3. Low repeatability 4. Limited frequency response 5. The range of movement of its wiper or slider is limited to the physical size of the potentiometer being used. Ex. fixed mechanical rotation of between 0o and about 240 to 3300 Types of potentiometers 1. Carbon Film potentiometer - the most common type of resistive track used in potentiometers - there is a contact noise that is superimposed in the expected resistance Contact noise - the result of mechanical contact between wiper and resistive surface - can cause up to 5 % of the total resistance. 2. Wire-wound Potentiometer - use a straight wire resistive element or coil wound resistive wire - The problem with wire wound potentiometers is the jumping of wiper between positions producing a logarithmic output signal 3. Polymer film or cermet type potentiometers - available for high precision and low noise applications LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - made up of conductive plastic resistive material. - have very less friction between the wiper and the surface and therefore less electrical noise, good resolution and longer life - vailable as both single turn and multi turn devices - used in high accuracy applications like joysticks, industrial robots etc. Capacitive Position Sensors - non-contact type of devices used for precision measurement of a target position if the target is conductive in nature, or used for measurement of thickness and density of a material if the target is non-conductive in nature - When used with conductive targets, they work irrespective of the material of the target as all conductors look same to a capacitive sensor - They are primarily used in measurement of linear displacement from a few millimeters to nanometers - When used with non-conductive targets, they are generally used in label detectors, coating thickness monitors, and paper and film thickness measuring units - make use of the electrical property conductance for measuring position. The ability to store electric charge by a body is capacitance Parallel plate capacitance - The most common device used to store charge in capacitive position sensor - The capacitance of a parallel plate capacitor is directly proportional to the surface area of the plates and dielectric constant, and inversely proportional to the distance between the plates - when the spacing between the plates is changed, there is a change in its capacitance and capacitive sensors make use of this property Capacitance Where εr is relative permittivity of dielectric εo is permittivity of free space A is the overlap area of plates And d is distance between the plates LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Capacitive sensors are calibrated to produce an output voltage corresponding to the change in distance between the probe and target which causes the capacitance to change Capacitive sensor probe Figure 10. Capacitive sensor probe and its components Sensing area – Application of potential Guard area – Prevents spreading of an electric field to areas on the target other than the defined sensing area and the target Figure 11. Sensing area of capacitive sensor The range of a sensing probe is directly proportional to the size of the sensing area LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited The maximum allowable gap between the probe and the target is approximately 40% of the diameter of the sensing area For non - conducting signals, The dielectric constant of the non- conductive target is the basis for the operation Figure 12. Sensing of Non conducting material Advantages 1. High resolution 2. Inexpensive 3. Not sensitive to the material of the target Disadvantages 1. Not suitable in conditions where the environment is dry or wet 2. The distance between the probe and the target is large Inductive Position Sensors - Are non-contact type of devices used for precision measurement of a target position if the target is conductive in nature - used to recognize any conducting metal target - make use of electromagnetic field that penetrates through the target - consists of an oscillator that generates a high frequency electromagnetic field. This field is radiating from the sensing face of the probe. - are independent of the material in the gap between the probe and the target LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - The material of the target is an important factor in inductive sensors. Materials like aluminum, steel and copper, each react differently to the sensor Figure 13. Inductive position sensor Important factor in inductive sensors 1. Material of the target Two types of target material for Inductive sensors 1. Ferrous Material - are magnetic in nature - include iron and most steel materials 2. Non Ferrous Material - Nonmagnetic - include zinc, aluminum, copper and brass 2. Size of the target - The effective area of electromagnetic field of the probe will vary from sensor to sensor - minimum requirement to have the cross sectional area of the target of at least 300 % of the probe’s coil diameter LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 14. Size of the target 3. Thickness of the target - an important factor as the electromagnetic field will penetrate the target and creates electrical currents - depends on the frequency of the signal which drives the probe and is inversely proportional to the