Cathode Ray Tube(CRT)
ELECTRON GUN ASSEMBLY: • It is used for producing a strain of electrons. • The electron gun assembly consists of an indirectly heated cathode, A control grid surrounding the cathode, a Focusing anode and an accelerating anode. • The solo function of it is to provide a focused electron beam which is accelerated towards the phosphorus screen. • The rate of emission of electrons or say intensity depends on magnitude of Cathode current which is controlled by the control grid. DEFLECTION PLATE ASSEMBLY : • The electron beam passes through the two pairs of deflection plates. • One pair of deflection plate is mounted vertically and deflects the beam horizontal and called horizontal deflection plate. • other pair mounted horizontally deflects beam in vertical direction and therefore is called vertical deflection plate. • The electron beam will be deflected to left or right of the tube axis according to the conditions that whether the plates are charged. SCREEN FOR CRT : • The end wall of CRT ,called the screen of CRT is coated with phosphor. • When electron beam strikes the CRT screen, a spot of light is produced on the screen. • The phosphor absorbs the kinetic energy of the bombarding electrons and emits energy at a lower frequency in a visual spectrum. • Among the fluorescent materials used are zinc silicate, calcium tungstate and zinc sulphide. • The intensity of light emitted from screen of CRT is called luminance. GLASS BODY AND BASE : • The whole assembly is protected in a conical highly evacuated glass housing through suitable support’s. • The inner walls of CRT between necks and screen are usually coated with a conducting material known as aquadag and this coating is electrically connected to the accelerating anode. • The coating is provided in order to accelerate the electron beam after passing between the deflection plate. WORKING OF CATHODE RAY TUBE
• Heater element is energized by alternating current to obtain high emission of electron from cathode. • Control grid is biased negative with respect to cathode it controls the density of electron beam to focus the electron beam on the screen focusing anode is used, the focusing anode operate at a potential of twelve hundred (1200 V) and accelerating anode at 2000 V to accelerate the electron beam • the focusing anode operate at a potential of twelve hundred (1200 V) and accelerating anode at 2000 V to accelerate the electron beam • The screen consists of a glass which is coated by some florescent material lie zinc silicate. Which is semitransparant phosphor substance. • When high velocity electron beam structs the phosphorescent screen the light emits from it. The property of phosphor to emit light when its atoms are excited is called fluorescence. Advantages
• CRT’s are less e pensive than other displa technologies. • They operate at any resolution, geometry and aspect ratio without decreasing the image quality. • CRTs produce the very best color and gray-scale for all professional calibrations. • Excellent viewing angle. • It maintains good brightness and gives long life service.
Application CRO Objectives: This final chapter discusses the key instruments of electronic measurement with special emphasis on the most versatile instrument of electronic measurement—the cathode-ray oscilloscope (CRO). The objective of this book will remain unrealized without a discussion on the CRO. The chapter begins with the details of construction of the CRO, and proceeds to examine the active and passive mode input–output waveforms for filter circuits and lead-lag network delay. This will be followed by a detailed study of the dual beam CRO and its uses in op-amp circuit integrator, differentiator, inverting and non-inverting circuits, comparative waveform study, and accurate measurement with impeccable visual display. In addition to the CRO, the chapter also examines the sweep frequency generator, the function generator, the sine wave generator, the square wave generator and the AF signal generator. INTRODUCTION: The cathode-ray oscilloscope (CRO) is a multipurpose display instrument used for the observation, measurement , and analysis of waveforms by plotting amplitude along y-axis and time along x-axis. CRO is generally an x-y plotter; on a single screen it can display different signals applied to different channels. It can measure amplitude, frequencies and phase shift of various signals. Many physical quantities like temperature, pressure and strain can be converted into electrical signals by the use of transducers, and the signals can be displayed on the CRO. A moving luminous spot over the screen displays the signal. CROs are used to study waveforms, and other time-varying phenomena from very low to very high frequencies. The central unit of the oscilloscope is the cathode- ray tube (CRT), and the remaining part of the CRO consists of the circuitry required to operate the cathode-ray tube. Block diagram of a cathode-ray oscilloscope: COMPONENTS OF THE CATHODE-RAY OSCILLOSCOPE:
The CRO consists of the following: (i) CRT (ii) Vertical amplifier (iii) Delay line (iv) Horizontal amplifier (v) Time-base generator (vi) Triggering circuit (vii) Power supply CATHODE-RAY TUBE:
The electron gun or electron emitter, the deflecting system and the fluorescent screen are the three major components of a general purpose CRT. A detailed diagram of the cathode-ray oscilloscope is given in Fig. 14-2. Electron Gun:
In the electron gun of the CRT, electrons are emitted, converted into a sharp beam and focused upon the fluorescent screen. The electron beam consists of an indirectly heated cathode, a control grid, an accelerating electrode and a focusing anode. The electrodes are connected to the base pins. The cathode emitting the electrons is surrounded by a control grid with a fine hole at its centre. The accelerated electron beam passes through the fine hole. The negative voltage at the control grid controls the flow of electrons in the electron beam, and consequently, the brightness of the spot on the CRO screen is controlled. Deflection Systems:
Electrostatic deflection of an electron beam is used in a general purpose oscilloscope. The deflecting system consists of a pair of horizontal and vertical deflecting plates. Let us consider two parallel vertical deflecting plates P1 and P2. The beam is focused at point O on the screen in the absence of a deflecting plate voltage.
If a positive voltage is applied to plate P1 with respect to plate P2, the negatively charged electrons are attracted towards the positive plate P1, and these electrons will come to focus at pointY1 on the fluorescent screen.
