 ПОЗНАВАТЕЛЬНОЕ
| Text 9. Radio-Frequency Amplifiers
The functions of a radio-frequency amplifier are to increase the voltage ofthe radio-frequency (r. f.) signal and to secure the required selectivity of the receiver. The voltage applied to the input of a r. f. amplifier is from units to hundreds of microvolts depending on the sensitivity of the receiver. Before the signal reaches the detector it should be amplified a million times or more. Such voltage gain may be obtained only with the aid of several amplifier stages. A r.f. amplifier stage contains a valve or a transistor and a load, which is a resonant circuit tuned to the frequency of the signal applied to the input of the stage. This resonant circuit may be a signal tuned circuit or a band-pass filter. R. f. amplifiers in which single-tuned circuits serve as a load are known as tuned amplifiers. In case r. f. amplifiers employ band-pass filters for load they are called band-pass or filter amplifiers. Band-pass amplifiers have a nearly rectangular resonance curve. They are mostly fixed frequency amplifiers, i. e. their tuned circuits do not have to be retuned when the receiver is in operation. Band-pass amplifiers are widely used as i. f. amplifiers in superheterodyne receivers. In a band-pass amplifiers the anode load is a band-pass filter which may have widely differing circuit configurations and may be connected to the anode of the amplifier valve in many ways.
Notes
Text 11. Detection The process by which the signal being transmitted is reproduced from the radio-frequency currents present at the receiver is called detection, or sometimes demodulation. Where the intelligence is transmitted by varying the amplitude of the radiated wave, detection is accomplished by rectifying the radio-frequency currents. The rectified current thus produced varies in accordance with the signal originally modulated on the wave radiated at the transmitter and so reproduces the desired signal. Thus, when the modulated wave is rectified, the resulting current has an average value that varies in accordance with the amplitude of the original signal. In the transmission of code signals by radio, the rectified current reproduces the dots and dashes of the telegraph code and could be used to operate a telegraph sounder. When it is desired to receive the telegraph signals directly on a telephone receiver, it is necessary to break up the dots and dashes at an audible rate in order to give a note that can be heard, since otherwise the telephone receiver would give forth a succession of unintelligible clicks. The detection of a frequency-modulated wave involves two steps. First, the wave is transmitted through a circuit in which the relative output obtained from the circuit depends upon the frequency. The circuit output is then an amplitude-modulated wave since, as the frequency of the constant-amplitude input wave varies, the output will vary correspondingly. The resulting amplitude-modulated wave is then rectified. Notes
Text 13. Functions of Vacuum Tubes Although the applications of vacuum tubes are almost infinite, the specific functions that vacuum tubes can perform by virtue of their own properties are relatively few. It is these few fundamental functions and their combinations that give rise to the numerous applications. A list of the functions of vacuum tubes is bound to be an arbitrary one since the tube cannot function by itself without an associated circuit. However, some of the jobs that vacuum tubes can perform are so fundamental that they may be considered properties of the tube itself, independent of the associated circuits. The principal functions that may be performed by vacuum tubes are listed below. Rectification. — Vacuum tubes are able to convert alternating currents to direct currents. This is known as “rectification”. Rectification is an inherent property of vacuum tubes because current can flow in only one direction from a source of electrons. If a sinusoidal wave of voltage is applied to a vacuum tube of the right type, current will flow in only one direction, giving rise to a succession of half-wave pulses all of the same polarity. It is possible to connect another like tube to insert half-wave pulses of the same polarity between the pulses of the first tube. The average of these pulses constitutes a direct current; the other frequency components are rejected by a filter circuit. Rectification is important because electronic devices operate best on direct current, while power is usually generated and transmitted in alternating form. It is thus necessary to convert or rectify, the a- c power to d-c power. Amplification. — The amplification of voltage or power is the outstanding function that vacuum tubes are able to perform. With the exception of the mechanical torque amplifier, no other device can do anything like it. Strictly speaking, the vacuum tube does not amplify power but rather controls the flow of a relatively large amount of power from one source with a small amount of power to another source. The British use the expression “electric valve” for certain types of electron tubes. This term indicates the nature of the amplifying action. Oscillation. — The generation of high-frequency alternating currents, or oscillation, is another remarkable function that vacuum tubes can perform. Oscillation is obtained by causing part of the output of an amplifier to excite the amplifier and