frequency For a drive frequency of 1 MHz, the minimum thickness of some commonly used target materials is as follows: Iron—0.6 mm Stainless Steel—0.4 mm Copper—0.2 mm Aluminum—0.25 mm Brass—1.6 mm Advantages 1. Nanometer resolution 2. short response time 3. frequency responses of 80 KHz or more 4. repeat accuracy 5. immunity to environmental contaminants The output voltage and current of an inductive sensor is directly proportional to the distance between the surfaces of the sensor and the target LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Linear Variable Differential Transformer (LVDT) - a common type of electromechanical, high resolution, contact based linear position transducer - one of the best available, reliable and accurate methods for measuring linear distance - used in computerized manufacturing, machine tools, avionics and robotics Basic Construction - It basically consists of three coils wound on a hollow tube former, one forming the primary coil and the other two coils forming identical secondaries connected electrically together in series but 180o out of phase either side of the primary coil - A movable magnetic core is placed as shown in the figure. This magnetic core which is also called an armature controls the transfer of current between primary and secondary coils in the LVDT. The output of the LVDT is proportional to the position of the core. Figure 15. Cross sectional Area of LVDT Basic operation - When the primary coil is excited with an alternating current, a voltage is induced across secondary coils. The secondary coil voltage varies according to the position of the magnetic core between the coils which moves axially. The output electrical signal is equal to the difference between the voltages across the secondary windings. Therefore the output voltage is proportional to the linear mechanical movement of the magnetic core. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 16. A transformer style representation of the LVDT A small AC reference voltage called the “excitation signal” (2 – 20V rms, 2 – 20kHz) is applied to the primary winding which in turn induces an EMF signal into the two adjacent secondary windings If the soft iron magnetic core armature is exactly in the centre of the tube and the windings, “null position”, the two induced emf’s in the two LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited secondary windings cancel each other out as they are 180 o out of phase, so the resultant output voltage is zero The polarity of the output signal depends upon the direction and displacement of the moving core the output signal from this type of position sensor has both an amplitude that is a linear function of the cores displacement and a polarity that indicates direction of movement Typical application is as a pressure transducer were the pressure being measured pushes against a diaphragm to produce a force. Advantage of LVDT compared to Potentiometer 1. Its voltage output to displacement is excellent 2. very good accuracy 3. Good resolution 4. High sensitivity as well as frictionless operation 5. Sealed for use in hostile environments Inductive Proximity Sensor - low cost, solid state and non-contact based devices - basically used to detect metal objects which are both ferrous and non-ferrous in nature - Operate under the electrical principle of Faraday’s Law of inductance Four main component of inductive proximity sensor 1. Oscillator - produces the electromagnetic field 2. Coil - Generates the magnetic field 3. Detection circuit - detects any change in the field when an object enters it 4. Output circuit - produces the output signal, either with normally closed (NC) or normally open (NO) contacts Figure 17. Inductive Proximity Sensor LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Basic Operation When an alternating current is passed through the coil, it generates a high frequency magnetic field. If a metallic object comes near to this field, the inductance of the coil changes. Eddy currents induced in the object by the field will change the amplitude of the oscillations. The demodulator will detect the changes in amplitude and converts them into a DC signal. This DC signal trips the trigger and the output stage switches Sensing range : 0.1mm to 12mm Main application: 1. Industrial applications 2. Use in traffic light Main disadvantage: 1. They are “Omni-directional”, that is they will sense a metallic object either above, below or to the side of it 2. They do not detect non-metallic objects Hall Effect Based Magnetic Position Sensors - used to determine the position of objects by detecting the strength or direction or presence of magnetic fields generated from the Earth, electric currents, magnets and even brain wave activity - non-contact devices and are very important in many industries and navigation systems - Hall effect sensors are magnetic field sensor and can be used in sensing position, pressure, current, temperature and many more LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 18. General Hall Effect sensor Hall effect - states that, “when a current carrying conductor is placed in a magnetic field, a voltage is generated which is perpendicular to both current and magnetic field Eddy Current Based Position Sensor - non-contact based devices used to measure the position, displacement, oscillation