Deflection Systems:
The deflection is proportional to the deflecting voltage between the plates. If the polarity of the deflecting voltage is reversed, the spot appears at the point Y2, as shown in Fig. 14-3(a). Deflection Systems:
To deflect the beam horizontally, an alternating voltage is applied to the horizontal deflecting plates and the spot on the screen horizontally, as shown in Fig. 14-3(b). The electrons will focus at point X2. By changing the polarity of voltage, the beam will focus at point X1. Thus, the horizontal movement is controlled along X1OX2 line. Spot Beam Deflection Sensitivity: Electrostatic Deflection: Electrostatic Deflection: Electrostatic Deflection: Electrostatic Deflection: Fluorescent Screen:
Phosphor is used as screen material on the inner surface of a CRT. Phosphor absorbs the energy of the incident electrons. The spot of light is produced on the screen where the electron beam hits. The bombarding electrons striking the screen, release secondary emission electrons. These electrons are collected or trapped by an aqueous solution of graphite called “Aquadag” which is connected to the second anode. Collection of the secondary electrons is necessary to keep the screen in a state of electrical equilibrium. The type of phosphor used, determines the color of the light spot. The brightest available phosphor isotope, P31, produces yellow–green light with relative luminance of 99.99%. Display waveform on the screen:
Figure 14-5(a) shows a sine wave applied to vertical deflecting plates and a repetitive ramp or saw-tooth applied to the horizontal plates. The ramp waveform at the horizontal plates causes the electron beam to be deflected horizontally across the screen. If the waveforms are perfectly synchronized then the exact sine wave applied to the vertical display appears on the CRO display screen. Triangular waveform:
Similarly the display of the triangular waveform is as shown in Fig. 14-5(b). TIME-BASE GENERATORS:
The CRO is used to display a waveform that varies as a function of time. If the wave form is to be accurately reproduced, the beam should have a constant horizontal velocity. As the beam velocity is a function of the deflecting voltage, the deflecting voltage must increase linearly with time. A voltage with such characteristics is called a ramp voltage. If the voltage decreases rapidly to zero—with the waveform repeatedly produced, as shown in Fig. 14-6—we observe a pattern which is generally called a saw-tooth waveform. The time taken to return to its initial value is known as flyback or return time. Simple saw-tooth generator & associated waveforms:
The circuit shown in Fig. 14-7(a) is a simple sweep circuit, in which the capacitor C charges through the resistor R. The capacitor discharges periodically through the transistor T1, which causes the waveform shown in Fig. 14-7(b) to appear across the capacitor. The signal voltage, Vi which must be applied to the base of the transistor to turn it ON for short time intervals is also shown in Fig. 14-7(b). Time-base generator using UJT:
The continuous sweep CRO uses the UJT as a time-base generator. When power is first applied to the UJT, it is in the OFF state and CT changes exponentially through RT . The UJT emitter voltage VE rises towards VBB and VE reaches the plate voltage VP. The emitter-to-base diode becomes forward biased and the UJT triggers ON. This provides a low resistance discharge path and the capacitor discharges rapidly. When the emitter voltage VE reaches the minimum value rapidly, the UJT goes OFF. The capacitor recharges and the cycles repeat.
To improve the sweep linearity, two separate voltage supplies are used; a low voltage supply for the UJT and a high voltage supply for the RTCT circuit. This circuit is as shown in Fig. 14-7(c).
RT is used for continuous control of frequency within a range and CT is varied or changed in steps. They are sometimes known as timing resistor and timing capacitor. Oscilloscope Amplifiers:
The purpose of an oscilloscope is to produce a faithful representation of the signals applied to its input terminals. Considerable attention has to be paid to the design of these amplifiers for this purpose. The oscillographic amplifiers can be classified into two major categories. (i) AC-coupled amplifiers (ii) DC-coupled amplifiers The low-cost oscilloscopes generally use ac-coupled amplifiers. The ac amplifiers, used in oscilloscopes, are required for laboratory purposes. The dc-coupled amplifiers are quite expensive. They offer the advantage of responding to dc voltages, so it is possible to measure dc voltages as pure signals and ac signals superimposed upon the dc signals. DC-coupled amplifiers have another advantage. They eliminate the problems of low-frequency phase shift and waveform distortion while observing low-frequency pulse train. The amplifiers can be classified according to bandwidth use also: (i) Narrow-bandwidth amplifiers (ii) Broad-bandwidth amplifiers Vertical Amplifiers:
Vertical amplifiers determines the sensitivity and bandwidth of an oscilloscope. Sensitivity, which is expressed in terms of V/cm of vertical deflection at the mid-band frequency. The gain of the vertical amplifier determines the smallest signal that the oscilloscope can satisfactorily measure by reproducing it on the CRT screen. The sensitivity of an oscilloscope is directly proportional to the gain of the vertical amplifier. So, as the gain increases the sensitivity also increases. The vertical sensitivity measures how much the electron beam will be deflected for a specified input signal. The CRT screen is covered with a plastic grid pattern called a graticule. The spacing between the grids lines is typically 10 mm. Vertical sensitivity is generally expressed in volts per division. The vertical sensitivity of an oscilloscope measures the smallest deflection factor that can be selected with the rotary switch. Frequency response: The bandwidth of an oscilloscope detects the range of frequencies that can be accurately reproduced on the CRT screen. The greater the bandwidth, the wider is the range of observed frequencies. The bandwidth of an oscilloscope is the range of frequencies over which the gain of the vertical amplifier stays within 3 db of the mid-band frequency gain, as shown in Fig. 14-8. Rise time is defined as the time required for the edge to rise from 10–90% of its maximum amplitude. An approximate relation is given as follows: MEASUREMENTS USING THE CATHODE-RAY OSCILLOSCOPE:
1) Measurement of Frequency: MEASUREMENTS USING THE CATHODE-RAY OSCILLOSCOPE: 2) Measurement of Phase:
3 Measurement of Phase Using Lissajous Figures: Measurement of Phase Using Lissajous Figures: Measurement of Phase Using Lissajous Figures: Measurement of Phase Using Lissajous Figures: Measurement of Phase Using Lissajous Figures: TYPES OF THE CATHODE-RAY OSCILLOSCOPES:
The categorization of CROs is done on the basis of whether they are digital or analog. Digital CROs can be further classified as storage oscilloscopes. 1. Analog CRO: In an analog CRO, the amplitude, phase and frequency are measured from the displayed waveform, through direct manual reading. 2. Digital CRO: A digital CRO offers digital read-out of signal information, i.e., the time, voltage or frequency along with signal display. It consists of an electronic counter along with the main body of the CRO. 3. Storage CRO: A storage CRO retains the display up to a substantial amount of time after the first trace has appeared on the screen. The storage CRO is also useful for the display of waveforms of low-frequency signals. 4. Dual-Beam CRO: In the dual-beam CRO two electron beams fall on a single CRT. The dual-gun CRT generates two different beams. These two beams produce two spots of light on the CRT screen which make the simultaneous observation of two different signal waveforms possible. The comparison of input and its corresponding output becomes easier using the dual-beam CRO. SWEEP FREQUENCY GENERATOR:
A sweep frequency generator is a signal generator which can automatically vary its frequency smoothly and continuously over an entire frequency range. Figure 14-15 shows the basic block diagram of a sweep frequency generator. The sweep frequency generator has the ramp generator and the voltage-tuned oscillator as its basic components. Applications of the Sweep Frequency Generator: FUNCTION GENERATOR:
The basic components of a function generator are: (i) Integrator (ii) Schmitt trigger circuit (iii) Sine wave converter (iv) Attenuator SINE WAVE GENERATOR:
A sine wave is produced by converting a triangular wave, applying proper circuits. The triangular wave is produced by employing an integrator and a Schmitt trigger circuit. This triangular wave is then converted to a sine wave using the diode loading circuit ,as shown in Fig. 14-19. Resistors R1 and R2 behave as the voltage divider. When VR2 exceeds V1, the diode D1 becomes forward- biased. There is more attenuation of the output voltage levels above V1 than levels below V1. With the presence of the diode D1 and resistor R3 in the circuit, the output voltage rises less steeply. The output voltage falls below V1 and the diode stops conducting, as it is in reverse-bias. The circuit behaves as a simple voltage-divider circuit. This is also true for the negative half-cycle of the input Vi . If R3 is carefully chosen to be the same as R4 , the negative and the positive cycles of the output voltage will be the same. The output is an approximate sine wave. SINE WAVE GENERATOR:
The approximation may be further improved by employing a six-level diode loading circuit, as shown in Fig. 14-20(a). SINE WAVE GENERATOR:
The circuit is adjusted by comparing a 1 kHz sine wave and the output of the triangular/sine wave converter on a dual-track CRO. R1, R2, R3 and the peak amplitude of Ei are adjusted in sequence for the best sinusoidal shape. CIRCUIT DIAGRAM OF SINE WAVE GENERATOR: SQUARE WAVE GENERATOR A square wave can be most easily obtained from an operational amplifier astable multi-vibrator. An astable multi-vibrator has no stable state—the output oscillates continuously between high and low states. In Fig. 14-21, the block comprising the op-amp, resistors R2 and R3 constitutes a Schmitt trigger circuit. The capacitor C1 gets charged through the resistor R1. When the voltage of the capacitor reaches the upper trigger point of the Schmitt trigger circuit, the output of the op-amp switches to output low. This is because the Schmitt trigger is a non-inverting type. Now, when the op-amp output is low, the capacitor C1 starts getting discharged. SQUARE WAVE GENERATOR:
As the capacitor discharges and the capacitor voltage reaches the lower trigger point of the Schmitt trigger, the output of the op-amp switches back to the output high state. The capacitor charges through the resistor again and the next cycle begins. The process is repetitive and produces a square wave at the output. The frequency of the output square wave depends on the time taken by the capacitor to get charged and discharged when the capacitor voltage varies from UTP (upper trigger point) and LTP (lower trigger point). AF SIGNAL GENERATOR: POINTS TO REMEMBER:
1. CRO is used to study waveforms. 2. CRT is the main component of a CRO. 3. Prosperous P31 is used for the fluorescent screen of a CRO. 4. A CRO has the following components: (a) Electron gun (b) Deflecting system (c) Florescent screen 5. Lissajous figures are used to measure frequency and phase of the waves under study. 6. A time-base generator produces saw-tooth voltage. 7. An oscilloscope amplifier is used to provide a faithful representation of input signal applied to its input terminals. IMPORTANT FORMULAE: DATA LOGGERS • A data logger (also data logger or data recorder) is an electronic device that records data over time or in relation to location either with a built in instruments or sensors or via external instruments and sensors. Increasingly, but not entirely, they are based on a digital processor (or computer). • They generally are small, battery powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors. • Some data loggers interface with a personal computer and utilize software to activate the data logger and view and analyze the collected data, while others have a local interface device (keypad, LCD) and can be used as a stand-alone device. Data loggers vary between general purpose types for a range of measurement applications to very specific devices for measuring in one environment or application type only. • It is common for general purpose types to be programmable; however, many remain as static machines with only a limited number or no changeable parameters. Electronic data loggers have replaced chart recorders in many applications. One of the primary benefits of using data loggers is the ability to automatically collect data on a 24-hour basis. Upon activation, data loggers are typically deployed and left unattended to measure and record information for the duration of the monitoring period. This allows for a comprehensive, accurate picture of the environmental conditions being monitored, such as air temperature and relative humidity.