thus make the device self-excited and self-sustaining. Tubes can be built that will produce oscillations at frequencies as low as 1 cycle per sec, while other tubes can be built that will oscillate at frequencies as high as 60,000 me per sec. Frequency Conversion. —Vacuum tubes are able to shift the frequency of a wave. This they are able to do by an electrical “beat” action. Thus a wave of a given frequency can be mixed with a wave of another frequency in a vacuum tube, and among the products of the interaction is found the difference of the two frequencies. If one of the original waves had certain effects associated with it, these same effects are associated with the difference frequency. The beat action results from the nonlinear characteristics of the vacuum tube. Modulation. — The transmission of intelligence by radio waves or by certain types of wire telephone requires the use of frequencies higher than those audible. It is necessary to superimpose the audible frequencies upon the higher transmitted frequency. This superimposition is known as “modulation”. Modulation is best performed by vacuum tubes. Basically, modulation takes the form of varying some property of the r-f wave at the audible rate. The commonest form of modulation varies the amplitude of the r-f wave in accordance with the intelligence to be transmitted. This is known as “amplitude modulation”. Frequency modulation is also common. Detection. — Detection is the inverse of modulation and is sometimes known as “demodulation”. It is the process of extracting the intelligence from the modulated wave. In the case of amplitude modulation the detection may be effected by rectifying the r-f wave and then utilizing the average value of the rectified wave, since it follows the amplitude variations in magnitude. Detection of modulated radio signals is best performed by vacuum tubes over most of the range of radio frequencies. Light-image Production. — It is possible for vacuum tubes to convert part of their output energy into visible light. This is done in cathode-ray tubes in which a stream of electrons is caused to hit a fluorescent screen, causing light to be emitted. The cathode-ray tube can be used for viewing wave forms and for doing many other wonderful things, including the reproduction of visual scenes. The fundamental property involved here is the conversion of electrical energy into visual energy. Photoelectric Action. — Vacuum tubes can be made that will convert light energy into electrical energy. This is possible by virtue of the photoelectric effect, which is the emission of electrons from certain surfaces when illuminated with visual energy. The liberated electrons constitute an electric current whose measure is related to the frequency and intensity of the exciting light. Tubes making use of this principle are known as “photoelectric tubes”. The photoelectric tube is one of the tubes most extensively used in industrial-control systems. Notes
Text 14. Basic Tube Types Vacuum Diode The vacuum diode is a two-electrode vacuum tube. One electrode acts as an emitter of electrons and is called the “cathode”. The other electrode acts as a collector of electrons and is called the “anode” or “plate”. The emitter may be either directly or indirectly heated. In physical form the vacuum diode may vary from a small metal tube to a large glass rectifier tube. The most useful property of the diode is that it passes current only in one direction. This property makes the diode useful as a detector and as a rectifier for d. c. power supplies. Vacuum Triode A vacuum triode is a three-electrode tube containing an emitting electrode called the “cathode”, a control electrode called the “grid”, and a current-collecting electrode called the “anode” or “plate”. The emitting electrode may be an indirectly heated oxide cathode, an oxide-coated filament, or a filament of tungsten. The control electrode, usually in the form of a grid of fine wire, surrounds the emitter and is in turn surrounded by the plate in the commonest form of triode. By virtue of its proximity to the cathode the grid is able to influence the electrostatic field at the cathode to a greater extent than can the plate, and thus it is able to control the flow of current from the cathode. The grid is usually operated ona slight negative potential so that the electrons will pass between the grid wires without hitting the wires themselves. Triodes have their greatest use as power amplifiers. They are also used extensively in control applications wherever a small voltage is wanted to control an appreciable amount of current. Notes