and vibration of a conductive target - used in applications where high precision is required and the operating environment is harsh - work on the principle of magnetic induction Basic Operation - consists of a driver and a sensing coil. When an alternating current is passed through the coil, it generates an alternating magnetic field. When a target comes in contact with this field, a small current is induced in the target. These currents are called Eddy Currents. The Eddy current in the target will create a field which opposes the field of the sensor and resist the field. The distance between the LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited sensor and the target is the factor in interaction of the two magnetic fields. Hence, the output voltage is calibrated to the change in field interactions, which is dependent on the distance. The surface area of the target must be at least three times the diameter of the probe. Figure 19. Eddy Current Sensor Advantages 1. Less expensive 2. tolerance to harsh and dirty environment 3. smaller in size and not sensitive to the type of material used in the gap between the sensor and target Disadvantages 1. less useful in applications where high resolution is required and the gap between the sensor and target is large Rotary Encoder - an electromechanical device which converts angular motion to analog value or digital code - also called Shaft Encoder - provide value as the shaft or axle of the encoder rotates. An output signal is produced that is proportional to the angle of the rotation Two types of encoder 1. Incremental encoder - Output is in the form of a square wave and provides information about the motion of the shaft. This information is processed into speed, position, distance and RPM - provide output of pulse string that is proportional to the rotational displacement of the shaft i.e. it provides output only when the shaft of the encoder is rotated In applications where mechanical motion must be processed into digital information, the most popular choice of sensors is incremental encoders LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 20. Incremental encoder simplified structure Available in two types Single channel encoder - When the systems rotate in one direction - generally called Tachometers and provide only position and velocity information Quadrature” or “Sine wave” encoder - Has two output square waves commonly called channel A and channel B - Uses two photo detectors, slightly offset from each other by 90o thereby producing two separate sine and cosine output signals Figure 21. Quadrature channel encoder - The direction of rotation is determined by noting which channel produces an output first, either channel A or channel B giving two directions of rotation, A leads B or B leads A LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Main disadvantage of incremental encoders - They require external counters to determine the absolute angle of the shaft within a given rotation. If the power is momentarily shut off, or if the encoder misses a pulse due to noise or a dirty disc, the resulting angular information will produce an error Use of absolute position encoders is one way to overcome the disadvantage of incremental encoders 2. Absolute encoder - Output is in the form of absolute measure of position, i.e. they indicate the current position of the shaft. This makes them Angle Transducers - They provide a unique output code for every single position of rotation indicating both position and direction. The code can be gray code, excess gray code or natural binary code - Their coded disk consists of multiple concentric “tracks” of light and dark segments. Each track is independent with its own photo detector to simultaneously read a unique coded position value for each angle of movement. The number of tracks on the disk corresponds to the binary “bit”-resolution of the encoder Figure 22. Absolute encoder One main advantage of an absolute encoder is its non-volatile memory which retains the exact position of the encoder without the need to return to a “home” position if the power fails LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Main Application - in computer hard drives and CD/DVD drives were the absolute position of the drives read/write heads are monitored - in printers/plotters to accurately position the printing heads over the paper Optical Position Sensors - convert light signals into electric signals - similar to a photo resistor and measures the physical quantity and translates into a form that is readable by any appropriate instrument - can measure the following physical measurands: temperature, pressure, flow, liquid level, displacement, position, rotation, vibration, acceleration, force, velocity, strain, radiation, pH, magnetic field, electric field, acoustic field - includes three subsystems: a light source, a measuring device and an optical sensor. This is connected to an electrical trigger which reacts to changes in the signals in light sensor Fiber Optic Position Sensors - Use optical fibers as the sensing device - used to sense temperature, strain, pressure, displacement, velocity and acceleration - make use of retro reflectance of light inside an optical fiber because of the movement of the proximal mirror surface - immune to electromagnetic radiation, magnetic fields, lightning and many other harsh environmental conditions - used in long distance position sensing Fiber optic sensors are of two types: intrinsic and extrinsic sensors intrinsic sensors - the measurand modulates the transmission properties of sensing optical fiber. The properties are intensity, polarization, phase, etc. Extrinsic sensor - the modulation takes place outside the fiber. Here the optical fiber just acts as a conduit to transport light from and to the sensor head The advantages of fiber optic position sensors are: 1. Immune to electromagnetic radiation. 