• Sensors are used to take readings or measurements at regular intervals of their environment. • The sensors could be collecting data on a wide range of things such as temperature, humidity, pressure, wind speed, water currents, electrical voltage, pH readings etc. • The sensors may be either analogue or digital. If they take analogue readings, an Analogue to Digital Converter (ADC) will be needed to convert the signal into digital data which the computer can understand. • As the sensor takes a reading, the data is sent though a cable or wireless link to the data logger. • The data logger usually stores the data for a period of time before sending it in a large batch to a computer which will process and analyse it. • A data logger is often a hand-held battery-operated device which has a large amount of memory.
• Data in this format can be exported to a spread sheet application such as Microsoft Excel, for further manipulation. Once the data is in the pc, it can be saved as a file on the computer or floppy disk for recall at a later date or printed. Madge Tech data loggers are small, battery powered ,intelligent electronic devices that record measurements of physical parameters in the world for later retrieval by a computer. As the technology improves, significant achievements in performance can be made. DIGITAL PLOTTERS
1 Plotter
• A plotter is a printer that uses a pen that moves over a large revolving sheet of paper. • It is used in engineering, drafting, map making, and seismology. 2 • Computer plotters are used for drawing point-to-point lines and vector graphics. A plotter-printer uses inkjet heads to draw lines based on commands from a computer.
3
• Plotters are typically used in engineering to draw blueprints using CAD (computer aided design) and CAM (computer aided manufacturing). These printers were the first type of printer that could print color graphics. Plotter technology has advanced, and the once high-tech pen plotters have fallen into obscurity. • Another form of plotter is a cutting plotter, which uses knives to cut material used in graphics for advertising materials like the magnetic signs used on vehicles. As of 2014, laser cutters are starting to replace cutting plotters due to a higher level of
versatility. 4
• A drum plotter is a type of printer typically used to produce graphics such as architectural blueprints created with CAD applications. The drum plotter uses a drum to move the paper left and right while one or more pens draw up and down, according to the Chron website. Using more than one pen allows the plotter to draw in different colors.
5 • Another type of plotter is the flatbed plotter. This plotter uses a system where the paper is fixed, and one or more pens move up and down as well as left and right to produce the graphic. By using a drum to move the paper, drum plotters have a smaller footprint than the finished size of the paper.
6 • Plotter • A plotter is a special output device used to produce hardcopies of graphs and designs on the paper. A plotter is typically used to print large-format graphs or maps such as construction maps, engineering drawings and big posters. Plotters are divided into two types: • 1. Drum plotters • 2. Flatbed plotters
7 • Drum Plotter • A drum plotter is also known as Roller Plotter. It consists of a drum or roller on which a paper is placed and the drum rotates back and forth to produce the graph on the paper. It also consists of mechanical device known as Robotic Drawing Arm that holds a set of colored ink pens or pencils. The Robotic Drawing Arm moves side to side as the paper are rolled back and forth through the roller. In this way, a perfect graph or map is created on the paper. This work is done under the control of computer. Drum Plotters are used to produce continuous output, such as plotting earthquake activity. •
8 9 • Flatbed Plotter • A flatbed plotter is also known as Table Plotter. It plots on paper that is spread and fixed over a rectangular flatbed table. The flatbed plotter uses two robotic drawing arms, each of which holds a set of colored ink pens or pencils. The drawing arms move over the stationary paper and draw the graph on the paper. Typically, the plot size is equal to the area of a bed. The plot size may be 20- by-50 feet. It is used in the design of cars, ships, aircrafts, buildings, highways etc. Flatbed plotter is very slow in drawing or printing graphs. The large and complicated drawing can take several hours to print. The main reason of the slow printing is due to the movement mechanical devices.Today, mechanical plotters have been replaced by thermal, electrostatic and ink jet plotters. These systems are faster and cheaper. 10 They also produce large size drawings. • 11 • A dot-matrix display is a display device used to display information on machines, clocks, railway departure indicators and many other devices requiring a simple display device of limited resolution. • The display consists of a dot matrix of lights or mechanical indicators arranged in a rectangular configuration (other shapes are also possible, although not common) such that by switching on or off selected lights, text or graphics can be displayed. A dot matrix controller converts instructions from a processor into signals which
turns on or off lights in the matrix so that the 12 required display is produced. • Common sizes of dot matrix displays: • 128×16 (Two lined) • 128×32 (Four lined) • 128×64 (Eight lined) • Other sizes include: • 92×31 (Four or three lined
13 • A common size for a character is 5×7 pixels, either separated with blank lines with no dots (in most text-only displays), or with lines of blank pixels (making the real size 6x8). This is seen on most graphic calculators, such as Casio calculators or TI-82 and superior. • A smaller size is 3×5 (or 4x6 when separated with blank pixels). This is seen on the TI-80 calculator as a "pure", fixed-size 3×5 font, or on most 7×5 calculators as a proportional (1×5 to 5×5) font. The disadvantage of the 7×5 matrix and smaller is that lower case characters with descenders are not practical. A matrix of 11×9 is often used to give far superior resolution. • Dot matrix displays of sufficient resolution can be programmed to emulate the customary seven-
segment numeral patterns. 14 • A larger size is 5×9 pixels, which is used on many Light Emitting Diode: LED What is an LED?