Text 20. Fundamentals of Radar How Radar Works The design of a radar begins with consideration of its intended use, that is, the function to be performed by the radar as a whole. The uses generally divide into three categories: 1. Warning and surveillance of activity, including identification. 2. Aids to the direction of weapons, that is, gunfire control and searchlight control. 3. Observation of terrain echoes or beacons for navigation and control of bombing. There is nothing mysterious or complex about radiolocation. It rests on the foundations of ordinary radio theory, and is a technique based on the transmission, reception, and interpretation of radiofrequency pulses. Considered as a whole, it must be admitted that even the most elementary of radar equipment is difficult to visualize, but this is simply due to the fact that so many (normally) curious circuits and pieces of apparatus are gathered together under one roof. No particular circuit or detail of the equipment is in itself especially difficult to understand, and once the elements are known the complete assembly is no longer mentally unmanageable. The word “radar” is derived from the phrase “radio direction- finding and range”, and it may be more expressive than the older “radiolocation”, or it may not. Finding the position of an aircraft or a ship by means of radio covers a very wide field of electronic application, covers, in fact, the whole area of radio direction-finding (R. D. F.) from the elementary bearing-loop to the principle of the reflected pulse which represents the latest principle of the technique. The term will be used to cover only those methods of detection which depend upon the reflected pulse, the characteristic (by popular opinion) which distinguishes radar from all other methods of position- finding in that no cooperation is required on the part of the target. We shall not dwell, therefore, upon the older and more familiar methods which depend upon the reception at two or more points of a signal transmitted by the body under location itself. The actual equipments in use which employ the reflected pulse principle are greatly varied from the point of view of physical appearance, but their basic principles are the same. First, let us tabulate and briefly analyse the problem to be met. The aim of radar is to find the position of a target with respect to a fixed point on the ground — say the position of an aeroplane or a barrage balloon with respect to the radar equipment situated in a field a mile or so away: Three quantities must be
Notes
Text 22. Bearing The determination of bearing is not quite so easy as finding range, but it is, nevertheless, much simpler than the determination of elevation. Target bearing is determined by the use of special aerial arrays. Proud owners of portable broadcast receivers who regard their loop aerial as a “special” array, may find the bearing of the local B.B.C. station by suitable orientation of their equipment. Radar, requiring a somewhat more refined method, with corresponding accuracy, finds itself unable to rely on simple loops and generally uses such a system as that of the Slowcock array. This system consists essentially of two collinear horizontal half-wave dipoles with centres one wavelength apart connected to the receiver as shown in Fig. 8. When the line of the aerials is perpendicular to the horizontal direction of arrival of the reflected pulse, zero signal is presented to the receiver, even if the wave is arriving obliquely from above. If now the receiver moves slightly off bearing, the direction of arrival of the reflected signal departs from the zero-signal position and a small signal is presented to the receiving circuits, the phase of this signal reversing as the direction of it passes through that of “on bearing” or zero signal. Comparison of the phase of this signal with a “standard” signal received on another canal then makes it possible for the operator to determine to which side of the receiving array the target has moved and so enables him to return quickly to the zero signal position. In practice it is not convenient to work to a minimum, or null point, especially when the signal is being observed on a cathode-ray tube, and so special methods of presentation are adopted which in the main consist of either a maximum signal or the equality of two signals for the correct on-bearing position of the receiving array. There are many variations of this type of aerial array for special purposes, but most radar equipments depend on the above simple fundamental system. Notes
Text 23. Transistors, the Basic Mechanism Transistor action is the control of currents or voltages in one junction by the currents or voltages in another junction. This control is possible because of the minority and majority carriers flowing across the junctions being controllable. Transistor action can occur when we have two or more rectifying junctions in close proximity. In fact, all transistors make use of rectification at junctions within materials in one way or another.
All transistors have some features in common. They are generally small in size. The actual working volume of a transistor seldom exceeds a cubic millimeter. This is true even for high-power devices. There is a heat-dissipation problem to be faced in almost all transistor applications. In high-power applications, particularly, the heat-dissipating structure is many times the size of the device itself. The characteristics of transistors depend upon the operating temperature to a great extent, and special consideration must be given to the stability of transistor circuits as a function of temperature. The power dissipated in circuits will be large enough to cause large changes in the temperature of the transistor. In the case of the vacuum tube, temperature is not usually a primary circuit stability consideration since the tube is usually hot anyway because of the use of thermionic cathodes. As an aid in solving the temperature-sensitivity problem, new high-temperature materials are being developed. Germanium is good for the devices operating below about 90° C. Silicon can be used to about 200° C. There is no reason to believe that better materials cannot be developed.
