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THE UNIVERSITY OF DANANGCOLLEGE OF FOREIGN LANGUAGES
DEPARTMENT OF ENGLISH FOR SPECIFIC PURPOSES----- -----
Nguyễn thị cẩm tú, M.Ed
ENGLISHIN
ELECTRONICS AND TELECOMMUNICATIONS
Danang 2008
THE UNIVERSITY OF DANANGCOLLEGE OF FOREIGN LANGUAGES
DEPARTMENT OF ENGLISH FOR SPECIFIC PURPOSES----- -----
NGUYÃÙN THË CÁØM TUÏ, M.Ed.
ENGLISHIN
ELECTRONICS
Danang 2008UNIT 1 INTRODUCTION TO CONDUCTIVITY
Reading and Comprehension CONDUCTORS, INSULATORS AND SEMICONDUCTORS If we connect a battery across a body, there is a movement of free electrons towards the positive end. This movement of electrons is an electric current. All materials can be classified into three groups according to how readily they permit an electric current to flow. These are: conductors, insulators, and semiconductors. In the first category are substances which provide an easy path for an electric current. All metals are conductors, however some metals do not conduct well. Manganin, for example, is a poor conductor. Copper is a good conductor, therefore it is widely used for cables. A non-metal which conducts well is carbon. Salt water is an example of a liquid conductor. A material which does not easily release electrons is called an insulator. Rubber, nylon, porcelain and air are all insulators. There are no perfect insulators. All insulators will allow some flow of electrons, however this can usually be ignored because the flow they permit is so small. Semiconductors are midway between conductors and insulators. Under certain conditions they allow a current to flow easily but under others they behave as insulators. Germanium and silicon are semiconductors. Mixtures of certain metallic oxides also act as semiconductors. These are known as thermistors. The resistance of thermistors falls rapidly as their temperature rises. They are therefore used in temperature-sensing devices.
EXERCISE A Rephrasing
Rewrite the following sentences, replacing the words in italic with expressions from the text above which have similar meanings:
1. The flow of free electrons is an electric current.2. Materials in the first group are called conductors.3. Materials which provide a path for an electric current are conductors.4. All insulators permit some flow of electrons.5. Germanium sometimes acts as an insulator and sometimes as a conductor.
EXERCISE B Contextual Reference
What do the pronouns in italic in these sentences refer to?1. All materials can be classified into three groups according to how readily they permit an electric current to flow. (a) three groups(b) all materials(c) free electrons2. All insulators will allow some flow of electrons, however this can usually be ignored because the flow they permit is so small.
(a) electrons (b) electrons in flow
(c) all insulators3. Under certain conditions they allow a current to flow easily but under others they behave as insulators. (a) conductors(b) semiconductors(c) insulators4. These are known as thermistors. (a) metallic oxides(b) semiconductors(c) mixtures of certain metallic oxides5. They are therefore used in temperature-sensing devices. (a) thermistors(b) semiconductors(c) metallic oxides
EXERCISE C Checking facts and ideas
Decide if these statements are true or false. Quote from the passage to support your decisions.
1. Electrons flow from positive to negative2. Copper provides an easy path for an electric current.3. All metals are good conductors.4. All good conductors are metals5. Air is not a perfect insulator6. Rubber readily releases electrons.7. Semiconductors are mixtures of certain metallic oxides.
8. The resistance of a thermistor is higher at low temperatures than at high temperatures.
Word study 1DESCRIBING SHAPES
Study these nouns and adjectives for describing the shapes of objects:
Shape Noun Adjective Shape noun Adjective2 dimensional 3- dimensional
circle circular
sphere spherical
semi-circle semi-circular cylinder
cylindrical
square square tube tubular
rectangle rectangular rectangular
Lines Edges
straight rounded
curved pointed
When something has a regular geometric shape we can use one of the adjectives from the table to describe it.
EXAMPLE
a square waveWhen the object has no recognized geometric shape but does resemble a well-known object or a letter of the alphabet, it may be described in one of the following ways :EXAMPLE
an H-shaped antenna a saw-tooth wave
EXERCISE DNow describe the shapes of the following objects as completely as possible:(a)(c)(b)(d)
1. a ceramic capacitor 2. Transformer laminations
3. an electrolytic capacitor 4. an antenna
5. a magnet 6. a cable conduit
7. a carbon brush 8. a apacitor
9. a motor pole shoe 10. a resistor Word study 2
WORD FORMATION 1- SUFFIXESWhen you are reading, you will come across unfamiliar words. It is often possible to guess the meanings of these words if you understand the way the words in English are generally formed.An English word can be divided into 3 parts: a prefix, a stem, and a suffix. Pre- means ‘’before”, a prefix, therefore is what comes before the stem. A suffix, on the other hand, is what is attached to the end of the stem. Both of them are referred to affixes.Suffixes change the part of speech of the word. For example, -or added to the verb conduct gives the noun conductor.SUFFIXES MEANINGS EXAMPLES
Noun- forming suffixes:-ance
state resonance, resistance-ence quality
of interference, existence-er /-or a person who / a thing which oscillator,
amplifier-ation the act
of modulation, attenuation-ness condition of
opaqueness, brightness-ion action /
state transmission, expansion-ing
activity interlacing, scanning-ment state /
action measurement, movement-ity state / quality
conductivity, directivity -ian pertaining to
electrician, technician-ism condition / state
magnetism, synchronism-dom
condition freedom-ship condition / state
relationship, friendship-age
state leakage, shortage-ful containing lots
of handful, teaspoonful Verb- forming suffixes:-ize /-ise industrialize, synchronize-ate to activate, calculate
-fy make rectify, amplify-en shorten, harden Adjective- forming suffixes:-al have structural, axial, horizontal-ar quality circular, rectangular-ic / -ical of electrostatic, logical-able / -ible capable of being demountable, accessible-ous /- ious like, full of ferrous, obvious-ful characterized by useful, colourful-less without wireless, colourless-ish like childish, bookish-ed having coloured, integrated-ive quality of photosensitive, defective-ing making or doing
signalling, processing EXERCISE EIdentify the suffixes included in the following passages1. In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard. However, the system was not launched publicly until late in the 1990s.2. A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV. It was commonly understood only a digital system could possibly bring desired results; however, nothing such had yet been developed. Language study 1
DESCRIBING POSITION AND CONNECTION
When describing the position of a component or how it is connected in a circuit, phrases of this pattern are used:
be + past participle + prepositionEXAMPLES 1.The tuning capacitor IS CONNECTED ACROSS the coil. 2. The semiconductor rectifier IS MOUNTED ON the heat sink.
EXERCISE F Now complete each sentence using an appropriate phrase from this list:
wound round located withinconnected across applied tomounted on connected towired to connected between
Polepiecescore
1. The bulbs are . . . . . . . the battery 2. The core is . . . . . the pole pieces.27pF
3. The 27 pF capacitor is . . . . . . the 4. The antenna is . . . . . the coil.collector and the base.C1
rotorshaft
feedback5. Feedback voltage is . . . . . the 6. The rotor is . . . . . the shaft.base of the transistor through C1
core
-
+
7. The coil is . . . . . an iron core. 8. The negative pole of the battery . . . . . . . earth.
Language study 2RELATIVE CLAUSES
Study these sentences:1. Starter motor brushes are made of carbon.2. The carbon contains copper.
Both these sentences refer to carbon. We can link them by making sentence 2 a relative clause.
