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micro manit.pptx

  2. Data Acquisition Systems
  3. What is a Data Acquisition System? • A data acquisition system is a system that comprises sensors, measurement devices, and a computer. A data acquisition system is used for processing acquired data, which involves collecting the information required to understand electrical or physical phenomena. • The reason for measuring and recording the electrical and physical phenomena using a data acquisition system is to enable further analysis. A data acquisition system uses software to perform its functions and it is capable of quickly processing and storing data in many ways. Data acquisition systems can capture data from an actual system and store the data in a simple format that is easily retrievable for further engineering or scientific review. • Data acquisition systems are either handheld, or they can be remotely operated. Handheld data acquisition systems are used when there is a requirement for taking readings of a specimen which can be physically interacted with. When direct human interaction with an object is not possible or necessary, this is when remote data acquisition systems are used to take remote DAQ (data acquisition) measurements.
  4. Basic Components of a Data Acquisition System
  5. Sensors • Sensors or transducers serve the purpose of interacting with the subject measured. They interact with the subject either directly or indirectly, or as defined in other words, contact or non-contact. These tools convert the physical values to produce an output of electrical signals. • The sensors utilized by DAQ systems are high-quality sensors that are capable of giving accurate readings with minimal or no noise.
  6. Transmission/Signal Conditioners • The electrical signals obtained from the sensors may contain noise or other interference and need modification; they could not be used directly as is. The signals might also be weak to a point where the data acquisition system cannot measure them. Hence additional circuitry is utilized for optimizing the signals. This additional circuitry is known as a signal conditioner. Signal conditioning then is the process of optimizing the signals.
  7. Data Acquisition Hardware • Data acquisition hardware is the hardware that is connected between the sensors and the computer. This hardware is either connected to the computer employing a USB port or through the PCI-express ports that are found on the motherboard. The data acquisition hardware serves to take in the signals from the sensors and then convert them into digital signals that are readable by the computer. This is the function that DAQ hardware performs.
  8. Analog-to-Digital Converters • This component of the DAQ system serves to convert analog signals into digital signals. This component is at the core of all data acquisition systems. This chip serves to take data from the environment and convert it into separate levels that can be interpreted by a processor. These distinct levels correspond to the smallest detectable change that can be found in the measured signal. Digital-to-Analog Converters • The function of this component of a DAQ system is to provide support for inputting, as well as outputting, binary signals Single-Ended Input Converters • This component has the function of providing support for taking input from single-ended wire. Some types of DAQ hardware are standalone, capable of operating on their own without the requirement of a connection to a computer. This is possible through the use of a processor as well as a computing unit that is embedded within the hardware of the data acquisition system. Standalone data acquisition hardware is capable of helping users with real-time data representation. Computers • The computer is the end piece of a DAQ chain. The computer’s function is to gather all data that comes through the DAQ hardware for further analysis. However, it is not enough to simply connect the DAQ hardware to a computer in order to make sense of the data collected. DAQ software that uses data from the DAQ hardware is still required for creating readable and meaningful results. This data acquisition software acts as the layer between the DAQ hardware and the user. With the data that is collected from the DAQ, computers are critical to performing higher-order computations.
  9. Applications of Data Acquisition Systems Electronics • Data acquisition systems are utilized in the electronics industry. They are utilized in the testing of many variables that are involved in the design of electronics like heat production, resistance, conductivity, magnetics, etc. Automotive Industry • Data acquisition devices are utilized in automotive manufacturing for testing the quality of the parts that are manufactured. Industrial Machines • Industrial machines are created to perform multiple times. Therefore, repeatability is of critical importance. Data acquisition systems are often utilized for testing these machines for their tolerance to repetitive forces. Non-Destructive Testing • Data acquisition systems are utilized in the non-destructive testing of structures, geology, seismology, ultrasonic measurements, as well as with the analysis of acoustic emission phenomena.
  10. Imaging • Data acquisition systems are used for the quality testing of imaging equipment like a photographic lens or video camera, as well as with scientific equipment such as scanners, and microscopes. Laser Technology • Data acquisition systems are utilized in laser technology to test laser performance, light intensity, and color Sonar-Radar • Data acquisition systems use remote sensing technologies within radar and sonar applications to calculate their efficiency and effectiveness
  11. Industrial Machines • Industrial machines are created to perform multiple times. Therefore, repeatability is of critical importance. Data acquisition systems are often utilized for testing these machines for their tolerance to repetitive forces. Non-Destructive Testing • Data acquisition systems are utilized in the non-destructive testing of structures, geology, seismology, ultrasonic measurements, as well as with the analysis of acoustic emission phenomena.