2. Consists of electrically insulating material. 3. Wide temperature range. 4. Ability to multiplex signals. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Temperature Sensors Temperature - most widely sensed parameter of all physical parameters because of its significance on materials and processes at the molecular level - a specific degree of hotness or coldness as referenced to a specific scale - also defined as the amount of heat energy in a system or object. Heat energy is directly related to molecular energy: molecular energy is greater when the heat energy is higher Temperature sensor - monitor the changes that take place in materials or objects as their temperature changes Types of temperature sensor 1. Contact based - the sensor will be in physical contact with the object that is being sensed 2. Non – contact based - the sensor interprets the radiant energy of a heat source. The radiant energy is the form of energy emitted in the infrared portion of the electromagnetic spectrum. - Non-reflective solids and liquids can be monitored using non-contact technique Can be subdivided into three families 1. Electromechanical 2. Resistive 3. Electronic Figure 23. Temperature sensor Categories LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Electromechanical Sensors 1. Bi-metal Thermostats or Bi-metallic Strips(Thermostat - contact type electro-mechanical sensor used to measure the temperature inside home - contact type electro-mechanical temperature sensor or switch, that basically consists of two different metals such as nickel, copper, tungsten or aluminum etc, that are bonded together to form a Bi- metallic strip - The different linear expansion rates of the two dissimilar metals produces a mechanical bending movement when the strip is subjected to heat - can be used itself as an electrical switch or as a mechanical way of operating an electrical switch in thermostatic controls - used extensively to control hot water heating elements in boilers, furnaces, hot water storage tanks as well as in vehicle radiator cooling systems Thermostat Basic Principle - The basic principle of working is Thermal Expansion to switch an electrical circuit ON and OFF. It consists of two different metals like nickel, copper, tungsten or aluminum. Combination of any two metals forms a compound strip. They are bonded together using heat and pressure. This is called Bi-metallic strip. Two metals has different expansion rate. Therefore, when heat is applied on the strip, it undergoes a mechanical bending movement. Bi-metallic strip operates like a bridge, which helps to connect or disconnect the electric circuit of the heating or cooling system inside the house or industry Figure 24. Working Principle of Thermostat LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Two types of Bi-metallic strip 1. Snap action type - Produce an instantaneous “ON/OFF” or “OFF/ON” type action on the electrical contacts at a set temperature point - Commonly used in our homes for controlling the temperature set point of ovens, irons, immersion hot water tanks and they can also be found on walls to control the domestic heating system - Main disadvantage is the larger hysteresis range from when the electrical contacts open until when they close again. (Ex: It may be set to 20oC but may not open until 22oC or close again until 18oC) 2. Creep-action type - Gradually change their position as the temperature changes - consist of a bi-metallic coil or spiral that slowly unwinds or coils-up as the temperature changes - more sensitive to temperature changes than the standard snap ON/OFF types as the strip is longer and thinner making them ideal for use in temperature gauges and dials etc 2. Bulb and Capillary Thermostats - They use capillary action of expanding or contracting of a fluid to make or break electrical contact. Resistive Sensors 1. Thermistor - thermally sensitive resistors - the electrical resistance changes according to their temperature - They are made of a combination of two or three metal oxides with zinc oxide among one of them. This combination is inserted in a ceramic base which is an insulator Thermistors are available in two types based on temperature coefficient 1. Positive temperature coefficient thermistors - Resistance and temperature are directly proportional to each other 2. Negative temperature coefficient thermistors - resistance and temperature are inversely proportional to each other i.e. the resistance decreases as the temperature rises - provide a higher degree of sensitivity and are available in small configurations for rapid thermal response Thermistor’s are non-linear devices and their standard resistance values at room temperature is different between different thermistor’s, which is due mainly to the