1+2 Starter motor brushes are made of carbon WHICH CONTAINS COPPER.The relative clause is in capital. Note that THE CARBON in sentence 2 becomes WHICH. Study these other pairs of sentences and note how they are linked:
3. Consumers are supplied at higher voltages than domestic consumers.4. These consumers use large quantities of energy.
3+4 Consumers WHO USE LARGE QUANTITIES OF ENERGY are supplied at higher voltages than domestic consumers.
5. 33 kV lines are fed to intermediate substations.6. In the intermediate substations the voltage is stepped down to 11 kV.
5+6 33 kV lines are fed to intermediate substations WHERE THE VOLTAGE IS STEPPED DOWN TO 11 kV.
EXERCISE GNow link these sentences. Make the second sentence in each pair a relative clause:
1. The coil is connected in series with a resistor.The resistor has a value of 240 ohms.
2. The supply is fed to a distribution substation.The supply is reduced to 415 V in the distribution substation.
3. Workers require a high degree of illumination.The workers assemble very small precision instruments.
4. Manganin is a metal.This metal has a comparatively high resistance.
5. The signal passes to the detector.The signal is rectified by the detector
6. A milliammeter is an instrument.The instrument is used for measuring small currents.
7. Workers require illumination of 300 lux.The workers assemble heavy machinery.
8. Armoured cables are used in places.There is a risk of mechanical damage in these places.
Language study 3PRONOUN LINKS BETWEEN SENTENCES
When we link sentences together, or into paragraphs, repeated nouns are usually pronouns.
EXAMPLE
1. A short circuit occurs in a transformer.2. The short circuit may cause overheating.3. The overheating may further damage the insulation.
1+2+3: When a short circuit occurs in a transformer, IT may cause overheating. THIS may further damage the insulation. When there may be misunderstanding, or when the repeated noun comes a long time after its first mention, the full noun is used.
EXAMPLE
First the pole shoes and coils are drawn out of the yoke. Then the coils are removed from them and new coils are fitted over them. Next they are refitted inside the yoke and located by lightly tightening the fixing screws. Finally they are tightened fully and their terminals are soldered.
Compare this version where the full nouns have been kept:
First the pole shoes and coils are drawn out of the yoke. Then the coils are removed from the shoes and new coil fitted over the shoes. Next the shoes are refitted inside the yoke and located by lightly tightening the fixing screws. Finally the screws are tightened fully and the new coil terminals are soldered.
EXERCISE HNow replace the repeated nouns in this paragraph with suitable pronouns where there is no likelihood of confusion.
A transformer is a device which changes the magnitude of an ac voltage. The transformer consists of a primary coil to which the input is applied, and a secondary coil from which the output is obtained. The coils are insulated and wound round a former. The coils have a core of soft iron on which the former is mounted. The core is made from many thin sheets or laminations. The sheets are oxidized so that the sheets are insulated from each other. Oxidizing the sheets reduces eddy losses.
Information transferMATHEMATICAL SYMBOLS
EXERCISE I Make sure that you understand some mathematical symbols used in electrical engineering and electronics. Then write out the following expressions in full. EXAMPLE is equal to E over R.
a. P = I2 x Rb.
c.
d.
e. E = IRf. Frequency stability 0.04% / oCg.
h.
i. collector dissipation 12 miliwatts Guided writing
DESCRIBING A DIAGRAM STAGE 1 Sentence buildingJoin the following groups of sentences to make ten longer sentences. Use the words printed in italic at the beginning of each group. You may omit words and make whatever changes you think are necessary in the word order and punctuation of the sentences.
1. orCircuit can be protected from excessive currents by a fuse.Circuit can be protected from excessive currents by a circuit breaker.2. howeverA fuse is the simplest and cheapest protection.For accurate and repetitive operation a circuit breaker is used.3. whichThe simplest circuit breaker consists of a solenoid and a switch with contacts.The contacts are held closed by a latch. 4. thus energizingThe current from the supply line flows through the switch and solenoid coil.This energizes the solenoid.5. which, thereforeAt normal currents the pull of the solenoid on the latch will not overcome the tension of the spring.The spring holds the latch in place.The switch remains closed.6. ifThe current rises to a dangerous level.The pull of the solenoid on the latch increases.
7. andThe increased pull overcomes the latch spring tension.The increased pull pulls the latch towards the solenoid.8. whichThis releases the switch contacts.The switch contacts are pulled apart by a spring.9. asThe circuit is now broken.The unit is protected.10. WhenThe fault in the supply or unit is put right.The latch can be reset.
STAGE 2 Diagram labelling Label this diagram with the following:Solenoid, latch, switch contacts, latch spring, switch spring abcdefrom supplyto unit
SummarizingSTAGE 1 Comprehension
Study this passage carefully and answer the questions which follow: SUPERCONDUCTIVITY
The resistance of metals varies with their temperature. When they get hot, their resistance increases. When they cool, their resistance falls. The resistance of some metals and alloys steadily decreases as their temperature is lowered, then falls suddenly to a negligible value at temperatures a few degrees above absolute zero (-273 o C ). In other words, these materials have almost no resistance to an electric current at very low temperatures. They become almost perfect conductors. This is called superconductivity. It occurs only with certain materials, for example lead, and only at very low temperatures. The practical applications of superconductivity are limited because of the very low temperatures required. A number of uses, however, have been proposed. If a current is induced by a magnetic field in a ring of superconducting material, it will continue to circulate when the magnetic field is moved. In theory this could be made use of in the memory cells of computers. Memory cells made of superconducting materials could store information indefinitely. Because of the zero resistivity of the cells, the information could be retrieved very quickly, as fast as 10 -8
seconds. Ninety per cent of the total losses in modern transformers is due to the resistance of the windings. Transformers could be made with windings cooled to the low temperatures at which superconductivity occurs. The resistance of the windings would be zero and the transformer would be almost ideal. Similarly a 100 % efficient electric motor has been proposed using the magnetic field of superconducting coils.
1. Name a superconducting material.2. When do materials exhibit superconductivity?3. Why are the practical applications limited?4. What applications have been proposed?5. What advantages would a memory cell made of a superconducting material have?6. How efficient would transformers and motors be which used superconductivity?
STAGE 2 Summarizing
Complete this summary of the passage using your answers to Stage1:
Some materials, for example . . . . . . , become almost perfect conductors at . . . . . .The applications of superconductivity are limited because . . . . . . .Possible uses are . . . . . . . .A superconducting memory cell would allow information . . . . . . .A transformer or motor using superconductivity would be . . . . . . . UNIT 2 SEMICONDUCTOR DIODES
Reading and ComprehensionSEMICONDUCTOR DIODESIf two crystals of a semiconductor material, one of p-type and one of n-type, are joined together, a pn junction is formed. This junction can be used as a rectifier and is known as a pn junction diode.604020
1.02.0Reverse voltage (V)Forward voltage (V)
Fig. 2.1 Figure 2.1 illustrates what happens when a voltage is applied across a silicon PN junction diode. The first quadrant of the graph shows the characteristics of the diode when the source is connected with the positive to the p-side of the junction and the negative to the n-side. In other words, the diode is forward biased. With forward bias, the current at first increases slowly. When the applied voltage reaches about 600 mV, the current rises rapidly. The diode is then a good conductor. The current will continue to rise with increased voltage but eventually a point will be reached where the diode is destroyed by heat. The third quadrant shows the characteristics when the source is connected with the positive to the n-side and the negative to the p-side. When the diode is reverse biased, there is almost no current flow. The junction is therefore a good rectifier: it conducts well in one direction and almost not at all in the other. However there is a small reverse leakage current. This leakage current remains substantially constant until what is known as breakdown voltage (Vb) is reached.