  12. Microprocessor and microcontroller
  13. Microprocessor
  14. Introduction • The microprocessor alsoknown asthe central processing unit, is the brain of all computers and manyhousehold and electronic devices. Multiple microprocessors, working together, are the "hearts" of datacenters, super-computers, communications products, and other digital devices.
  15. History ●Fairchild Semiconductors (founded in 1957) invented the first IC in 1959. ●In 1968, Robert Noyce, Gordan Moore, Andrew Grove resigned from Fairchild Semiconductors. ●They founded their own company Intel (Integrated Electronics). ●The first microprocessor invented wasof 4-bit, after that 8- bit,16-bit,.32-bit &64-bit are founded
  16. History ●4-bit microprocessor • Intel 4004 • Intel 4040 ➢8-bit microprocessor • Intel 8008 • Intel 8080 • Intel 8085 ➢16-bit microprocessor • Intel 8086 • Intel 8088 • Intel 80186 &80188
  17. History • Intel 80286 ➢32-bit microprocessor • Intel 80386 • Intel 80486 • Intel pentium • Intel pentium pro • Intel pentium II • Intel pentium II xeon • Intel pentium III • Intel pentium IV • Intel dual core
  18. History ➢64-bit microprocessors • Intel core 2 • Intel core i7 • Intel core i5 • Intel core i3
  19. Microprocessor (MPU) ●MPU (CPU) ●Read instructions ●Process binary data
  20. Memory ●Storage Device ●Addresses ●Registers ●Major Categories ●Read/Write Memory (R/W) ●Read-only-Memory (ROM) D7 D0
  21. Input/Output (I/O) ●Input Devices ●Switches and Keypads ●Provide binary information to the MPU ●Output devices ●LEDs and LCDs ●Receive binary information from the MPU
  22. Microprocessor Architecture ●The MPUcommunicates with Memory and I/ O using the System Bus ●Address bus ●Unidirectional ●Memory and I/O Addresses ●Data bus ●Bidirectional ●Transfers Binary Data and Instructions ●Control lines ●Read andWrite timing signals
  23. Microprocessor – Basic concept CPU contains CCU ALU data registers and pointer registers ADDRESS BUS 32-bit / 64-bit wide CONTROL BUS Timing signals, ready signals, interrupts etc DATA BUS – bidirectional 8-bit / 16-bit / 32-bit / 128-bit Microprocessor, by-itself, completely useless – must have external peripherals to Interact with outside world
  24. Microcontroller
  25. Micro controller ●A self-contained system in which aprocessor, support, memory, and input/ output (I/ O) are all contained in asingle package. ●A small computer system on asingle IC
  26. History of Microcontroller ●First used in 1975(Intel 8048) ●The introduction of EEPROMin 1993, allowed microcontrollers to be electrically erased ●The same year,Atmel introduced the first microcontroller using Flash memory.
  27. Microcontroller
  28. Types of microcontroller
  29. Basic Features of Microcontroller ●Processor reset ●Device clocking ●Central processor ●Program and Variable Memory (RAM) ●I/ O pins ●Instruction cycle timers
  30. More Sophisticated Features ●Built-in monitor/ debugger program ●Interrupt capability ●Analog I/ O (PWM and variable dc I/ O ●Serial I/ O (synchronous, asynchronous) ●Parallel I/ O (including direct interface to amaster processor ●External memory interface
  31. Basic microcontroller architecture (1/3)
  32. Basic microcontroller architecture (2/3) ●Memory ●RAM ●ROM ●Store data and code ●CPU ●Mathematical and logical operation ●Memory units are called Register
  33. Basic microcontroller architecture (3/3) • BUS – Group of 8,16 or more wires – Three type, address bus, data bus and control bus • Input-output unit – portA, port B, port C … … – Input, output and bidirectional ports • Serial communication • Timer unit • Watchdog – Automatic reset to prevent stall • Analogto Digital Converter (ADC)
  34. Processor Architecture ●CISC ➢Large amount of instructions each carrying out adifferent permutation of the same operation ➢Functionality of the instructions is more dependent upon the processor’s designer. ●RISC ➢Fundamental set of instructions ➢More control for users to design their own operations
  35. Von Neumann Architecture
  36. Processor Architecture ●Princeton (Van Neumann) architecture ➢Common memory for program and data ➢Simple chip design ➢Execution of an instruction can take multiple cycles
  37. Processor Architecture ●Princeton architecture example Movacc, reg Cycle 1 Cycle 2 Read instruction Read data out of Ram and put into Acc
  38. Processor Architecture ●Harvard architecture ➢Separate memory space program and data ➢Instructions are executed in one cycle ➢Easier timing of loops and delays
  39. Harvard Architecture
  40. Processor Architecture ●Harvard architecture example Movacc, reg Cycle 1 Execute previous instruction Cycle 2 Read “move acc, reg” Execute “move acc, reg” instruction
  41. Block diagram of Microcontroller
  42. Memory ●The memory in a computer system stores the data and instructions of the programs. Adress decoder Storage Area Adress bus Data bus Other signals (Vcc,Gnd, CS, etc.)