Light-emitting diode Semiconductor Has polarity
LED Cross sectional view LED: How It Works When current flows across a diode
Negative electrons move one way and positive holes move the other way LED: How It Works The wholes exist at a lower energy level than the free electrons
Therefore when a free electrons falls it losses energy LED: How It Works This energy is emitted in a form of a photon, which causes light
The color of the light is determined by the fall of the electron and hence energy level of the photon Inside a Light Emitting Diode
1. Transparent Plastic Case 2. Terminal Pins 3. Diode
The emitting light may be visible or invisible The amount of light output is directly propositional to the forward current It’s a semiconductor material used to fabricate LED are Ga As-gallium arsenide Ga Asp- gallium arsenide phosphide Ga P- gallium phosphide Metal film anode connection in Top of the device Gold film applied in bottom of the device Ga As-gallium arsenide-Invisible light emitting Ga Asp- gallium arsenide phosphide-Red or yellow Ga P- gallium phosphide-white red or green operation Recombination takes place,after that electrons lying in the conduction band and holes lying in the valance band Energy difference between the band is radiated in the form light In semiconductor device energy emitted in the form of heat. LED have certain voltage drop when connected to the circuits ,its depends on the LED current (10mA to 50mA) Kinds of LEDs Advantages and Disadvantages 1.Low power consumption 2.Very fast action 3.Operting voltage and current is less 4.No effect due to mechanical vibration
1.Low efficiency 2.Radiated output power is temperature dependent 3.Very sensitive device Applications
1.Displays of numeric and alphanumeric characters 2.In optical switching conditions 3.Decorating instruments How to Connect a LED:
Requires 1.5~2.5V and 10 mA To prevent overloading, use resistor 470 Ω
How to Connect a LED: Connect LED to BS2
LED is on when P0 is high
LED is on when P1 is low
Connect Multiple LEDs to BS2
8 LEDs are connected to BS2 each I/O pin (P0-P7) is allowed to sink 6.25mA
Case Study: Blinking LED Case Study: Blinking LED Pbasic program to make an LED blink
output 0 Make pin0 an output
Main: Loop begins here low 0 Turn LED on pause 1000 Pause for 1 sec high 0 Turn LED off pause 1000 Pause for 1 sec goto Main Go back to beginning of loop Experiments
Flash an LED 1. Single LED 2. Multiple LEDs Traffic Light by use of LEDs LCD
A liquid crystal display or LCD draws its definition from its name itself. It is combination of two states of matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image. Liquid crystal displays are laptop super-thin technology display screen . That are generally used in computer screen, TVs, cell phones and portable video games. LCD’s technologies allow displays to be much thinner when compared to cathode ray tube (CRT) technology.
Types of LCD
1.Dynamic Scattering 2.Field effect type
Advantages of an LCD’s: LCD’s consumes less amount of power compared to CRT and LED LCD’s are consist of some microwatts for display in comparison to some mill watts for LED’s LCDs are of low cost Provides excellent contrast LCD’s are thinner and lighter when compared to cathode ray tube and LED Disadvantages of an LCD’s: Require additional light sources Range of temperature is limited for operation Low reliability Speed is very low LCD’s need an AC drive
Applications Liquid crystal technology has major applications in the field of science and engineering as well on electronic devices. Liquid crystal thermometer Optical imaging The liquid crystal display technique is also applicable in visualization of the radio frequency waves in the waveguide Used in the medical applications Types of Storage Devices Categorizing Storage Devices
• Storage devices hold data, even when the computer is turned off.
• The physical material that actually holds data is called a storage medium. The surface of a floppy disk is a storage medium.
• The hardware that writes data to or reads data from a storage medium is called a storage device. A floppy disk drive is a storage device.
• The two primary storage technologies are magnetic and optical. The primary types of magnetic storage are:
Diskettes (floppy disks) •
• Hard disks
• High-capacity floppy disks
• Disk cartridges
• Magnetic tape
The primary types of optical storage are:
• Compact Disk Read-Only Memory (CD-ROM)
• Digital Video Disk Read-Only Memory (DVD-ROM)
• CD-Recordable (CD-R)
• CD-Rewritable (CD-RW)
• PhotoCD Magnetic Storage Devices
• How Magnetic Storage Works
• Formatting
• Disk Areas
• Diskettes
• Hard Disks
• Disk Capacities
• Other Magnetic Storage Devices
Magnetic Storage Devices - How Magnetic Storage Works
• A magnetic disk's medium contains iron particles, which can be polarized—given a magnetic charge—in one of two directions.
• Each particle's direction represents a 1 (on) or 0 (off), representing each bit of data that the CPU can recognize.
• A disk drive uses read/write heads containing electromagnets to create magnetic charges on the medium.
Write head
Medium
Random particles Current flow (no data stored) (write operation)
Organized particles (represent data) As the medium rotates, the head writes the data. Magnetic Storage Devices - Formatting
• Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.
• During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.
• The OS organizes sectors into groups, called clusters, then tracks each file's location according to the clusters it occupies. Formatted Disk Magnetic Storage Devices - Disk Areas
When a disk is formatted, the OS creates four areas on its surface: • Boot sector – stores the master boot record, a small program that runs when you first start (boot) the computer
• File allocation table (FAT) – a log that records each file's location and each sector's status
• Root folder – enables the user to store data on the disk in a logical way
• Data area – the portion of the disk that actually holds data
Magnetic Storage Devices - Diskettes
• Diskette drives, also known as floppy disk drives, read and write to diskettes (called floppy disks or floppies).
• Diskettes are used to transfer files between computers, as a means for distributing software, and as a backup medium.
• Diskettes come in two sizes: 5.25-inch and 3.5-inch. 3.5 inch floppy and drive Magnetic Storage Devices - Hard Disks
• Hard disks use multiple platters, stacked on a spindle. Each platter has two read/write heads, one for each side.
• Hard disks use higher-quality media and a faster rotational speed than diskettes.