semiconductor materials they are made from. The Thermistor, have an exponential change with temperature and therefore have a Beta temperature constant ( β ) which can be used to calculate its resistance for any given temperature point LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited If the resistance of a thermistor is known at a temperature θ2, then the resistance at temperature θ1 can be calculated using the following equation: Where B is Thermistor constant θ1 and θ2 are temperatures in Kelvin R1 and R2 are resistances. The range of temperature for negative temperature coefficient thermistors is from -1500C to 2000C. Some negative temperature coefficient thermistors can withstand a temperature up to 6000C Advantages 1. Low Cost 2. Fast response 3. Small size 4. High resistance Disadvantages 1. Self – heating 2. No resistance standards 3. Requirement of additional circuitry to control application loads 4. Low temperature exposure than thermocouples Resistive Temperature Devices (RTD) - changes to measure and control temperature - Consists sensing element, connecting wires and measuring instrument. The connecting wires are used between the sensing element and measuring instrument and a support is used for positioning the element in the process LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 25. RTD Element Construction - Also available are thin-film RTD’s. These devices have a thin film of platinum paste is deposited onto a white ceramic substrate - have positive temperature coefficients (PTC) but unlike the thermistor their output is extremely linear producing very accurate measurements of temperature - They have very poor thermal sensitivity, that is a change in temperature only produces a very small output change for example, 1Ω/oC Platinum Resistance Thermometer or PRT - Most common type of RTD - Commonly available Pt100 sensor, which has a standard resistance value of 100Ω at 0oC - Downside is that Platinum is expensive and one of the main disadvantages of this type of device is its cost Typical RTD resistance: - 100Ω at 0oC, increasing to about 140Ω at 100oC with an operating temperature range of between -200 to +600oC - RTD is usually connected to a wheatstone bridge network to avoid error in the readings cause by variation of resistance due to self heat of the resistive wires as the current flows through it Electronic Sensors Thermocouples - Most commonly used type of all the temperature sensor types - Popular due to its simplicity, ease of use and their speed of response to changes in temperature, due mainly to their small size - Have the widest temperature range of all the temperature sensors from below -200oC to well over 2000oC - Basically consists of two junctions of dissimilar metals, such as copper and constantan that are welded or crimped together. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - One junction is kept at a constant temperature called the reference (Cold) junction, while the other the measuring (Hot) junction. When the two junctions are at different temperatures, a voltage is developed across the junction which is used to measure the temperature sensor Figure 26. Thermocouple Principles of a Thermocouple It works based on three effects 1. Seebeck Effect: When two dissimilar materials at different temperatures are connected together and heat is provided to any one of the metal, there will be flow of electron from hot metal to cold metal. This electron movement will result in generation of current in the circuit. The temperature difference between the metals will induce a potential difference between them. 2. Peltier Effect: The reverse of Seebeck effect is the Peltier Effect. It states that when a potential difference is applied between two metals, it creates a temperature difference between the connected metals. 3. Thomson’S Effect: Whenever two different metals are combined together, two junctions will be created. At this condition, due to temperature difference between two metals a voltage will be generated across the conductor. To calculate the EMF, thermocouples make use of Seebeck effect. According to Seebeck effect, the EMF in a thermocouple is given by the following equation LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Where: a, b and c are constants for the types of metals used in the thermocouple and θ is the temperature difference between them If the cold junction is maintained at 0 0C, the EMF is E = αT2 + βT Where α and β are the measured constants for the pair of metals and T is the difference in temperature Figure 27. Working of a thermocouple Thermocouple types 1. Type S - it uses pure Platinum as one metal and an alloy of 90% Platinum, 10% Rhodium as other metal - recommended for high temperatures and the range of temperature is 00C to 14000C and must be protected with a non-metallic tube with ceramic insulators 2. Type R - It uses pure Platinum as one metal and an alloy of 87% Platinum, 13% Rhodium as other metal - It is similar to Type S but Type R is used for industrial purpose and Type S is used for laboratory purpose 3. Type J - It is made up of iron as one metal and an alloy of Copper – Nickel as other metal LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - The temperature range is 00C to 8000C - suitable for vacuum or inert atmospheres - At higher temperatures, a heavy gauge