  43. Microcontrollers Memory Types ●VariableArea (RAM) ●Control Store (ROM) ●Program Counter Stack ●I/ O Space (Hardware interface Registers)
  44. I/O Space - Memory Mapped I/ O Versus Programmed I/ O ●Programmed I/O Special instructions such as IN and OUT are used to transfer data between aCPU register and an external device. ●Memory Mapped I/O Standard instructions are used to transfer data between a CPU register and an external device. I/O ports appear as memory addresses.
  45. Interrupts ● ● ● Instruction support for interrupts Internal CPU handling of interrupts Interruptible instructions
  46. Instruction support for interrupts ●Processors provide two instructions, enable priority interrupt (EPI) and for disable priority interrupt (DPI). ●These are atomic instructions that are used for many purposes, such as buffering, within interrupt handlers, and for parameter passing.
  47. Internal CPU handling of interrupts Step 1: finish the currently executing macroinstruction. Step 2: save the contents of the program counter to the interrupt return location. Step 3: load the address held in the interrupt handler location into the program counter. Resume the fetch and execute sequence. Single interrupt support
  48. Internal CPU handling of interrupts Step 1: complete the currently executing instruction. Step 2: save the contents of PC to interrupt return location i. Step 3: load the address held in interrupt handler location i into the PC. Resume the fetch-execute cycle. Multiple interrupt support
  49. Interruptible instructions ●In rare instances individuation macroinstruction mayneed to be interruptible. ●This might be the case where the instruction takes agreat deal of time to complete. E.g. amemory to memory instruction that moves large amounts of data. ●In most cases, such an instruction should be interruptible between blocks to reduce interrupt latency.However, interrupting this particular instruction could cause data integrity problems.
  50. Advantages of Microcontroller over Microprocessor ●Pin count down ●Design time down, Board layout size down ●Upgrade path easier – matching between peripherals for speed ●Cost down – bulk purchases ●Reliability up ●Common software / hardware design environment available from manufacturer
  51. Issues when using microcontroller ● Twotypesofmemory–speedissueswhenusing ●On-chip – fast, easy to access, “almost like a register”, limited amount of on-chip memory available ●Off-chip – slower ●Use on-chip memory in a“cache” mode (copy off-chip data to on-chip when processing data, then copy back) ● Externalcomponentsstillthere ●E.g. Video CODECs – need to use DMA– Direct MemoryAccess– so that the controller can get on with the “processing”and let something else worry about moving data in and out of the chip ● Realtimeenvironment ●Event driven – can’t WAITfor a device to become ready, can’t POLLto see if device is ready, interrupt handling is key ● All these resources are “power hungry” and compete for resources (data busses etc) – special features
  52. Difference between microprocessor & microcontroller Microprocessor Microcontroller Contains ALU, general purpose register, stack pointer, programme counter, clock timing & interrupt circuit It hastoo manyinstructions to movethe data between CPU&memory It hasone or two bit handlinginstruction Accesstime for memory &I/O devices ismore Microprocessor basedsystem requires more hardware More flexible in design point of view It hassingle memory mapfor data &code Lessnumber ofpins are malfunctioned Contains the circuitry ofmicroprocessor &in addition it hasbuilt in ROM, I/ Odevices, timer &counter It hasone or two instruction to movethe data between CPU&memory It hasmanybit handling instruction Lessaccesstime for built in memory &I/O devices Microcontroller basedsystem requires less hardware,reducing PCBsize&increasing the reliability Lessflexible in designpoint ofview It hasseparate memory map for data &code More number of pins are malfunctioned Microprocessor Microcontroller
  53. Electric Drive Block Diagram, Types and Applications