• Removable hard disks combine high capacity with the convenience of diskettes. Read/write heads Magnetic Storage Devices - Disk Capacities
• Diskettes are available in different capacities, but the most common store 1.44 MB.
• Hard disks store large amounts of data. New PCs feature hard disks with capacities of 10 GB and higher. Magnetic Storage Devices - Other Magnetic Storage Devices
• High-capacity floppy disks offer capacities up to 250 MB and the portability of standard floppy disks.
• Disk cartridges are like small removable hard disks, and can store up to 2 GB.
• Magnetic tape systems offer very slow data access, but provide large capacities and low cost.
Due to long access times, tape drives are used mainly for backups. Optical Storage Devices
• How Optical Storage Works
• CD-ROM
CD-ROM Speeds and Uses •
• DVD-ROM
• Other Optical Storage Devices
Optical Storage Devices – How Optical Storage Works
• An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data.
• To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently.
• When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (off). A land reflects light back to its source, representing a bit value of 1 (on). 1 0 Optical Storage Devices – CD-ROM
• In PCs, the most commonly used optical storage technology is called Compact Disk Read-Only Memory (CD-ROM).
• A standard CD-ROM disk can store up to 650 MB of data, or about 70 minutes of audio.
• Once data is written to a standard CD-ROM disk, the data cannot be altered or overwritten. Optical Storage Devices – CD-ROM Speeds and Uses
• Early CD-ROM drives were called single speed, and read data at a rate of 150 KBps. (Hard disks transfer data at rates of 5 – 15 MBps).
• CD-ROM drives now can transfer data at speeds of up to 7800 KBps. Data transfer speeds are getting
faster.
• CD-ROM is typically used to store software programs. CDs can store audio and video data, as well as text and program instructions. Optical Storage Devices - DVD-ROM
• A variation of CD-ROM is called Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.
• Standard DVD disks store up to 9.4 GB of data— enough to store an entire movie. Dual-layer DVD disks can store up to 17 GB.
• DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.
Optical Storage Devices - Other Optical Storage Devices
• A CD-Recordable (CD-R) drive lets you record your own CDs, but data cannot be overwritten once it is recorded to the disk.
• A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.
• PhotoCD technology is used to store digital photographs. Printer its types, working and usefulness
1 Printers
Impact Printers Non-Impact Printers
Daisy Dot- Inkjet Thermal Laser wheel Matrix
2 What is a printer?
An external hardware device responsible for taking computer data and generating a hard copy of that data. Printers are one of the most commonly used peripherals and they print text and still images on the paper.
3 “Print Quality”
(1) Near typeset quality: A Lower quality print similar to the output of a type- writer. (2) Letter quality: Print made up by fully formed (solid line) characters. (3) Near letter quality: A print of high quality formed by multiple passes of print head over the same letter. (4) Standard quality: A high quality print formed by a single pass of the print head. (5) Draft quality: A print formed with minimum number of dots or lines and are smaller than the standard quality characters.
4 “Factors affecting print quality”
(1) DPI: It is a measurement of printer’s resolution indicating how many ink dots can be placed by the printer in one square inch. The higher the DPI, the sharper is image. (2) Type of printer: Each type of printer has its own capabilities of printing. Some types of printers produce high quality print while other produce low quality print. (3) Print Mode: The printing mode may also affect the quality. For example the draft mode increases the print rate but quality is reduced. (4) Toner: The quality and amount of toner also affects print quality.
5 “Impact Printer” These printers have a mechanism that touches the paper to create an image. These printers work by banging a print head containing a number of metal pins An impact printer showing details which strike an inked of print head.sss ribbon placed between the print head and the paper. 6 “Non-Impact Printers”
These printers create an image on the print medium without the use of force. They don’t touch the paper while creating an image. Non-impact printers are much quieter than impact printers as they A non-impact printer don’t strike the paper.
The term dot matrix refers to the process of placing dots to form an image. Its speed is usually 30 to 550 characters per second (cps). This is the cheapest and the most noisy printer and has a low print quality. Dot Matrix were 1st introduced by Centronics in 1970. 8 How Dot-Matrix works?
The dot matrix forms images one character at a time as the print head moves across the paper. Uses tiny pins to hit an ink ribbon and the paper much as a typewriter does. This printer arranges dots to form characters and all kinds of images. 9 to 24 vertical column pins are contained in a rectangular print head. When print head moves across the paper, pins are activated to form a dotted character image. These printers can produce carbon copies along with the originals. 9 “A typical dot matrix output”
10 “Advantages/Dis-advatages of Dot-Matrix”
Advantages: (1) In-expensive. (2) Low per page cost. (3) Energy efficient. Dis-advantages: (1) Noisy (2) Low resolution (3) Limited fonts flexibility (4) Poor quality graphics output.
11 “Daisy Wheel Printer”
A daisy wheel printer is basically an impact printer consisting of a wheel and attached extensions on which molded metal characters are mounted. A daisy wheel printer produces letter quality print and it can’t produce graphics output. 12 How Daisy wheel printer works?
In a daisy wheel printer, a hammer presses the wheel against a ribbon which in turn makes an ink stain on the paper in the form of a character mounted on the wheel extensions.
These printers are very noisy as there occur great movement during the printing. Its printing speed is also very slow ,i.e. less than 90cps. 13 “Ink-Jet Printer” It is a non-impact printer producing a high quality print. A standard Inkjet printer has a resolution of 300dpi. Newer models have further improved dpi. Inkjet printers were introduced in the later half of 1980s and are very popular owing to their extra-ordinary performance.
14 How Inkjet Printer works? (1) Print head having four ink cartridges moves . (2) Software instructs where to apply dots of ink, which color and what quantity to use. (3) Electrical pulses are sent to the resistors behind each nozzle. (4) Vapor bubbles of ink are formed by resistors and the ink is forced to the paper through nozzles. Color cartridge showing inkjet nozzles. (5) A matrix of dots forms characters and pictures.