At this point there is a sharp increase in the reverse current. This sudden increase in current is called the Zener effect. Normal diodes are never operated in the breakdown region but Zener diodes are designed to make use of the breakdown phenomenon. Because any slight increase in voltage beyond the breakdown point causes a large increase in current, Zener diodes are often used as a kind of overspill to protect sensitive circuits from fluctuations in the power supply. EXERCISE A Meaning from context
Select a word from the three alternatives given which is most similar in meaning to the word in italics as it is used in the passage.
1. characteristics (a) typical behaviour (b) voltage figures (c) graph 2. substantially
(a) almost (b) greatly (c) hardly
3. sharp (a) slight (b) steep (c)
cutting4. phenomenon
(a) voltage (b) effect (c) result
5. fluctuations(a) rises and falls (b) increases (c) failures
EXERCISE B Recognizing rephrasing
Find a sentence in the passage which is similar in meaning to each of these sentences:1. The positive of the source is connected to the p-side of the diode and the negative to the n-side.2. When a forward voltage is applied across the diode, there is , at first, only a slow rise in current.3. The diode allows current to flow freely.4. If a reverse voltage is applied to the diode, it conducts badly.5. There is almost no change in leakage current until the reverse voltage reaches breakdown point.
EXERCISE C Checking facts and ideas
Decide if these statements are true or false. Quote from the passage to support your decisions.
1. The first quadrant of the graph shows the characteristics of the diode in forward bias.2. For forward voltages over 600 mV, the diode conducts well.3. When the source is connected with the negative to the n-side and the positive to the p-side, the diode is reverse biased.4. When a reverse voltage is first applied, a diode conducts badly.5. Zener diodes are never used beyond breakdown point.
Word study
WORD FORMATION 2 - PREFIXESPrefixes usually change the meaning of the word. For example, non- makes the meaning of the word negative. PREFIXES MEANINGS EXAMPLES
Prefixes of Negative and positive meanings:un-
unimportant, uninterestingin- not,
inconvenient, inexpensiveim- not good enough impossible,
impurityil- not connected with illegal, illogicallyir-
irregular, irrelevantnon-
non-conductor, non-flammablemis- bad, wrong
mislead, mismatchdis- opposite action disassemble,
dischargeanti- against anti-
virus, anti-corrosionde- reduce, reverse decode,
demodulationunder- too little
underload, underheatover- too much
overload, overcurrentre- do again
reheat, refine Prefixes of Size:semi- half, partly semi-conductor, semi-finalhemi- / demi- hemisphere, equi- equal equiaxialmaxi- / macro- big maxicomputermini- / micro- small minicomputer Prefixes of Location:inter- between, among interface, intermediate
super- over superconductor, supersonictrans- across transform, transmitex- out exclude, exposureextra- beyond extraordinary, extrapolationsub- under / secondary submarine, substation, subtotalinfra- beyond infrared, infrasonicunder- below underground, underloaded Prefixes of Time and Order: pre- before preheat, prestoreprime- first prime-ministerpost- after post-war, post-graduate Prefixes of Numbers: mono- one monolingual, monochromaticbi- two bicycle, bifilartri- three triangle, trichromoscopequad- four quadrangle, quadruplepenta- five Pentagon, pentagrid
EXERCISE DIdentify the prefixes included in the following passage The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are:- Small size and minimal weight, allowing the development of miniaturized electronic devices. - Highly automated manufacturing processes, resulting in low per-unit cost. - Lower possible operating voltages, making transistors suitable for small, battery-powered applications. - No warm-up period for cathode heaters required after power application. - Lower power dissipation and generally greater energy efficiency. - Higher reliability and greater physical ruggedness. - Extremely long life. Some transistorized devices produced more than 30 years ago are still in service.
- Complementary devices available, facilitating the design of complementary-symmetry circuits, something impossible with vacuum tubes. - Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications. Language study 1
1. WRITING INSTRUCTIONS Simple instructions use the infinitive.
EXAMPLES1. Measure the collector current.2. Switch off the supply.3. Do not solder transistors without a heat-shunt.
Study these instructions for an experiment to measure the total resistance of resistor in series using the circuit in Figure 2.2.ABAV
Fig. 2.2
1. Use a high-resistance voltmeter and a low-resistance ammeter.2. Connect R1 across AB.3. Close the switch and adjust the rheostat until both meters show almost full scale deflection.4. Take simultaneous readings of both voltage and current.5. Calculate R1 by the formula 6. Repeat this for R2.7. Connect R1 and R2 in series across AB.8. Calculate the total resistance using the same formula as before.9. Tabulate the results.
2. DESCRIBING AN EXPERIMENT
Use the present passive to describe an experiment.EXERCISE E Make a description of the experiment above by rewriting each instruction in the present passive.
EXAMPLE1. Use a high-resistance voltmeter and a low-resistance ammeter.A HIGH-RESISTANCE VOLTMETER AND A LOW-RESISTANCE AMMETER ARE USED.
3. REPORTING AN EXPERIMENT
Use the past passive to report an experiment.EXERCISE FMake a report of the experiment above by rewriting each instruction in the past passive.
EXAMPLE
1. Connect up the apparatus as shown in Figure 2.2.THE APPARATUS WAS CONNECTED UP as shown in Figure 2.2.
EXERCISE G Writing instructions 2.
Study this description of how batteries are charged:
The filler plugs are removed and the battery is connected to the charger. It must be ensured that the correct polarity is observed and good connections are made. The charger id then switched on. The charger is switched off when the battery has been fully charged. The specific gravity of a sample cell is checked. The filler plugs are replaced and the battery left to cool before use.
Now begin the list of instructions for how to charge a battery. Begin like this:1. Remove the filler plugs.
Language study 2
DESCRIBING GRAPHSGraphs are a common way of giving information. They allow a great deal of data to be presented easily in visual form. Study the words and phrases that are commonly used to describe the rate of change Direction Verb Noun Adjective AdverbUp climb
go upincreaserise
increaserise
slightgradualsteadyslow
slightlygraduallysteadilyslowly
Down declinedecreasedropfallgo down
declinedecreasedropfall
sharpsuddenfaststeep
sharplysuddenlyfaststeeply
Level (do) not changeremain constantkeep unchanged
no change
We can describe the change in two ways:1. The voltage increases.2. There is an increase in the voltage.
We can make our description more accurate like this:3. The voltage increases rapidly.4. There is a rapid increase in the voltage.
EXERCISE H Describing diode characteristics
Complete this description of the current- voltage characteristics of a silicon diode. Use the passage and Figure 2.1 to help you.
At first, when a forward voltage is applied, ........................ .When the forward voltage has reached about 600 mV, ............................... . If the forward voltage is further increased, ........................ . ........................ only a very small leakage current flows. When the breakdown voltage is reached, ......................... After the breakdown point, any further increase in reverse voltage causes .........................