Notes basic ['beisxk] — основний junction ['d3Ai)k/n] — з’єднання minority [mai'noriti] — меншість majority [ma'djonti] — більшість proximity [prok'simiti] — близкість rectification [^ectifi'kei/n] — детектування alloy ['геїоі] — сплав surface-barrier ['satfis baeris] — поверхова перешкода grown-junction — зрощуваний перехід to quench [kwentf] — гасити to melt — плавити diffused-base [di'fju:zd] — дифузійна база drift — зсув to exceed [ik'si:d] — перевищувати dissipation ^disi'pei/n] — розсіювання
Text 24. Radio Transmitters General Considerations. A radio transmitter is known to be essentially a device for producing radio-frequency energy that is controlled by the intelligence to be transmitted. A transmitter accordingly represents a combination of oscillator, power amplifiers, harmonic generators, modulator, power-supply systems, etc., which will best achieve the desired result. Commercial transmitting equipment is ordinarily mounted on a framework of structural-steel members fronted by a vertical metal panel containing the controls and meters necessary for adjusting and monitoring the transmitter. All equipment appearing on the panel is at ground potential, instruments which must be observed during adjustment or operation and which are not at ground potential being located behind the panel and viewed through windows. The steel frame is normally enclosed with wire mesh of some sort and is provided with doors that cut off the transmitter power when opened. This type of construction requires a minimum of floor space in proportion to the amount of apparatus involved, makes the transmitter accessible for inspection and repairing, and eliminates all hazard to persons. The design of most radio transmitters, particularly those intended for broadcast and short-wave transmission, is dominated by the need of maintaining the transmitted frequency as nearly constant as possible over long periods of time. In broadcast work two or more transmitters are commonly assigned the same carrier frequency, and in order to minimize the resulting interference it is essential that the carrier frequencies be as nearly as possible the same. The Microphone Transmitter. The microphone transmitter may be one of the ordinary carbon granule type. Without going into details, it will suffice to state here that such a microphone consists simply of an elastic diaphragm bearing against a mass of carbon granules enclosed in a suitable chamber, the carbon granules forming part of an electrical circuit. When the microphone is not being spoken into, the diaphragm remains stationary and exerts a constant pressure upon the carbon granules, the resistance of which remains, therefore, constant. On the other hand, when the diaphragm is set vibrating, as it is done by speaking into the microphone or through a noise or sound reaching it, the pressure exerted by the diaphragm against the carbon granules changes, and this change of pressure causes the resistance of the carbon granules to increase or decrease in accordance with the displacement of the diaphragm from its position of rest. When the microphone is not being spoken into, the alternator produces a high-frequency current of constant amplitude, i. e., an undamped current; the amplitude of this current is adjusted to the maximum by adjusting the inductance so as to make the natural frequency of the circuit equal to the frequency of the alternator. Now, assume, for the sake of simplicity, a vibrating tuning fork to be placed in front of the microphone. The harmonic vibrations of the tuning fork will bring about harmonic vibrations of the microphone diaphragm, and these will produce variations in the resistance of the microphone. Since no other part of the circuit is undergoing any change, it is plain that a variation of the microphone resistance will produce a corresponding variation in the amplitude of the high- frequency antenna current. Thus, when the diaphragm is displaced inwardly the resistance of the microphone and, therefore, of the entire alternator circuit, decreases, and the amplitude of the current supplied by the alternator must necessarily increase, the reverse taking place when the diaphragm is displaced outwardly. Notes
Text 25. Transistor Radio Frequency Amplifiers Like valve amplifiers a transistor r. f. amplifier may be of the tuned or of the band-pass variety. On long, medium and short waves, the transistor is usually connected into a common emitter circuit while in the VHF and UHF bands use is sometimes made of the common base arrangement. Transistor amplifiers differ from valve amplifiers in interstage coupling. Operation of a transistor amplifier is affected by the output resistance of the transistor, which is much lower than the output resistance of an amplifier valve. This is why transformer and tapped- coil coupling is used extensively in r. f. transistor amplifiers.