  54. The first electric drive was invented in 1838 by B.S.Iakobi in Russia. He tested a DC motor which is supplied from a battery to push a boat. Although, the application of electric drive in industrial can happen after so many years like in 1870. At present, this can be observed almost everywhere. We know that the speed of an electrical machine(motor or generator) can be controlled by the source current’s frequency as well as the applied voltage. Although, the revolution speed of a machine can also be controlled accurately by applying the electric drive concept. The main benefit of this concept is too controlling the motion can be optimized simply using the drive. What is an Electric Drive? • An Electric Drive can be defined as, a system which is used to control the movement of an electrical machine. This drive employs a prime mover such as a petrol engine, otherwise diesel, steam turbines otherwise gas, electrical & hydraulic motors like a main source of energy. These prime movers will supply the mechanical energy toward the drive for controlling motion An electric drive can be built with an electric drive motor as well as a complicated control system to control the motor’s rotation shaft. At present, the controlling of this can be done simply using the software. Thus, the controlling turns into more accurate & this drive concept also offers the ease of utilizing
  55. The types of electrical drives are two such as a standard inverter as well as a servo drive. A standard inverter drive is used to control the torque & speed. A servo drive is used to control the torque as well as speed, and also components of the positioning machine utilized within applications that need difficult motion Block Diagram of Electric Drive • The block diagram of an electric drive is shown below, and the load in the diagram signifies different kinds of equipment which can be built with an electric motor such as washing machine, pumps, fans, etc. The electric drive can be built with source, power modulator, motor, load, sensing unit, control unit, an input command.
  56. Power Source • The power source in the above block diagram offers the necessary energy for the system. And both the converter and the motor interfaces by the power source to provide changeable voltage, frequency and current to the motor. Power Modulator • This modulator can be used to control the o/p power of the supply. The power controlling of the motor can be done in such a way that the electrical motor sends out the speed-torque feature which is necessary with the load. During the temporary operations, the extreme current will be drawn from the power source. • The drawn current from the power source may excess it otherwise can cause a voltage drop. Therefore the power modulator limits the motor current as well as the source. • The power modulator can change the energy based on the motor requirement. For instance, if the basis is direct current & an induction motor can be used after that power modulator changes the direct current into alternating current. And it also chooses the motor’s mode of operation like braking otherwise motoring. Load • The mechanical load can be decided by the environment of the industrial process & the power source can be decided by an available source at the place. However, we can choose the other electric components namely electric motor, controller, & converter.
  57. Control Unit • The control unit is mainly used to control the power modulator, and this modulator can operate at power levels as well as small voltage. And it also works the power modulator as preferred. This unit produces the rules for the safety of the motor as well as power modulator. The i/p control signal regulates the drive’s working point from i/p toward the control unit. Sensing Unit • The sensing unit in the block diagram is used to sense the particular drive factor such as speed, motor current. This unit is mainly used for the operation of closed loop otherwise protection. Motor • The electric motor intended for the specific application can be chosen by believing various features such as price, reaching the level of power & performance necessary by the load throughout the stable state as well as active operations. Types of electrical drives: • Servomotor • Stepper Motor • DC Motor
  58. Characteristics of Electrical drives: The electric drives generally require reduction gears of high ratios. The high-gear ratio linearizes the system dynamics and reduces the coupling effects. This is an added advantage of the electric drives but at the cost of increased joint friction, elasticity and backlash. On the author hand use of hydraulic or pneumatic actuators to directly drive the joint minimizes the drawbacks due to friction, elasticity, and backlash. 1) Easy to control 2) From W to MW 3) Normally high velocities 1000 - 10000 rpm 4) Several types (5) Accurate servo control 6) Ideal torque for driving 7) Excellent efficiency 8) Autonomous power system
  59. Servo Motor: The servo motor is most commonly used for high technology devices in the industrial application like automation technology. It is a self contained electrical device, that rotate parts of a machine with high efficiency and great precision. The output shaft of this motor can be moved to a particular angle. Servo motors are mainly used in home electronics, toys, cars, airplanes, etc.