Language study 3
TIME CLAUSES
Time clauses relate two actions in time. In this section, we will study clauses relating:
1.R ()
2. Simultaneous actions T (0C)
Study this graph. It represents two actions which happen at the same time, i.e. two simultaneous actions.Action (i) The temperature risesAction (ii) The resistance rises We can link two simultaneous actions using as.EXAMPLE AS the temperature rises, the resistance rises.We will represent simultaneous actions like this:
Action (i)Action (ii)
2. Actions in immediate succession
240 VM
Study this circuit and note how action (i) is followed immediately by action (ii).Action (i) The switch is closed.Action (ii) The motor starts. We can link actions in immediate succession using when or as soon as.EXAMPLE
WHEN the switch is closed, the motor starts.We will present actions in immediate succession like this
action (i) action (ii)
3.I mA
V V
P6. Action and limit
This graph shows an action and its limit. The action is limited.Action : The current rises steadily.Limit : Point P is reached. We can link an action and its limit using until.EXAMPLE
The current rises steadily UNTIL point P is reached.We will represent this relationship like this : actionlimit
4. Actions in sequence
In this case, action (i) is followed by action (ii)
Action (i) The signal has been detected.Action (ii) The signal is amplified. We can link actions in immediate succession using after.EXAMPLE
AFTER the signal has been detected, it is amplified.
Remember that we represent actions in sequence like this : action (i)action (ii)
EXERCISE I Time clausesNow link these pairs of actions using time clauses. The diagrams indicate the relationship between each pair.
1. the voltage increases the current increases
2. the current continues to rise the diode is destroyed by heat 3. a reverse voltage is applied very little current flows 4. the signal is rectified the signal is amplified5. the leakage current remains constant the breakdown voltage is &nb sp;&n bsp; reached
6. the applied voltage reaches the current rises rapidly about 600 mV
7. the magnetizing current is saturation point is reachedincreased 8. the current drawn by the current in the Zener the load increases decreases Information transfer
READING TRANSISTOR CHARACTERISTICS
The chart below shows the characteristics of a number of transistors manufactured by Mullard Ltd.
1 2 3 4 5 6 7 8 9Type Polarity P tot at T mb
I CM IC max BVCBO BVCEO BVEBO
(W) (OC) (A) (A(d.c.) (V) (V) (V)
BD124 N 15 60 4 2 70 45 6BD131/ 3 N 11 60 6 3 70/90 45/60 6BD132 P 11 60 6 3 45 45 4BD135/7/9 N 6.5 60 1.5 0.5 45/60/100 45/60/80 5BD138/8/40 P 6.5 60 1.5 0.5 45/60/100 45/60/80 5
10 11 12 13 14 15 16 17
Type hEF at VCE
IC VCE(sat) at IC IB fT at IC
(V) (A) (V) (A) (A) (MHz) (A)BD124 25min 5 2 0.50 typ 2 0.2 120 typ 0.25
BD131/ 3 20 min 1 2 0.9 max 2 0.2 60 min 0.25BD132 20 min 1 2 0.9 max 2 0.2 60 min 0.25
BD135/7/9 25min 2 0.5 0.5 max 0.5 0.05 250 typ 0.05BD138/8/40 25min 2 0.5 0.5 max 0.5 0.05 75 typ 0.05 Study this description of the characteristics of one of these transistors and make yourself familiar with the English meaning of each of the abbreviations typed in the chart. The characteristics have been numbered in both chart and subscription to help you.
The BD 124 (1) is a silicon NPN (2) transistor manufactured by Mullard. It dissipates a maximum power of 15 watts (3) at a mounting base temperature of 60oC (4) . The peak collector current it can pass is 4 amps (5). The maximum permitted dc current flowing out of the collector terminal is 2 amps (6). The collector-base breakdown voltage, with the emitter disconnected, is 70 volts (7), The collector-emitter junction would break down at 45 volts (8). The voltage at which the emitter-base junction would break down is 6 volts (9). None of these breakdown voltages should be exceeded. The dc current amplification factor is at least 25 (10) when measured at a collector-emitter voltage of 5 volts (11) and a collector current of 2 amps (12). The collector-emitter saturation voltage is typically 0.50 volts (13). The collector current at saturation voltage is 2 amps (14) and the base current 0.2 amps (15). These characteristics are important in switching circuits. They represent the conditions under which the transistor is on. The frequency at which the current gain would be reduced to 1 is typically 120 MHz (16). The collector current at this frequency would be 0.25 amps (17). EXERCISE J Describing transistor characteristics
Now complete this description of the BD 132:
The BD 132 is a silicon (a) . . . . . transistor. It dissipates (b) . . . . . at a mounting base temperature of 60oC. The peak collector current is (c) . . . . . The maximum dc (d) . . . . . is 3 amps. The breakdown voltages for the collector-base, (e) . . . . . and emitter-base junctions are (f) . . . . . , 45 V, and (g). . . . . respectively.
Dc current gain is at least (h) . . . . . when measured at a collector-emitter voltage of (i) . . . . . and a (j) . . . . . of 2 amps.
A collector-emitter voltage drop of a maximum of a 0.9 volts exists when a (k) . . . . . of 2 amps and a base current of (l) . . . . . amps flow. These are the saturation condition for this transistor.
The frequency at which the current gain would be reduced to 1 is (m) . . . . . .The collector current at this frequency would be (n) . . . . . Guided writing
WRITING EXPLANATIONSSTAGE 1 Writing explanations 1A good explanation allows the reader to link his knowledge with that of the writer. A bad explanation either over-estimates the reader’s knowledge with the result that he cannot understand it, or under-estimates the reader’s knowledge so that he is bored.Study the following explanations. They all try to explain why conductors are coated with plastic.
1. Conductors are coated with plastic because plastic is an insulator.
Explanation 1 is effective if the reader knows what an insulator is.
2. Conductors are coated with plastic because plastic is an insulator. An insulator does not readily release electrons.
Explanation 2 is effective if the reader knows that current is carried by electrons.3. Conductors are coated with plastic because plastic is an insulator. An insulator does not
readily release electrons. Free electrons carry current and thus no current can pass through the plastic.
Explanation 3 is effective for the reader who does not know what an insulator is, nor how current is carried.
Explanations often involve answering how and why questions.EXAMPLES
1. Copper is a good conductor (why ?) BECAUSE it readily releases electrons.2. Use a heat shunt when soldering sensitive components (why ?) SO THAT they are not
damaged by heat.3. The current flowing through a resistor, can be calculated (how ?) BY DIVIDING the
voltage by the resistance.4. The RF section of a receiver is sometimes screened (why ?) TO PREVENT interference
from other parts of the receiver. EXERCISE KNow answer the WHY ? and HOW ? questions following each of these statements. Use the information given below.
1. Soldering wire contains flux (why ?) to . . . . . . .2. When a current flows through the filament of a light bulb, it gives off light (why?)
because . . . . . .3. The value of a resistor can be calculated from the colour bands on the body (how?)
by. . . . . .4. Manganin wire is used for the elements of an electric wire (why ?) because of . . . 5. Sensitive equipment is protected by fuses ( why ?) so that . . . . .6. Light bulbs may contain rare gases (why ?) to . . . . .7. Curved pole shoes are fitted to meter magnets (why ?) so that . . . . .8. When a relay is energized, sets of contacts are pushed together or apart ( how ?) by
means of . . . . .(a) The pole shoes help form a radial magnetic field.(b) The filament becomes incandescent.(c) The equipment is not damaged by excess current.(d) The gases prevent the filament burning up.(e) The flux prevents the surfaces being joined from oxidizing.(f) A relay contains a moving armature which controls the contacts.(g) Manganin has a higher resistance than most metals.(h) The colour code is used to determine the value of a resistor.
STAGE 2 Writing explanations 2
With the help of a suitable textbook, write your own explanation of the operation of one of the following:
1. a relay2. a microphone ( any type )3. a transformer4. a dc motor
Summarizing
MODULATIONSTAGE 1 Reading for specific information
Find all the answers to these questions in the passage which follows. Work as quickly as you can. Try to ignore information which will not help you to answer the questions.