wire is recommended as Iron oxidizes rapidly above 5400C and oxidizing atmospheres will reduce life 4. Type K - It uses alloys of Nickel – Chromium and Nickel – Aluminum - The temperature range of Type K thermocouple is 00C – 11000C - Since iron is not used as one of the metals, they are suitable for continuous oxidizing atmospheres mostly above 5400C - When exposed to Sulfur, type K thermocouple might be subject to failure - Between the temperature of 8160C to 10380C and at low oxygen concentrations, the preferential oxidation of Chromium causes green rot and a large negative calibration drift. To prevent this scenario, ventilation or sealing of protection tubes can be done 5. Type E - This type uses Nickel – Chromium and Copper – Nickel alloys as thermocouple - These types are recommended for continuous oxidizing atmospheres - They provide the highest thermo-electric output of all available thermocouples. The range of temperatures are 00C to 8000C 6. Type T - It uses Copper as one of the metals and an alloy of Copper – Nickel as other metal - Usable in vacuum, oxidizing, inert atmospheres and also works in subzero temperatures - The temperature range is -2000C to 4000C. It is resistant to corrosion in moist atmospheres 7. Type B - similar to Types R and S but with lower output 8. Type N - Use Nicrosil and Nisil alloy - Temperature range is 00 to 12500C - used as a substitute to Type K where it has a shorter life and stability issues LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Three Types of junction styles 1. Grounded Junction - in order to protect the hot or measurement junction, it is welded to the inside of a protective metal sheath - This might affect the thermal response, but makes it susceptible to electromagnetic interference 2. Ungrounded junction - a thermally conductive material that is used to electrically insulate the hot junction from its protective metal sheath - This isolates the junction from electromagnetic interference, but increases thermal lag 3. Exposed junction - has the fastest response time - In this junction type, in order to form the hot junction, the sensing tip is made from two dissimilar wires joined by soldering, and welding Advantages 1. Small size 2. Rapid temperature response 3. Inexpensive 4. Wider temperature range 5. Durable to vibrations and shock Disadvantages 1. Less stability at higher temperature 2. Requirement of extra protections from corrosions 3. Requirement of additional circuitry to control application loads and the use of special extension wires Other temperature Sensors Silicon Sensors Infrared Pyrometer Resistance thermometers Silicon Bandgap Temperature Sensors Light 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 - Commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons) LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Actuators - convert an electrical signal into a corresponding physical quantity such as movement, force, sound etc Two Classification of actuators 1. Binary actuator – Have only two stable states. Ex. Relay 2. Continuous Actuator – Have many possible states. Ex. Motor Common types of actuator 1. Electrical Relays 2. Motor 3. Lights 4. Loudspeaker Electrical Relays - generally refers to a device that provides an electrical connection between two or more points in response to the application of a control signal - are basically electrically operated switches that come in many shapes, sizes and power ratings suitable for all types of applications Contactors – Larger power relays used for mains voltage or high current switching applications Two types of Electrical relays 1. Electromechanical Relays - mechanical action relays 2. Solid state Relays – Relays which use semiconductor transistors, thyristors, triacs, etc, as their switching device Electromechanical relays - electro-magnetic devices that convert a magnetic flux generated by the application of a low voltage electrical control signal either AC or DC across the relay terminals, into a pulling mechanical force which operates the electrical contacts within the relay - most common form of electromechanical relay consist of an energizing coil called the “primary circuit” wound around a permeable iron core LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 28. Electromechanical Relay Construction State of Electrical contacts of relay 1. Normally Open – Make contact - The contacts are closed only when the field current is “ON” and the switch contacts are pulled towards the inductive coil 2. Normally Closed - Break contacts - the contacts are permanently closed when the field current is “OFF” as the switch contacts return to their normal position On resistance – Resistance of contact in the relay when they are closed - Generally less than 0.2Ω when the tips are new and clean - Increases when the contact tips begin to wear which may produce arcing across the contacts and eventually damage the circuit it is controlling - Used a variety of silver based alloys in the contact tip to extend the life span and reduce the On resistance LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Electrical Relay Contact Tip Material 1. Ag (fine silver) - Electrical and thermal conductivity are the highest of all the metals. - Exhibits low contact resistance, is inexpensive and widely used. - Contacts tarnish easily through sulphurisation influence. 