  60. Types of Servo Motors • Servo motors are classified into different types based on their application, such as AC servo • motor, DC servo motor, brushless DC servo motor, positional rotation, continuous rotation and linear servo motor etc. • Typical servo motors comprise of three wires namely, power control and ground. • The shape and size of these motors depend on their applications. • Servo motor is the most common type which is used in hobby applications, robotics due to their simplicity, affordability and reliability of control by microprocessors.
  61. DC Servo Motor • The motor which is used as a DC servo motor generally have a separate DC source in the field of winding & armature winding. • The control can be archived either by controlling the armature current or field current. • Field control includes some particular advantages over armature control. • In the same way armature control includes some advantages over field control. • Based on the applications the control should be applied to • the DC servo motor. • DC servo motor provides very accurate and also fast respond to start or stop command signals due to the low armature inductive reactance. • DC servo motors are used in similar equipment's and • computerized numerically controlled machines.
  62. AC Servo Motor AC servo motor is an AC motor that includes encoder is used with controllers for giving closed loop control and feedback. This motor can be placed to high accuracy and also controlled precisely as compulsory for the applications. Frequently these motors have higher designs of tolerance or better bearings and some simple designs also use higher voltages in order to accomplish greater torque. Applications of an AC motor mainly involve in automation, robotics, CNC machinery, and other applications a high level of precision and needful versatility.
  63. Positional Rotation Servo Motor • Positional rotation servo motor is a most common type of servo motor. • The shaft’s o/p rotates in about 180o. • It includes physical stops located in the gear mechanism to stop turning outside these • limits to guard the rotation sensor. • These common servos involve in radio controlled water, radio controlled cars, aircraft, • robots, toys and many other applications.
  64. Continuous Rotation Servo Motor Continuous rotation servo motor is quite related to the common positional rotation servo motor, but it can go in any direction indefinitely. The control signal, rather than set the static position of the servo, is understood as the speed and direction of rotation. The range of potential commands sources the servo to rotate clockwise or anticlockwise as preferred, at changing speed, depending on the command signal. This type of motor is used in a radar dish if you are riding one on a robot or you can use one as a drive motor on a mobile robot.
  65. Applications of Servo Motor • The servo motor is small and efficient, but serious to use in some applications like precise position control. This motor is controlled by a pulse width modulator signal. • The applications of servo motors mainly involve in computers, robotics, toys, CD/DVD players, etc. These motors are extensively used in those applications where a particular task is to be done frequently in an exact manner. • The servo motor is used in robotics to activate movements, giving the arm to its precise angle. • The Servo motor is used to start, move and stop conveyor belts carrying the product along with many stages. For instance, product labeling, bottling and packaging • The servo motor is built into the camera to correct a lens of the camera to improve out of focus images. • The servo motor is used in robotic vehicle to control the robot wheels, producing plenty torque to move, start and stop the vehicle and control its speed. • The servo motor is used in solar tracking system to correct the angle of the panel so that each solar • panel stays to face the sun • The Servo motor is used in metal forming and cutting machines to provide specific motion control for milling machines • The Servo motor is used in automatic door openers to control the door in public places like supermarkets, hospitals and theatres
  66. Stepper Motor: A stepper motor is an electromechanical device it converts electrical power into mechanical power. Also it is a brushless, synchronous electric motor that can divide a full rotation into an expansive number of steps. The motor’s position can be controlled accurately without any feedback mechanism, as long as the motor is carefully sized to the application. Stepper motors are similar to switched reluctance motors.
  67. The stepper motor uses the theory of operation for magnets to make the motor shaft turn a precise distance when a pulse of electricity is provided. The stator has eight poles, and the rotor has six poles. The rotor will require 24 pulses of electricity to move the 24 steps to make one complete revolution. Another way to say this is that the rotor will move precisely 15° for each pulse of electricity that the motor receives.
  68. Working Principle: Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple toothed electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, for example a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes the gear’s teeth magnetically attracted to the electromagnet’s teeth. The point when the gear’s teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned ON and the first is turned OFF, the gear rotates slightly to align with the next one and from there the process is repeated.