1. What is modulation?2. Which three quantities of a wave can be modulated?3. Why is frequency modulation better than amplitude modulation?
We can only communicate information by radio waves by changing the wave in some way. This change is known as modulation. The simplest form of modulation is to turn the wave on and off. This method was used in the early days of radio for telegraphic signals. The wave was stopped and started to represent the dots and dashes of the Morse code by means of a telegraph key.
Speech and music produce audio frequencies which cannot be transmitted directly. But they can be used to modulate radio waves. The modulated radio wave is then transmitted. When it is received, the wave is demodulated and the original audio-frequency signal is recovered. The high frequency radio wave acts only to carry the audio-frequency signal and is called the carrier wave. The audio-frequency signal is termed the modulating signal.
A wave has three quantities: amplitude, frequency and phase. Any of these quantities can be modulated. The two commonest methods of modulation are amplitude modulation, AM, and frequency modulation, FM.In amplitude modulation, the amplitude of the carrier wave is changed according to the amplitude of the modulating signal. The frequency of the carrier is kept constant. Figure 1 represents part of an audio-frequency signal, which might be generated by a microphone. Figure 2 represents a radio wave of much higher frequency. Figure 3 shows the same radio frequency wave after it has been modulated by the audio-frequency signal in Figure 1.Fig. 2 Fig. 1Fig. 3
In frequency modulation, the amplitude of the carrier wave is kept constant, but the frequency is varied in proportion to the amplitude of the modulating signal. Frequency modulation has several advantages over amplitude modulation. The most notable is that reception is less likely to be disturbed. This is because atmospheric disturbances and ‘noise’ generated in the receiver itself result in a change in the amplitude of the received signal. However, changes in only the frequency would distort the modulated information.
In FM sound broadcasting, the limit of modulation is usually 75 kHz above and below the frequency of the unmodulated carrier wave. In other words, FM broadcasts spread 75 kHz either side of the carrier frequency. This is one reason why FM stations broadcast in the VHF band (30-300 MHz), where stations can be spaced more than several hundred kilohertz apart unlike the medium frequency bands where spacings of only 9 to 10 kHz are common.
STAGE 2 Recognizing rephrasing
Now read the whole passage carefully. Each of these sentences summarizes part of the passage. Identify the lines summarized.
1. In FM the frequency of the carrier wave is modulated according to the amplitude of the modulating signal. (lines . . . . . . ..)2. Audio frequencies cannot be transmitted. (lines . . . . . . ..)3. The amplitude, frequency and phase of a wave can be modulated. (lines . . . . . . ..)4. FM broadcasts are in the VHF band partly because FM stations require greater spacing. (lines . . . . . . ..)5. The carrier wave is demodulated by the receiver and the audio-frequency signal recovered. (lines . . . . . . ..)6. No information can be communicated by radio waves without modulating them. (lines . . . . . . ..)7. In AM the amplitude of the carrier wave is modulated according to the amplitude of the modulating signal. (lines . . . . . . ..)8. Stopping and starting the wave is the simplest method of modulation. (lines . . . . . . ..)9. FM is better than AM because there is less interference. (lines . . . . . . ..)10. Audio frequency can be used to modulate high frequency radio waves which can then act as carriers of the audio-frequency signal. (lines . . . . . . ..)
STAGE 3 Summarizing
Put the sentences in Stage 2 in the correct order and use them to make a paragraph summarizing the passage. You may add words of your own to make a good paragraph. Make sure no information is repeated unnecessarily. UNIT 3 ALARM SYSTEMS Reading and Comprehension 1
Fig. 3.1. Alarm system on window and door
DETECTION DEVICES
Magnetic switchesThese are used on windows and doors. A magnet mounted on the moving parts of the window or door trips a switch mounted on the frame when the window or door is opened. Break detectorsThese are fitted on the inside surface of glass in windows and doors. Some use a thin metal foil which is glued around the edge of the glass: if the glass is broken the foil breaks too. Others are vibration sensors, and respond to the shock of the glass being broken. Pressure matsThese are fitted under the carpet - at the bottom of the stairs, for example. The pressure of someone stepping on them causes two thin metal plates inside to come in contact, setting off the alarm. Because they’re constantly being walked on, pressure mats can get ‘tired’ quite quickly, and should be regularly tested and replaced if necessary. Motion sensorsThese may use passive infra-red, ultrasonic, or microwave energy to detect movement within their range. EXERCISE A Study the diagram above (fig.3.1) and try to answer these questions
1. What does this diagram show a circuit of?2. How many detection devices does it show? Name them.3. What warning devices does it show?4. Why is the control box switch operated with a key?5. How does the system work?6. What problem is there with this circuit?
EXERCISE B Explain briefly how the device works.
1. door switch 3. pressure mats2. window foil 4. passive infra-red detector
Reading and Comprehension 2HOW TO IMPROVE THE ALARM SYSTEMWe can make the simple alarm circuit more effective by including some of these features.Entry and exit delaysThese mean you won’t set off the alarm when leaving or returning to the house. On the better systems, the delays are adjustable. An audible warning during the delay period is a useful reminder. Automatic cut-offThis will stop the alarm after it has sounded for a set time, so that the noise doesn’t go on for hours if you are not there to reset the system. in better systems, the alarm automatically resets at the end of the alarm time.
Tamper protectionThe control panel incorporates sensors which will trigger the alarm if a burglar tries to force the box open. Battery backupThis means the alarm will continue to work in a power cut, or if an intruder disconnects the mains supply.
EXERCISE C Match each action with its consequence. Then identify the device or feature described. For example: Action Someone moves within its range. Consequence: It detects the movement. Device: Motion sensor
Action Consequence1. A burglar disconnects the supply.2. The glass is broken.3. A door is opened.4. A window is opened.5. You’re not there to reset the system.6. A burglar tries to force the alarm open.7. Someone step on them.
a. A magnet on the moving part trips a switch.b. Tamper sensors trigger the alarm.c. The alarm continues to operate on batteries.d. Two thin metal plates come in contact.e. The foil breaks too.f. A magnet on the door trips a switch on the frame.g. The alarm stops after a set time.
Word study COMPOUND NOUNSThe language of engineering in English contains an ever-increasing number of compound nouns, that is, a group of two or more nouns which act as a single noun.Examples: circuit breaker address bus bar code scanner control systemIt is important to be able to recognize how such compounds are formed in order to understand what they mean.
The exact relationship between the words depends on the particular expression, but all these expressions have one thing in common: the last word in the chain says what the thing is, while the preceding word or group of words describe the thing. So when we read compound nouns, we have to start with the last word and work backwards.Example:
A circuit breaker is (a device) used to break a circuit.
A large number of possible meanings can be expressed by compound nouns. For instance, the first noun or group of nouns can tell us what the second noun is made of, what it is for, or what it is part of.
1. Material: the first noun tells us what the second consists of.Examples:
- a silicon chip (a chip made of silicon)
- a ferrite switch (a switch made of ferrite)2. Function: the first noun tells us what the second is for.Examples:
- an input device (a device for inputting)- a battery charger (a device for charging battery)
3. Part: the second noun refers to a part of the first noun.Examples:
- a monitor screen (the screen of a monitor)- a computer keyboard (the keyboard of a computer)
4. Activity or person: the second noun refers to an activity or person related to the first noun.Examples:
- a computer programmer (a person who programs computers)- grid emission (the emission - of electron or ion - from a grid - of an electron tube)
5. Multiple nouns: sometimes a compound noun will join together with one or more other nouns to give an expression that has three or four words. In such cases, it is important to examine the expression very carefully to break it into its constituent parts. The secret, as always, is to read the expression from the back towards the front.Example: 4 3 2 1
a document image processing program (a program which processes images of documents)
NOTE: Some expressions are written separately, while others are joined by hyphens. There are no clear rules for this. Sometimes you will see the same expression written in different ways in different text.