To eliminate a. c. feedback R3 is bypassed to earth by Cb. Should the operating point shift due to temperature changes it will be restored by the feedback voltage built up across R3 and applied to the transistor base. It should be noted however that in both configurations the tuned circuit may be connected to the collector circuit directly, provided the output resistance of the transistor is sufficiently high. Notes
Computing Technique Text 1. The Computer A computer is a machine that can take in information, perform different operations and provide answers. A computer can perform logical and mathematical operations such as addition, subtraction, multiplication, division, and some more complex mathematical operations. Logical operations deal with selecting, comparing, matching and so on meeting different needs of the users. All the operations of a computer are performed at high speed in some kind of language (marks or symbols). The computer has pervaded most fields of human activity and may well be the most important innovation of our age. Born out of the technology of communication, it is capable of handling enormous amounts of information at tremendous speeds. What makes it so potent is the fact that a single mechanism can perform any informa- tion-processing task. The same mechanism can control industrial processes, guide space vehicles or help to teach children. This diversity of tasks is made possible by the simple idea of the stored program. The trick is to control electronically the nature and sequence of arithmetical and logical processes that are themselves electronic. In other words, what determines whether an addition, multiplication or some other operation is executed, what determines the inputs of the operation and what determines the disposition of the result are not built into the machine but are part of the electronic process itself. A program is the enumeration of theses determining commands; it specifies the method used for the solution of a problem in detail. When the machine is in operation, both the commands and the numbers or symbols being processed are constantly being taken out of and put into a depository of information known as a memory. The commands, numbers or symbols needed in a processing task — known collectively as words — are stored in the memory, each with a certain “address”. The address identifies the stored word and determines a definite physical location within the memory device. The power and universality of programming arise from the capacity to address the memory selectively, that is, to direct a word into any address and to retrieve it in a very short time, regardless of how the address was previously used. Notes addition O'di/n] — додавання subtraction [sab'traekjn] — віднімання multiplication [.тліцріі'кеї/п] — множення
Text 2. Using the Computer The types of computers available are as varied as the types of musical instruments. Trying to teach someone to use a computer requires that both the instructor and the student have access to the same type of computer. It would be senseless for a piano teacher to try to teach someone to play a trombone. There is another similarity between trying to learn to play a musical instrument and trying to learn to use a computer: in order to learn to use either a specific computer or a specific musical instrument properly, you must practise on a daily basis. One strength is that it explains some of the differences likely to be found in computers and in computer applications and teaches some of the techniques necessary to help you more easily learn to use a computer. The biggest flaw in most computer systems is the instruction book. The instruction book for a computer system is primarily a reference document; when the user gets into trouble, he can discover by reading the book what he is doing wrong and what needs to be done to get the computer operating properly. An instruction book can also be a manual that instructs a new user, in a step-by-step manner, how to run a computer system. Unfortunately, most computer system instruction books take either one approach or the other. They are either excellent reference books, leaving much to be desired by the first-time user who simply wants to get the computer working, or are written to be how-to-start-the-computer cookbooks with glaring deficiencies that become apparent when the user experiences trouble with the system. Most users of a computer system routinely use only a very small part of the total features available to them. For example, one may have purchased a computer system that can compose music, write payroll checks, and trap burglars as they try to sneak in through the skylight. Although the computer can do all of these things if you buy the proper accessories for it, most users are interested in only one thing, such as having the computer only write payroll checks. Notes
Text 3. Peripheral Equipment The microcomputer has to communicate with the outside world, so that programs and data can be entered into its memory and processed information can be displayed or transmitted in some form to the microcomputer user. There are various types of peripheral equipment that may be attached to microcomputers including keyboards and paper tape readers for input, and visual display units (VDUs) and printers for output. Information may be output from the microcomputer on to magnetic tape or disk for storage and re-entered when required. Different sensors and actuators may be linked (interfaced) to the microcomputer for controlling instruments and machines. Keyboards A keyboard consists of a number of switches which are activated by pressure or simply by touching them. The keys are arranged as a matrix, so that the depression of any key can be detected by scanning the rows and columns of the matrix. Hardware may be used to sense which key has been pressed or this may be carried out by a software routine. The layout of the keyboard may be similar to that of the conventional typewriter or may be designed for particular users. Teletypewriters Teletypewriters may be used for a number of different purposes in computer systems. For example, they may be used as terminals to transmit and receive information over telephone lines or as input/ output devices