2. AgCu (silver copper) - Known as “Hard silver” contacts and have better wear resistance and less - tendency to arc and weld, but slightly higher contact resistance. 3. AgCdO (silver cadmium oxide) - Very little tendency to arc and weld, good wear resistance and arc extinguishing properties. 4. AgW (silver tungsten) - Hardness and melting point are high, arc resistance is excellent. - Not a precious metal. - High contact pressure is required to reduce resistance. - Contact resistance is relatively high, and resistance to corrosion is poor. 5. AgNi (silver nickel) - Equals the electrical conductivity of silver, excellent arc resistance. 6. AgPd (silver palladium) - Low contact wear, greater hardness. - Expensive. 7. Platinum, Gold and Silver Alloys - Excellent corrosion resistance, used mainly for low-current circuits. RC Snubber Network - Resistor-Capacitor network used to extend the life of relay tips by reducing the amount of arcing generated as they open LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 29. Electrical Relay Snubber Circuit Electrical Relay Contact Types Pole – Switch Contact Throw – Connection of the switch SPST – Single Pole Single Throw SPDT – Single Pole Double Throw DPST – Double Pole Single Throw DPDT – Double Pole Double Throw Figure 30. Electrical Relay Contact Configurations As the current flows through the coil a self induced magnetic field is generated around it. When the current in the coil is turned “OFF”, a large back emf (electromotive force) voltage is produced as the magnetic flux LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited collapses within the coil (transformer theory). This induced reverse voltage value may be very high in comparison to the switching voltage, and may damage any semiconductor device such as a transistor, FET or micro-controller used to operate the relay coil One way of preventing damage to the transistor or any switching semiconductor device, is to connect a reverse biased diode across the relay coil. Diode use in this application is also called Flywheel diode other devices used for protection include RC Snubber Networks, Metal Oxide Varistors or MOV and Zener Diodes Figure 31. Relay circuit with protection Main disadvantage of using electromechanical relay 1. Slow response in switching time due to physical movement of metal contacts 2. Moving parts will wear out and fail 3. Contact resistance through the constant arcing and erosion may make the relay unusable and shortens its life 4. electrically noisy with the contacts suffering from contact bounce which may affect any electronic circuits to which they are connected Solid State Relay - solid state contactless, pure electronic relay - Has no moving parts within its design as the mechanical contacts have been replaced by power transistors, thyristors or triac’s LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited - The electrical separation between the input control signal and the output load voltage is accomplished with the aid of an opto-coupler - must be mounted onto suitable heatsinks to prevent the output switching semiconductor device from over heating Figure 32. Solid State Relay Circuit Advantage over Electromechanical relay 1. High degree of reliability 2. Longer life span 3. Reduced electromagnetic interference (EMI), (no arcing contacts or magnetic fields) 4. Much faster almost instant response time 5. Input control power requirements of the solid state relay are generally low 6. Compatible with most IC logic families without the need for additional buffers, drivers or amplifiers Linear Solenoid Actuator - Converts electrical energy into a mechanical pushing or pulling force or motion - Consist of an electrical coil wound around a cylindrical tube with a ferro-magnetic actuator or “plunger” that is free to move or slide “IN” and “OUT” of the coils body - Can be used to electrically open doors and latches, open or close valves, move and operate robotic limbs and mechanisms, and even actuate electrical switches just by energising its coil Two kinds of Solenoid 1. Linear electromechanical Actuator 2. Rotary Solenoid LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Basic principle When an electrical current is passed through the coils windings, it behaves like an electromagnet and the plunger, which is located inside the coil, is attracted towards the centre of the coil by the magnetic flux setup within the coils body, which in turn compresses a small spring attached to one end of the plunger. The force and speed of the plungers movement is determined by the strength of the magnetic flux generated within the coil. When the supply current is turned “OFF” (de-energised) the electromagnetic field generated previously by the coil collapses and the energy stored in the compressed spring forces the plunger back out to its original rest position. This back and forth movement of the plunger is known as the solenoids “Stroke”, in other words the maximum distance the plunger can travel in either an “IN” or an “OUT” direction, for example, 0 – 30mm. Linear Solenoid Construction Linear solenoids are available in two basic configurations called a “Pull- type” as it pulls the connected load towards itself when energised, and the “Push-type” that act in the opposite direction pushing it away from itself when energised. Both