EXERCISE D Make short simple explanations of the following items
1. shock absorber2. frequency band3. circuit board4. pressure regulator5. power switch
6. temperature sensor7. document sorter8. fuse carrier9. rectifying circuit10. voltage transformer
EXERCISE E Give names to:
1. a program which processes data2. a unit that holds magnetic disks3. the information about the configuration of a network4. a system which transmits (signals), or a system of transmission, using fibre optics5. the rate of transmission of data, or the rate of transmitting data6. a circuit, or a device which converts analog signals to digital signals
Language study 1 IF-SENTENCES
Study this action and its consequence:Action: A burglar tries to force the alarm open. Consequence: Sensors trigger the alarm.
We can link action and consequence like this:1. If a burglar tries to force the alarm open, sensors trigger the alarm.2. If a burglar tries to force the alarm open, sensors will trigger the alarm.3. Sensors will trigger the alarm if a burglar tries to force the alarm open.
EXERCISE F Complete these sentences with a suitable or consequence.
1. If pressure mats are constantly walked on, ..........................2. If you fit an exit delay, ..........................3. If your system doesn’t have an automatic cut-off, ..........................4. If a burglar walks in front of a motion sensor, ..........................5. Vibration sensors will respond if ..........................6. Tamper sensors will trigger the alarm if ..........................7. A magnet on the moving part trips a switch if ..........................8. The alarm stops after a set time, ..........................
EXERCISE G Complete the sentences using unless and your knowledge of engineering
1. Unless the ignition is switched on, a car cannot..........................2. Unless there is current flowing in the primary coil of a transformer, there will be ..........................in the secondary coil.3. Unless the power switch is .........................., the washing machine will not start.4. Unless the doors are.........................., a lift will not operate.5. Unless a signal from the satellite is amplified, it can not..........................6. Unless electrical equipment is earthed, it may be ..........................
Language study 2
REDUCED TIME CLAUSESStudy these two actions:
Action 1: Ground waves pass over sand.Action 2: Ground waves lose energy.
We can link these actions to make one sentence, using a time clause: 1+2 When ground waves pass over sand, they lose energy.Because the subject of both sentences is the same - ground waves - there is a shorter way we can use to link the actions: When passing over sand, ground waves lose energy.When + -ing shows that Action 2 happens during the same period as Action 1.
Now study these two actions: Action 3: The sky wave strikes the earth. Action 4: The sky wave bounces back again.Again we can link these actions to make one sentence, using a time clause: 3+4 When the sky wave strikes the earth, it bounces back again.We can link the actions in a shorter way: On striking the earth, the sky wave bounces back again.On + -ing shows that Action 4 follows immediately after Action 3.EXERCISE H Link these pairs of actions. Use short ways when this is possible.
1. a. The switch is closed.b. Currents flows through the primary of the transformer
2. a. The radar signal strikes a plane.b. The radar signal is reflected.3. a. A cell discharges quickly.b. A cell may become hot.4. a. The TV receives signals from the remote control.b. The TV follows your instructions.5. a. The radar receives the reflected signal.b. The signal is compared with the transmitted signal.6. a. Microwave signals strike a high building.b. Microwave signals are deflected7. a. The alarm detects an intruder.b. The alarm triggers an audible warning.8. a. The remote control button is pressed.b. The television set changes channel.
Information transfer
UNDERSTANDING A DIAGRAM Study the following text and the diagram.The three stages of a simple alarm system are shown as follows
........................
............................
.............................
The first stage is a sensing device that changes its resistance when it detects a particular from of energy. For example, a microphone may be used to detect sound, a thermistor to detect heat, or an LDR (light dependent resistor) to detect light. The second stage is an electronic switch. In its simplest form, this could be a single transistor. The transistor switches between cut-off and saturation as the input resistance changes. The third stage is an output transducer which is switches off and on by the electronic switch. The output transducer could be a buzzer, a light, or a relay which operates a more powerful circuit. An example of a simple alarm circuit is shown in the figure below.
Fig.3.2
The LDR forms a potential divider with the variable resistor RV1. When light falls on the LDR, its resistance decreases. This causes the base voltage of the transistor and the bias current to increase. The transistor switches on there is a rapid rise is the collector current until the transistor goes into saturation. The increased current cause the relay to operate and switch on the output circuit. The sensitivity of the input can be adjusted using RV1.
In a similar way, the relay is de-energized when the light source is removed from the LDR. A large back EMF, which would destroy the transistor, could be generated across the relay. To prevent this, a diode is connected in reverse bias across the relay. Writing Study this diagram, which explains the operation of automatic doors. Then link each set of statements below using words or phrases of your own to make your own explanation. Omit unnecessary words and make any other changes required.
1. Automatic doors are used in places such as airports, supermarkets, and hospitals.Traditional doors would be a nuisance in these places.2. Automatic doors are fitted with a microwave sensor.The sensor detects movement.3. The doors are switched onA microwave transmitter sends out a microwave beam.4. The beam is in a semicircular pattern.The doors open when you approach from any angle.5. The microwaves are reflected back to the sensor.
The reflected microwaves are analysed by a microprocessor.6. A person or object moves forwards the doors.The waves are reflected back to sensor at a different frequency.
7. The microprocessor detects this change. The microprocessor instructs the motor to open the doors.8. The doors are fitted with a time-delay mechanism.
The doors remain open for about four seconds before closing again.9. A person remains standing in the doorway.
A safety beam prevents the doors from closing.
UNIT 4 HIGH DEFINITION TELEVISION
Reading and ComprehensionIn Europe, the USA , and Japan , the race is on to produce a new generation of television sets. These new sets will be larger than today’s models, possibly with 100-centimetre flat screens. Picture quality will be excellent, crisp, and without flicker, as good as those we are used to seeing in the cinema. Sound quality too will be superb, thanks to digital multitrack transmissions. By the turn of the century such sets may be offering programmes in a choice of languages as they will be equipped with eight sound tracks.
In Europe , the term HDTV is used. In the USA , the more generic term ATV, Advanced Television, has been adopted. The Japanese, who were the first to start work on the new
technology, in 1974, called their system Hi-Vision. Whatever name is used, these new sets share certain features.
The picture is displayed using more lines per frame. This means that they provide clearer, more detailed, high quality images. The picture can be displayed on large, wide screens which are flicker-free. They also provide very high quality three-dimensional sound output.
A wider range of frequencies can be used to transmit each HDTV channel. This is because they can be transmitted at high frequencies which are virtually unused at present. These wide frequency ranges make it possible to transmit digital, rather than analogue signals. Digital processing can then be used in the receivers to provide almost perfect pictures even when the strength of the input signal is low. A computer could also be used to produce special effects.
Since not everyone is convinced of the need for such high quality TV systems, the move towards HDTV is likely to be very gradual. The first HDTV receivers will need to be able to process both the old and the new transmissions and, throughout the world, agreement will have to be reached on new transmission standards.