directly connected to a computer. Teletypewriters transmit and receive information in serial form, that is, each character is converted to a bit-code, and then sent as a stream of serial data bits with start and stop control bits for each character. The characters have to be decoded when they reach the computer end. Teletypewriters and other terminals using telephone lines require modems (modulators-demodulators) at each end, to convert the data to a form suitable for voice transmission and vice versa. As well as having a keyboard, teletypewriters are fitted with a printing device, so that a hard copy of the information sent and received is available. Characters are printed one at a time by moving the block containing the characters across the paper from left to right. The selected character is pressed against a typewriter ribbon to give a solid shape. Speeds vary from about 10—30 characters/second. Teletypewriters may have paper tape stations for producing output on to punched paper tape. Notes
торкатися програмне забезпечення матриця апаратне забезпечення схема інформаційний біт
один за одним щоб зробити щільний відтиск перфострічковий прилад
Text 4. Computers on Wheels The mountain road was violently zig-zagging, but the driver did not slow down. He seemed to be more concerned with two timetables — that of the bus and school lessons. The bus had to arrive at a country school in time for the next lesson. Personal computers are mounted in the bus’s interior where basic instruction is given under the school curriculum in information science and computer technology. Children from village and town schools are thus learning to operate computers. It is one of the forms of implementing the countrywide programme for computer knowledge among students. At present, the fundamentals of information science and computer technology are studied in nearly 60,000 secondary schools throughout the country. The subject has been included in the curricula of the tenth and eleventh forms. As an experiment, computer lessons sometimes start at an earlier age, even at the elementary school. The authors of the experiments have developed teaching methods that allow computer operation to be combined with strengthening the oral count habits, developing the so-called sense of numbers, improving the standards of logic and mathematical thinking. For example, a mathematical dictation for solving textual problems. Teachers know that with the conventional methods the better part of a maths lesson is spent on putting down the solutions of problems (as a rule, children write slowly) and calculations. The logic part of the solution takes very little time. With computer equipment, this can be done efficiently and with the entire class participating. The teacher slowly dictates the problem, while the children are not writing but listening attentively and thinking about the development. After a repeat, they immediately work out the problem on a computer or a calculator. The computer enables them to check the solution. In the second part of the lesson, a pupil comments on the line of reasoning. Using this method, the pupils of experimental classes can solve eight to ten problems in 15 to 20 minutes. Notes
Text 5. Programming a Computer Each family of processors has its own instruction set which is likely to differ from that of other processors. This means that a particular processor is only capable of understanding its own set of instructions in binary code. The computer’s memory can be considered as consisting of a number of cells capable of storing binary patterns representing program instructions or data. Each of these cells is uniquely numbered so that reference can be made to particular memory cells, either to select a program instruction or data, or to write data into a certain memory cell. As an example of how programs are written in a computer’s own code (machine code), it will be assumed that two numbers are held in memory cells 5 and 6, that these are to be added together, and the result stored in memory cell 8. The addition will be performed in a storage location called the accumulator, so the first instruction needs to load one of the numbers into the accumulator. The second instruction adds the other number to the number in the accumulator, which will then contain the sum of the two numbers. The third instruction stores the contents of the accumulator in the required memory cell. The binary codes for these instructions for a typical processor are shown in Table. Table. Machine Code Instructions
Notes
Text 6. The Robot’s Nervous System Robots, in order to perform many functions, need a nervous system and organs of sense as well as a brain. A human being has to have eyes and ears, a nose, a mouth and a sense of feel. Depending on the task it is to perform, a robot can have any of these built into it. A robot’s eyes, for example, are generally made up of photoelectric cells. A robot eye can consist of one cell, or of hundreds of cells placed close together. A one-cell eye isn’t able to do much more than tell the difference between light and dark, while some of the more complex ones are able to see colour and detect movement. Robots can be taught to hear various types of sounds. Usually they are made so that they can hear only those sounds which are important to them. For instance, a robot designed to hear the sound of a jet aircraft would have no reason to hear the voice of a bird. Robot ears are better than human ears for a given single function because they are not distracted by unimportant sounds. Robot hearing is possible because sound is a form of energy. It comes in waves. Some sound waves have high frequency, others have low frequencies. A robot can be adjusted to detect differences in frequency. If sounds of a given frequency are important to a robot’s job, it acts on them. Otherwise the brain ignores the sound. Robot noses can detect different odours because the elements that make up those odours change the composition of the air that carries them. Robot noses are adjusted to analyse air passing through their nostrils and from the air composition tell what that air smells like. Robots feel in the same way that humans do. Tiny wire fingers can go across a surface and, from the way the surface pushes the wires around, the robot can tell whether the surface is smooth or rough. Robots can also tell the difference between two temperatures. Another kind of robot feel sensor can feel the exact temperature more accurately than any thermometer. Notes