  69. Each of those slight rotations is called a step, with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise. Stepper motor doesn’t rotate continuously, they rotate in steps.  There are 4 coils with 90o angle between each other fixed on the stator. The stepper motor connections are determined by the way the coils are interconnected. In stepper motor, the coils are not connected together. The motor has 90o rotation step with the coils being energized in a cyclic order, determining the shaft rotation direction.  The working of this motor is shown by operating the switch. The coils are activated in series in 1 sec intervals. The shaft rotates 90o each time the next coil is activated. Its low speed torque will vary directly with current.
  70. Types of Stepper Motor: There are three main types of stepper motors, they are: 1.Permanent magnet stepper 2.Variable reluctance stepper 3.Hybrid synchronous stepper Permanent Magnet Stepper Motor: Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets. Variable Reluctance Stepper Motor: Variable reluctance (VR) motors have a plain iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles. Hybrid Synchronous Stepper Motor: Hybrid stepper motors are named because they use a combination of permanent magnet (PM) and variable reluctance (VR) techniques to achieve maximum power in a small package size.
  71. Advantages of Stepper Motor: 1.The rotation angle of the motor is proportional to the input pulse. 2.The motor has full torque at standstill. 3.Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3 – 5% of a step and this error is non cumulative from one step to the next. 4.Excellent response to starting, stopping and reversing. 5.Very reliable since there are no contact brushes in the motor. Therefore the life of the motor is simply dependent on the life of the bearing. 6.The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control. 7.It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft. 8.A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses.
  72. Applications: 1.Industrial Machines – Stepper motors are used in automotive gauges and machine tooling automated production equipment's. 2.Security – new surveillance products for the security industry. 3.Medical – Stepper motors are used inside medical scanners, samplers, and also found inside digital dental photography, fluid pumps, respirators and blood analysis machinery. 4.Consumer Electronics – Stepper motors in cameras for automatic digital camera focus and zoom functions. And also have business machines applications, computer peripherals applications.
  73. Permanent Magnet DC Motor In a DC motor, an armature rotates inside a magnetic field. Basic working principle of DC motor is based on the fact that whenever a current carrying conductor is placed inside a magnetic field, there will be mechanical force experienced by that conductor. Working Principle of Permanent Magnet DC Motor or PMDC Motor The working principle of PMDC motor is just similar to the general working principle of DC motor. That is when a carrying conductor comes inside a magnetic field, a mechanical force will be experienced by the conductor and the direction of this force is governed by Fleming’s left hand rule. As in a permanent magnet DC motor, the armature is placed inside the magnetic field of permanent magnet; the armature rotates in the direction of the generated force.
  74. Here each conductor of the armature experiences the mechanical force F = B.I.L Newton where, B is the magnetic field strength in Tesla (weber / m2), I is the current in Ampere flowing through that conductor and L is length of the conductor in metre comes under the magnetic field. Each conductor of the armature experiences a force and the compilation of those forces produces a torque, which tends to rotate the armature. Equivalent Circuit of Permanent Magnet DC Motor or PMDC Motor As in PMDC motor the field is produced by permanent magnet, there is no need of drawing field coils in the equivalent circuit of permanent magnet DC motor. The supply voltage to the armature will have armature resistance drop and rest of the supply voltage is countered by back emf of the motor. Hence voltage equation of the motor is given by, Where, I is armature current and R is armature resistance of the motor. Eb is the back emf and V is the supply voltage.
  75. Advantages of Permanent Magnet DC Motor or PMDC Motor PMDC motor have some advantages over other types of DC motors. They are : 1.No need of field excitation arrangement. 2.No input power in consumed for excitation which improve efficiency of DC motor. 3.No field coil hence space for field coil is saved which reduces the overall size of the motor. 4.Cheaper and economical for fractional kW rated applications.
  76. Disadvantages of Permanent Magnet DC Motor or PMDC Motor 1.In this case, the armature reaction of DC motor cannot be compensated hence the magnetic strength of the field may get weak due to demagnetizing effect armature reaction. 2.There is also a chance of getting the poles permanently demagnetized (partial) due to excessive armature current during starting, reversal and overloading condition of the motor. 3.Another major disadvantage of PMDC motor is that, the field in the air gap is fixed and limited and it cannot be controlled externally. Therefore, very efficient speed control of DC motor in this type of motor is difficult. Applications of Permanent Magnet DC Motor or PMDC Motor PMDC motor is extensively used where small DC motors are required and also very effective control is not required, such as in automobiles starter, toys, wipers, washers, hot blowers, air conditioners, computer disc drives and in many more.
  77. ThankingY ou