EXERCISE AStudy these graphics. Note ways in which high definition television will be different from existing sets. Complete the following table as the example: Features Existing TV High definition TVNo. of lines 625 1,250
Word study CIRCUIT SYMBOLSIn electrical engineering and electronics, components in a circuit are in the form of symbols. When we look at a symbol of a component, we need to know its function. EXERCISE B Label the following circuit symbols and match them with the appropriate functions in the list
a. varies capacitance in a circuitb. rectifies alternating currentc. adds resistance to a circuitd. measures very small currentse. breaks a circuit
f. protects a circuitg. varies the current in a circuith. steps AC voltages up or downi. receives RF signalsj. measures voltages
Language study 1 EXPRESSING THE CERTAINTYWhen we are confident about something in the future and less confident about others, we can use the following ways:
1. Using modal verbs might, can, could2. Using adverbs probably, possibly, certainly3. Using the structure Subject + be + adjective + THAT-clause / infinitive
EXERCISE CHow likely are these developments in the next few years? Make statements about each development using the certainty expressions.Example: Most houses in your country will be cleaned by electronic robots.
I think it’s unlikely that most houses in my country will be cleaned by electronic robots. It’s possible that some houses will use them.
1. Vinyl records will not be made.2. Most families in your country will have CD players.3. Most families in your country will have MD players.4. Most families in your country will have DCC players.5. Computers will understand and respond to your spoken language.6. Cars will be electronically guided through cities.7. Most teaching will be done by computers.8. Most families in your country will have HDTVs.
Language study 2 REASON AND RESULT CONNECTIVES Study these sentences:
1. Copper is used for cables.2. Copper is a good conductor.
Sentence 1 tells us what copper is used for. Sentence 2 tells us why it is used.Sentence 1 provides a reason for sentence 1. We can link a statement and a reason using because. 1+2. Copper is used for cables BECAUSE it is a good conductor.
When the reason is a noun or a noun phrase, we use because of.EXAMPLE
The motor overheated BECAUSE OF dirt in the air gap.
3. The flow of electrons through an insulator is very small.4. The flow can be ignored.
Sentence 4 is the result of sentence 3. We can link a statement and a result using therefore.3+4. The flow of electrons through an insulator is very small, THEREFORE it can be
ignored.
NOTE: A comma is used before therefore. EXERCISE D Now link these ideas using BECAUSE or THEREFORE.
1. Soft iron is used in electromagnets.Soft iron can be magnetized easily.
2. The voltage is 250 V and the current 5 A.The resistance is 50 V.
3. PVC is used to cover cablesPVC is a good insulator.
4. Transistors can be damaged by heat.Care must be taken when soldering transistors.
5. Capacitance is usually measured in microfarads or picofarads.The farad is too large a unit.
6. Output transistors are mounted on a heat sink.Output transistors generate heat.
7. It is easy to control the speed of dc motors.Dc motors are used when variable speeds are required.
8. A cathode-ray tube screen glows when an electron beam strikes it.The screen is coated with a phosphor.
Information transfer
COMBINATIONAL LOGIC
The decision-making circuits used in modern computers are mainly composed of combinations
of digital switching circuits known as logic gates. Fig. 4.1 shows the logic symbols and truth
tables for some basic gates.
AND
NAND
A B out A B out
0 0 0 0 0 1
0 1 0 0 1 1
1 0 0 1 0 1
1 1 1 1 1 0
NOT OR
A out A B out
0 1 0 0 0
1 0 0 1 1
1 0 1
1 1 1
Fig. 4. 2 Basic logic gates
The output of each gate depends on the combination of its inputs. This is known as combinational
logic. The output for all possible inputs is shown using a truth table. The truth tables show that the
output of an AND gate is only high (i.e. logic level 1) when all its inputs are high. The output of a
NAND gate, however, stays high unless all its inputs are high. The output of a NOT gate (also
known as an inverter) is always the opposite of its input.
Computers use ICs which contain a number of logic gates on one chip. An IC pin-out diagram
shows the arrangement of the gates and the function of each pin on the chip (see Fig. 4.2).
Vcc 4B 4A 4Y 3Y 3B 3A
1A 1B 1Y 2Y 2B 2A GND
14 13 12 11 10 9 8
1 2 3 4 5 6 7
quad 2 input NAND gatesTTL 7400 (CMOS 4011)
Fig. 4.3 An IC pin- out diagram
The number of ICs used in computer, i.e. the chip count, can be reduced by connecting NAND gates together to form other types of gates (see Fig. 4.4).
Fig.4.4 How NAND gates can be used to make basic logic gates.
The number of components in an IC is indicated by its scale of integration as shown in table 1. The IC shown in Fig.4. 3 is an SSI device but microprocessors used in computers are VLSI or SLSI devices.
Table 1
Scale of integration Abbreviation No. of active componentsSmall scale integrationMedium scale integrationLarge scale integrationVery large scale integrationSuper large scale integration
SSIMSILSIVLSISLSI
1 to 1010 to 102
102 to 103
103 to 104
104 to 105
There are two common families of logic ICs used in computers. TTL (transistor-transistor logic) ICs use bipolar transistors to form each gate whereas CMOS (complementary metal oxide semiconductor) ICs use field effect transistors (FETs). The different characteristics of each family determine which will be used in a particular computer (see Table 2). For example, TTL ICs are used in large, high-speed computers and CMOS ICs are better for battery - powered portable computers.
Table 2
Properties TTL CMOSSupply voltageSupply currentPower dissipationSwitching speedInput impedance
+ 5V 60.25 %mAmWfastlow
+ 3V to + 15VmAmWrelatively slowhigh
EXERCISE E Answer the following questions 1. What terms are used in the text for each of the following?a. a digital switching circuitb. the output of each gate depending on the combination of its inputsc. the number of ICs used in a computerd. an indication of the number of components used in an IC2. What is shown bya. a truth table?b. a pin- out diagram?3. What is another name for a NOT gate?4. What are the two common families of logic ICs?5. What do these abbreviations stand for?a. TTL b. VLSI c. CMOS d. MSI6. Which of these statements are TRUE for CMOS ICs?a. They contain bipolar transistors.b. They contain field effect transistors.c. They are particularly suitable for use in battery- operated portable computers.d. They are particularly suitable for use in large, high- speed computers.
EXERCISE F Logic GateComplete these statements with the help of the truth tables in Fig. 4.2. For example, in the case of an AND gate:
a. When A and B are low, the output is low.b. When A is low and B is high, the output is low.1. AND When A is high and B is low, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. NOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , the output is high.3. OR When A and B are high, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. NOT When A is high, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5. NAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., the output is low.6. NAND When A is high and B is low, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7. AND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., the output is high.8. NAND When A and B are low, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EXERCISE G Explaining a process control systemStudy the diagram below. It shows how an industrial process is controlled using logic gates. With the help of the diagram, complete the blanks in the explanation which follows. Each blank may be one or more words.lowhighcorrectsatisfactorycorrect
memorymotorswitchsupplyhopperpressureemptyoffonstorereset
Fig. 4.5 Control system using logic gates
A motor controlling the flow of aluminium blanks to a hydraulic press is switched on only under these conditions :
1. The power is on.2. The supply voltage is 1.........................3. There are 2 ......................... aluminium blanks in the hopper (store).4. The 3 ......................... in the hydraulic press is correct.Information on these four conditions is fed into an 4 ......................... as all four conditions
must be satisfied for the motor to run. When 5 ........................., the output from the AND gate is high. This is fed into the store input of the 6 ......................... unit to provide a continuous signal to operate the motor.