push and pull types are generally constructed the same with the difference being in the location of the return spring and design of the plunger Figure 33. Linear Solenoid Construction Common applications Electronically activated door locks Pneumatic or hydraulic control valves Robotics Automotive engine management Irrigation valves LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Rotary Solenoids - Produce an angular or rotary motion from a neutral position in either clockwise, anti-clockwise or in both directions (bi-directional) - Can be used to replace small DC motors or stepper motors were the angular movement is very small with the angle of rotation being the angle moved from the start to the end position - Produce a rotational movement when either energised, de-energised, or a change in the polarity of an electromagnetic field alters the position of a permanent magnet rotor - Consists of an electrical coil wound around a steel frame with a magnetic disk connected to an output shaft positioned above the coil Common Applications Vending or gaming machines Valve control Camera shutter with special high speed Low power or variable positioning solenoids with high force or torque are available such as those used in dot matrix printers, typewriters, automatic machines or automotive applications Solenoid Switching Figure 34. Solenoid Circuit DC motors - Electromechanical devices which use the interaction of magnetic fields and conductors to convert the electrical energy into rotary mechanical energy LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 35. DC motor construction Sound Transducer - Use electrical energy to create mechanical vibrations to disturb the surrounding air producing sound whether of an audible or inaudible frequency - Include both input sensors, that convert sound into and electrical signal such as a microphone, and output actuators that convert the electrical signals back into sound such as a loudspeaker Microphone sound transducer that can be classed as a “sound sensor” produces an electrical analogue output signal which is proportional to the “acoustic” sound wave acting upon its flexible diaphragm Common types of microphone 1. Dynamic 2. Electret Condenser 3. Ribbon 4. Piezo-Electric Crystal Dynamic Moving-coil Microphone Sound Transducer - It is a moving coil type microphone which uses electromagnetic induction to convert the sound waves into an electrical signal - It has a very small coil of thin wire suspended within the magnetic field of a permanent magnet. As the sound wave hits the flexible diaphragm, the diaphragm moves back and forth in response to the sound pressure acting upon it causing the attached coil of wire to move within the magnetic field of the magnet LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 36. Basic construction of Microphone Loudspeaker - audio sound transducers that are classed as “sound actuators” and are the exact opposite of microphones - use to convert complex electrical analogue signals into sound waves being as close to the original input signal as possible Common types 1. Moving coil 2. Electrostatic 3. Iso dynamic 4. Piezo - electric Moving coil loudspeaker A coil of fine wire, called the “speech or voice coil”, is suspended within a very strong magnetic field, and is attached to a paper or Mylar cone, called a “diaphragm” which itself is suspended at its edges to a metal frame or chassis. Then unlike the microphone which is pressure sensitive input device, this type of sound transducer can be classed as a pressure generating output device LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Figure 37. Moving coil loudspeaker Nominal impedance of loudspeaker – 4 to 16 Ω LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Performance Tasks PT 1 Problem Solving: 1. What will be the wavelength of light in a material if the energy contained in a photon is equivalent to 1 eV? 2. A certain potentiometer position sensor in the figure below is detected to have 75% near the maximum value it can give. Determine the output voltage PT 2 1. Design a simple circuit system that contains a sensor and a transducer. Explain how it works. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING  Republic of the Philippines Laguna State Polytechnic University Province of Laguna ISO 9001:2015 Certified Level I Institutionally Accredited Learning Resources 1. FLOYD, T.L. (2005). ELECTRONIC DEVICES 7TH EDITION. USA: PEARSON PRENTICE HALL 2. BOYLEST, R.L. & NASHELSKY, L. (2013). ELECTRONIC DEVICES AND CIRCUITS THEORY 11TH EDITION. USA: PEARSON 3. https://www.electronicshub.org/sensors-and-transducers-introduction/ 4. https://www.electronics-tutorials.ws/io/io_1.html Intellectual Property This module is for educational purpose only. Under section Sec. 185 of RA 8293, which states, “The fair use of a copyrighted work for criticism, comment, news reporting, teaching including multiple copies for classroom use, scholarship, research, and similar purposes is not an infringement of copyright.” The unauthorized reproduction, use, and dissemination of this module without joint consent of the authors is strictly prohibited and shall be prosecuted to the full extent of the law, including appropriate administrative sanctions, civil, and criminal. LSPU SELF-PACED LEARNING MODULE: TECHNOLOGY FOR TEACHING AND LEARNING