15 Inside an Inkjet Printer? (1) Print head Assembly: Contains a series of nozzles (2) Ink Cartridge: Depending on the model & manufacturing of printers, ink cartridge come in various combinations. (3) Print head stepper motor: A stepper motor moves the print head assembly back and forth across the paper. 16 Inside an Inkjet printer?
(4) Stabilizer bar: The movement of print head is controlled and made precise by a stabilizer bar. (5) Belt:
A belt is used to attach print head assembly to Here you can see stabilizer bar and belt the stepper motor.
17 Inside the Inkjet Printer?
(6) Paper tray/feeder:
It enables the user to load the paper into the printer.
(7) Rollers:
Control the movement of the paper.
(8) Control circuitry:
control all the mechanical aspects of the operation as well as decode the information sent to the printer from the computer.
18 Advantages/ Dis-advantages Advantages:
(1) High resolution output.
(2) Energy efficient.
(3) Many options to select.
Dis-advantages:
(1) Expensive.
(2) Special paper required for higher resolution output.
(3) Time consuming in case of graphics printing. 19 Thermal Printer
Thermal printers are in- expensive printers mostly used in fax machines. The Thermal printers are further classified into two types. (1) Electro thermal printers: A fax machine using a thermal printer (2) Thermal Wax printers:
20 How thermal printer works?
Thermal printers use heated pins and ribbons with different color bands. These printers contain a stick of wax like ink. The ribbon passes in front of a print head that has a series of tiny heated pins. The pins cause the wax to melt and adhere to the paper and when temperature reaches to a certain level, it is hardened.
21 “Laser Printer”
Laser printers use very advanced technology and produce a high quality output. Laser printers can also produce high quality graphics images. Resolution is 600 to 1200dpi.
22 How Laser printer Works?
(1) Paper is fed and the drum rotates. (2) A laser beam conveys information from the computer to a rotating mirror and thus an image is created on the drum. (3)The charges on the drum are ionized and the toner sticks to the drum. (4)Toner is transferred from drum to paper. (5)Heat is applied to fuse the toner on the paper.
23 “Multi-function printer”
A multi function printer abbreviated as MFP is an all purpose device that prints, faxes, copies and scans. A single multi function printer can replace several bulky devices. A multi function printer is also known as AIO. These printers use inkjet technology and provide high quality print but at slow speed.
24 “Plotter” A large scale printer which is very accurate in producing engineering drawings and architectural blueprints. Two types of plotters are flatbed and drum. Flatbed plotters are horizontally aligned while drum plotters are vertically positioned.
25 “Printers for different users”
To choose a printer from a printer’s family following considerations are to be made. (1) What’s the budget? (2) Is color needed or just black& white? (3) What is the Volume of the output? (4) How important is the quality of the output? (5) What special features are needed? (6) Is the printer is to be used by a single user or a whole network?
26
“Printer for Home users”
For home users, the quality of the print and the price of the printer both matter. So a better choice in such case is a portable color Inkjet printer.
If the budget of the user is good enough then the best choice is a personal laser printer which enhances both the speed and quality of the print.
27 “Small and medium offices”
For small and medium scale offices a better option is a multi-function printer which is an integrated device fulfilling various requirement of the office.
For better output, a laser printer is the best choice.
28 “Printers for banks, large business organizations and companies” In banks, large size business environments and companies printers with networking capabilities should be preferred which can increase productivity and reduce the cost without compromising on the quality. Of course laser printer is quite suitable choice but multi-functional printer and inkjet printer can also play vital role.
29 RECORDERS
• Recorder records an electrical or nonelectrical quantities as a function of time . Classified into • Analog recorders A) Graphic recorders( Strip Chart Recorders ,X-Y recorders) B) Oscilloscopic Recorders C) Magnetic tape recorders • Digital recorders • A) Incremental • B)Synchronous Strip Chart Recorders (X-t Recorder)
• Records one or more variables with respect to time. • Consists of • A long roll of graph paper moving vertically • A system for driving the paper at a uniform speed • A stylus for making marks on the moving graph paper ( moves horizontally in proportional to the quantity being recorded) • A Stylus driving system. • Event marker to mark edges of chart • Different types are a)Galvanometer Type – Deflection principle b)Null Type – Comparison Basis/ self balancing Type
Strip Chart Recorders (X-t Recorder)
Galvanometer Type • Use D Arsonval galvanometer • As the current flows through the coil, it deflects. • The deflection is produced by a galvanometer which produces a torque on the account of current passing through the large moving coil situated in a strong magnetic field. • Greater the amplitude of the incoming signal (proportional to the quantity being measured), the grater is the deflection. • Instrument should be critically damped to avoid overshoot. • Does not suitable for fast variations in current ,voltage or power. Only records the average value. Galvanometer Type
Null Type • Change in input produced by the signal upset the balance of the measuring circuit of the recorder. As a result of this unbalance, an error signal is produced that operates on some devices which restore the balance or bring the system to null conditions. • Eg: Potentiometric Recorders , Bridge Recorders, LVDT Recorders. Strip chart Recorder • Advantages: Conversion of data is easier when rectangular coordinated are used. • The rate of movement of the chart can easily be changed to spread out the trace of the variable being observed • Disadvantages: Observing the behavior several hours or days back is not as easy.
13 March 2018 7 X-Y Recorder • Records one or more parameters with respect to some other • Or • x-y recorder is an instrument which gives a graphic record of the relationship between two variables.