Text 7. Menu System To help a person control the bookkeeping system by computer, the computer can be programmed with what is known as a menu system. This menu system for a program or for data selection enables the person running the computer to see a list of the things he can do next. Each item on the menu can, if necessary, select its own menu; and that menu can, in turn, call still other menus. For example, the person who is trying to manage a company’s accounting system may sit down at the business computer and be shown a menu that would let him select accounts payable, accounts receivable, general ledger, inventory, or payroll. The computer operator might then select payroll, whereupon the computer would then respond with the payroll menu, showing items necessary to guide the computer operator. One such item might be “enter hours worked”. Selecting this item would allow the computer operator to input to the computer the number of hours that each employee had worked during the pay period. Another item might be “print paychecks”. Once all of the information had been input and the computer operator was satisfied that the information was correct, the computer could be directed to actually print the employee paychecks. Notes
Text 8. Input, Process, Store, Output There are four steps that any computer uses in doing its job. These are (1) inputting of data into the computer, (2) processing of the data that has been input, (3) storage of data, and (4) production of some kind of useful output. In business computers, this four-step process is very easy to see. In order to produce a bill for a customer, we would have to input the information about what the customer bought. Once all of this information had been input, the computer would process this information and would print the information for the customer’s bill. Throughout this cycle, the computer would be storing (1) the data that had been input, (2) the data produced during intermediate processing steps, and (3) the data being printed out. Apart from processing data, computer systems are being increasingly used to store data; such storage has the advantage of allowing data to be rapidly retrieved. In manufacturing, computers are used to control robots. If you think about it, any robot has to use some sort of a computer as the basis for its “intelligence". If we were to build a robot to be used in the assembling of automobiles, and if our robot had the specific task of mounting wheels on the car, the instructions for this process would be input into the computer. In addition, the robot would still have to be able to determine where the car and the wheel were. Various types of sensors, such as a television camera, would enable the robot to “see” the position of the wheel and the car. In this case, we would not have to type information into a computer for the robot to act. We do have to have some means of getting the data into the computer, like a television camera. If we were to build this robot correctly, it would use the television camera to tell where the car was, where the wheel was, and even where the lug nuts were. The television camera would be the input. The process would be the calculations required to determine how to get the wheel on the car, and the output would be the robot’s response to these calculations: mounting the wheel on the car, putting on and then tightening the lug nuts, and checking to see if the tire were properly mounted. The basic steps — input, store, process, and output — would be taking place with our robot even though no data was typed into the robot’s computer. Notes
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Text 9. Input-Output System The input-output system consists of three parts: 1. Input and output units. 2. Auxiliary units. 3. Peripheral equipment. The input and output units are internal functional parts of the computer. The auxiliaries are links between the computer and the outside world. The peripheral equipment is needed to make the operation of the computer more efficient and more meaningful. The input unit consists of an input register plus associated input control circuits. The input unit receives signals from the control unit whenever a word or a group of words is to be entered into the machine. The input unit also makes incoming information more palatable than the rest of the computer. The output unit consists of an input register plus associated output control circuits. The output unit receives signals from the control unit whenever a word or a group of words is to be removed from the machine. The output unit also modifies information so it can be more readily applied to the output auxiliaries. Auxiliary devices either feed information into the computer or take information out of the computer. These auxiliary devices are of two general types: direct analog as well as digital, linked with external storage. The direct-digital device communicates directly between man and machine. It may take the form of a keyboard for manually entering instruction or data words. It may be a printer which prints results of computations onto paper or a group of display lights on the control panel indicating the contents of internal registers. The analog input auxiliary accepts analog information and converts it to digital form for entry into the input register. The analog output auxiliary receives digital information from the output register and converts it to analog form. The first device is called an analog-to-digi- tal converter, the second being called a digital-to-analog converter. The input auxiliary linked with digital storage reads information from external digital storage and feeds it into the input register. The digital auxiliary accepts information from the output register and writes it into external storage. Examples of such input and output auxiliaries are magnetic tape, punched paper tape, and punched-card readers and writers. The peripheral equipment is concerned mainly with external digital storage. Recorders are used by operators to place information into external storage. An example is a device which writes words onto magnetic tape when keys of a keyboard are operated. Converters transform information stored in one form to information stored in another form. An example is the punched-card-to-magnetic-tape converter. Communication devices are used to send information to or from external storage. An example is a teletype. The input and output units are integral portions of the digital computer. Under direction of the control unit they determine the shape, sequence, speed, and time of arrival of bits and words as they are transferred between the computer and auxiliary devices. Notes