• In some type recorders ,Pen moves in two axes
• In X-Y recorders, an emf is plotted as a function
13of March another 2018 emf. 8
X-Y Recorder
13 March 2018 9 Basic X-Y Recorder
13 March 2018 10 X-Y Recorder • This is done by having one self-balancing potentiometer control the position of the rolls. • While another self-balancing potentiometer controls the position of the recording pen.
• In some X-Y recorders, one self-balancing potentiometer circuit moves a recording pen in the X direction
• While another self-balancing potentiometer circuit moves the recording pen in the Y direction, while the paper remains stationary.
13 March 2018 11 X-Y Recorder
• Attenuators are used to bring the input signals to the levels acceptable by the recorder.
• XY recorder is Expensive than strip chart recorder
13 March 2018 12 X-Y Recorder
13 March 2018 13 X-Y Recorder • A signal enters each of the two channels.
• The signals are attenuated to the inherent full scale range of the recorder, the signal then passes to a balance circuit where it is compared with an internal reference voltage.
• The error signal ,the difference between the input signal voltage and the reference voltage is fed to a chopper which converts d.c signal to an a.c signal. 13 March 2018 14
X-Y Recorder • The signal is then amplified in order to actuate a servomotor which is used to balance the system and hold it in balance as the value of the quantity being recorder changes.
13 March 2018 15 Digital Storage Oscilloscope • A digital storage oscilloscope is an oscilloscope which stores and analyses the signal digitally rather than using analogue techniques. • The input analogue signal is sampled and then converted into a digital record of the amplitude of the signal at each sample time.
13 March 2018 16 Digital Storage Oscilloscope • Basic advantage of digital operation is the storage capacity, stored information can be repeatedly read out, processing capability and analysis of the output.
• Furthermore, voltage and time scales can be easily changed after the waveform has been recorded, which allows expansion of the selected portions.
• Also cursor can be positioned at any desired point on the waveform and time & voltage values are displayed digitally on the screen
• Split screen capabilities enables easy comparison of the two signals. Digital Storage Oscilloscope • Pretrigger capability is also significant advantage. Slow read out of data is is possible for producing hardcopy with external plotters. • When more memory is needed, magnetic memory expansion is possible. • Analog input voltge can be sampled at adjustable rates. • But limited in bandwidth by the speed of the A/D Converters Digital Storage Oscilloscope
13 March 2018 19 Digital Storage Oscilloscope
13 March 2018 20 Digital Storage Oscilloscope • Initially the input signal is attenuated and it is then applied to the vertical amplifier. • The input, is then digitized by an analog to digital converter to create a data set that is stored in the memory .it can be available in the digital form also. • The stored digital data can be converted to analog signal and can be applied to CRO for displaying it. • The digital storage oscilloscope has three modes of operation: • 1. Roll mode ii) Store mode iii) Hold or save mode • Roll mode is used to display very fast varying signals, clearly on the screen. The fast varying signal is displayed as if it is changing slowly, on the screen Digital Storage Oscilloscope
13 March 2018 22 Smart Meter (AMI) Why electricity meters need an upgrade • With rising electricity prices, there is a need to give consumers greater control over their energy consumption. • New smart meter technology provides real-time information to customers through devices such as in-home displays and web portals, and provide half-hourly consumption data to electricity distributors – who then pass that i for atio o to the custo er’s electricity retailer.
• A smart meter is a new kind of gas and electricity meter that can digitally send meter readings to your energy supplier. This can ensure more accurate energy bills. Smart meters also come with monitors, so you can better understand your energy usage. • Smart meters use a secure national communication network (called the DCC) to automatically and wirelessly send your actual energy usage to your supplier. This means households will no longer rely on estimated energy bills, have to provide their own regular readings, or have meter readers come into their homes to read the meter. • Smart meters will also come with an in-home display. • This display gives the household real-time usage info, including kWh use and cost.
What are the benefits of having a smart meter? There are several benefits to smart meters: • More accurate bills Smart meters mean the end of estimated bills, the end of having to remember to provide meter readings and/or have a stranger come into your home to read your meter • Better understanding of your usage With the smart meter display, you can see the direct impact your habits and lifestyle have on your bill. This is particularly useful to prepayment meter customers, who can better track how their usage impacts their available credit. By making your energy usage easier to understand, you can make smarter decisions to save energy and money, including feeling more confident switching energy supplier. • Faster and easier energy switching Because your usage data is so easily accessible, the aim is to make energy switching as quick as just a half hour. • Bringing Britain's energy system into the 21st century The future is smart, and smart meters are part of the effort to create a smart grid, which is part of providing low-carbon, efficient and reliable energy to Britain's households. • Innovative energy tariffs Using the data collected on when and how households are using energy, suppliers can create more competitive time- of-use tariffs with cheaper prices for off-peak use.
How much does it cost?
• Your smart meter will be installed by your energy supplier at no charge to you. The cost of the roll out is covered already in your energy bill - the same way that installation and maintenance of traditional meters is. Advanced Metering Infrastructure (AMI) • One component of the grid that is being upgraded right now is the electric meter. Major electric utility companies in Michigan and across the United States are replacing existing electric meters with new Advanced Metering Infrastructure meters (smart meters). These meters wirelessly transmit electronic meter readings to your utility, virtually eliminating the need for on-site meter reading. The meters will also provide a host of other benefits.
Consumer Benefits
• Two-way communication between consumers and utilities comes with many advantages. The utility can monitor systems to ensure proper operation, functionality, and efficiency.
Locating blackouts and restoring power • Smart meters can notify an electricity distributor in real-ti e if a pre ise’s power is out. • These outage alerts can speed up power reconnection because the source of the problem can be pinpointed instantly, allowing repair crews to be prioritised appropriately and repairs to begin sooner. • Smart meters can then verify whether power has been restored to all meters