register ['гесізшз] — лічильник; регістр content ['kontant] — зміст; суть entry ['entri] — вхід to convert [kan'va:rt] — перетворювати punched [рлт/t] — перфорований analog-to-digital converter — аналого-цифровий перетворювач punched-card reader — прилад для зчитування перфокарт punched-card-to-magnetic- — прилад, який передруковує з перфо- tape converter карти на магнітну стрічку Text 10. Memory The electronic “memory” of a computer is a depot to store numbers and instructions. From this depot they are sent for processing to “the mathematical mill”. The results obtained are returned to the “memory”. It may be said that the history of progress in high-speed computers coincides with the history of the improvement of their “memory”. Quite recently the electron tube “memory was considered highspeed “memory”. Next the ferrite-core “memory” was produced. The working speed of most up-to-date computers holds up to ten million bits. To increase the capacity and data production speed are the most important aims of contemporary computer construction. Tunnel diodes, thin magnetic films — these so called microminiaturization elements are used to construct the “memory”. Memory consists of three elements: storage, read and write circuits, and address selection. But any storage system requires these three elements. What distinguishes a memory from other types of storage? To answer this question, let us look at different classes of storage. Storage may be classified according to size. There is bit storage, as exemplified by the flip-flop; there is word storage, as exemplified by the register and counter; and there is multiword storage which is exemplified by systems of bulk storage. Storage may be classified according to whether it is external or internal. External storage exists outside the computer; it is not a fundamental part of the computer. Internal storage is an integral part of the machine; without it the computer cannot function. Storage may be classified according to whether it is fixed or erasable. The contents of fixed storage cannot be changed. The contents of erasable storage can be changed — it can be written into. To be considered memory, storage must be: 1. Bulk storage. 2. Internal. 3. Erasable. Obviously one bit or one word cannot constitute memory; we need a device which can store many words. Internal storage implies that there is ready and quick communication between memory and the other functional units of the computer. Erasibility means 2-way access to words in memory, in as well as out. To summarize, we may say that memory is accessible bulk storage which may be written into as well as read from. External storage is used in the input and output systems. Fixed storage may be used in the control unit for storage of nonchangeable programs in special-purpose computers. Modern science considers that many branches of knowledge depend to a great extent on the solution of the problem of human memory and on the levels of development of artificial computer memory. Notes
Text 11. Automatic Translator Another machine that we can foresee would be used for translating from one language to any other. We can call it an automatic translator. Suppose that you want to say “How much?” in Swedish. You dial into the machine “How much?” and press the button “Swedish”, and the machine will promptly write out “Hur mycket?” for you. It also will pronounce it, if you wish, for there would be little difficulty in recording on magnetic tape the pronunciation of theword as spoken by a good speaker of the language. The machine could be set to repeat the pronunciation several times so that the student could really learn the sound. He could learn it better, probably, by hearing it and trying to say it than he could by using any set of written symbols. Notes to foresee [fo:'si:] — передбачати automatic [^ta'maetik] — автоматичний to pronounce [pre'nauns] — вимовляти pronunciation [ргз^лпві'еі/п] — вимова Text 12. Universal Electronic Computer Without calculating machines normal life of modern society and continued progress in science and technology would be impossible. But even wi |
measured in order to define the position of the aeroplane or the barrage balloon: first, the slant range, the length of the most direct line drawn from the radar site to the target; second, the angle of bearing, i.e. which point of the compass the target occupies; third, the angle of elevation. Fig. 6 should make these points clear for you. When the target is an aeroplane, these three quantities are continuously varying so that the problem of position-finding is somewhat complicated by the fact that the radar equipment has to “follow” as well as find. In the case of barrage balloon, things are not quite so difficult, and the three important factors may be found at leisure.
There is a large variety of transistorlike devices, some examples being the transistor diode, which may be of the alloy, surface-barri- er, grown-junction, melt-quench, diffused-base, drift, or point-contact types. There are tetrode transistors, field-effect transistors and many more. It seems likely that there will soon be at least as many transistors types as there are vacuum tubes types.
The stability of the operation of a transistor amplifier largely depends on the position of the quiescent operating point. To stabilize this point the circuit employs negative direct-current feedback provided by R3 (Fig. 9) connected in the emitter circuit. Such an arrangement is similar to the current feedback arrangement in valve circuits.
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