The motor must stop if any one of these conditions occurs :1. The power is 7 .........................2. The 8 ......................... rises.3. The hopper is 9 ......................... 4. The 10 ......................... drops.
Information on each of these conditions is fed through a 11 ......................... . When the input is low, 12 ......................... . The output from each NOT gate is fed to an 13......................... . When any of the four inputs to the OR gate is high, the output 14......................... . When this is fed to the memory reset, it interrupts the continuous signal to the motor. The motor is switched 15
......................... and the flow of aluminium blanks to the press thus 16 ......................... .Writing
TELEVISION DISPLAYSTAGE 1 Reading and comprehensionFind the answers to these questions by studying the text and diagrams below
1. What controls the movement of the spot of light across a televêion screen?2. What name is given to the rapid movement of the spot back across the screen to the start
of the next line?3. How many lines are used to build up a frame in present European television systems?4. What happens to a screen if the frame is not scanned at least forty times per second?
TELEVISION PICTURES A television picture is built up gradually by moving a spot of light across and down a screen in a raster pattern.
The video signal causes the brightness of the spot to vary in proportion to the intensity of light in the original image. The movement of the spot across the screen is controlled by the line scan signal. Each time the spot reaches the right side of the screen , it is blanked and moved rapidly back to the left side ready to start the next line. This rapid movement back to a starting position is known as flyback. Each complete image or frame requires a minimum of 500 lines to give a picture of acceptable quality. The present European TV system uses 625 lines per frame. The movement of the spot down the screen is controlled by the field scan signal. When the spot reaches the botom of the screen, it is blanked and moved rapidly back to the top of the screen. The frame must be scanned at least forty times per second to prevent the screen from flickering. The present European TV system has a frame scan rate of 50 Hz. The video signal contains line and field sync pulses to make sure that the TV receiver starts a new line and a new frame at the same time as the TV camera.
To allow the video signal to be transmitted using a smaller range of frequencies, each frame is transmitted in two separate halves, known as fields. The first time the spot travels down the screen it displays the first field, which consists of the odd- numbered frame lines. The second time the spot travels down the screen it displays the second field, which consists of the even- numbered frame lines. Combining two fields in this way is known as interlacing. Although the fields are displayed one after the other, it happens so quickly that the human eye sees them as one complete picture.
STAGE 2 Linking facts and ideasLink each set of statements, using words or phrases of your own to make an explanation of how a television picture is composed. Omit unnecessary words and make any other changes required.
1. A television picture is built up gradually.This is done by a moving spot.2. The spot strikes the television screen.The phosphor coating on the screen emits light.The light varies in brightness according to the intensity of the original image.3. The spot reaches the right side of the screen.The spot is blanked.The spot is moved rapidly back to the left side in a movement called flyback.4. The present European system sweeps the screen in a series of lines.There are 625 closely- spaced lines.Using 625 lines ensures a good quality picture.5. The movement across the screen is controlled by the line scan signal.The movement down the screen is controlled by the field scan signal.6. The scan rate must be greater than 40 Hz.A lower scan rate would cause the screen to flicker.7. Sync pulses are added to the video signal.The sync pulses ensure that the TV camera and TV receiver start a new line and frame at the same time.8. The build up of the screen happen very quickly.The eye sees only a complete picture.
STAGE 3 Divide your completed statements into two paragraphs. Give your text a suitable title.
THE UNIVERSITY OF DANANGCOLLEGE OF FOREIGN LANGUAGES
DEPARTMENT OF ENGLISH FOR SPECIFIC PURPOSES----- -----
NGUYÃÙN THË CÁØM TUÏ, M.Ed
ENGLISHIN
TELECOMMUNICATIONS
Danang 2008UNIT 1 NETWORKS Reading and Comprehension 1 Read the following description of national network. As you read, complete the labelling of Figures 1a, 1b, and 1c. The UK national network comprises:a) the local network: the lines between the subscriber and local exchangeb) the junction network: - the circuits between a local exchange and another local exchange
- the circuits between a local exchange and a primary centre, sometimes termed a tandem exchange- the circuits between a local exchange and a secondary centre, sometimes called a Group Switching Centre (GSC)
c) the main / trunk network: - the circuits between GSCs
- the circuits between GSCs and tertiary centres, known in the UK as District and Main Switching Centres (DSCs and MSCs)
In the local network, each subscriber is connected to a local exchange. To reduce the number of cables, the local network is usually divided into three parts:
a) the subscriber circuit: This consists of the telephone set, in the customer’s premises, and a cable pair, often an open-wire line, which is connected to a distribution point (DP)b) the secondary circuit: This is made up of a number of pairs (a multi-pair cable) connected over - or underground to a cabinet, sometimes called a cross connection point (CCP).c) the primary circuit: This is composed of a number of multi-pair cables (a multi-unit cable) connected in ducts or in a cable tunnel to the main distribution frame (MDF) in local exchange.
In the trunk network, all non-local calls are set up via a GSC and the main network. In the UK , 70% of all traffic is routed direct to another GSC, 24% via one other GSC. The traffic which can not be handled by these direct routings is carried by a new network, called the Transit Network. This network, which also carries overseas traffic to the International Gateway Exchanges, comprises 11 MSCs and 26DSCs, known collectively as Transit Switching Centres (TSCs). Transmission on this network can be coaxial cable or radio link. EXERCISE A Comprehension
Answer the following questions1. What do the following abbreviations stand for? a) GSC d) DP b) DSC e) CCP c) MSC f) TSC2. What is another term for? a) the main network d) a tertiary centre b) a primary centre e) a cabinet c) a secondary centre 3. What means of transmission are mentioned in the passage? Example an open wire line4. What types of traffic does the transit network carry? Reading and Comprehension 2Read the following passage about data networks. As you read, complete Figure 1d. Public data networks are designed for data transmission only. They therefore avoid the limitations of speed, etc. of transmission over the switch public telephone or telex network. The Nordic Public Data Networks is a circuit-switch type of digital network and its basic purpose is to provide a means of synchronous data transmission. The network consists of a number of components which are interconnected as shown in Fig. 1d. The data switching exchange (DSE) controls the set up and clear down of data calls, and monitors the connections and functions of the network. This exchange, which is capable of handling 100 calls per second, may be supplemented at a later date with a special service centre (SSC) for the introduction of certain new facilities. The DSE is connected to a data circuit concentrator (DCC). The purpose of the concentrator is to collect traffic from a number of individual subscriber circuits. This traffic is passed via time division multiplexed high speed link (TDM) to the exchange. These TDMs, which consists of time division multiplexed streams (64
Kbps), also transfer traffic between the DCC and one of the multiplexors (RMX). The multiplexors (RMX and DMX) connect several subscriber lines either directly to the DSE or to the DCC which passes traffic to the DSE. Between the RMX and the DMX and the data terminal equipment (DTE), the data circuit terminating equipment (DCE) is located in the subscriber’s premises. It primarily provides the standardized interface between the DTE and the network. Lastly, the DTE, which consists of a printing or alphanumeric visual display terminal or a computer, provides the subscriber with the data reception facilities. EXERCISE B ComprehensionAnswer the following questions
1. Match the components with their appropriate functions. (Note: Some components have more than one function)
Components Functions1. DCC2. RMX / DMX3. DSE4. DCE5. SSC6. TDM7. DTE
a. introduction of new facilitiesb. provision of data reception facilitiesc. collection of traffic from subscriber circuitsd. connection of subscriber linese. transfer of trafficf. control of set up and clear downg. provision of interface between DTE and networkh. monitoring of network connections and functions
3. What is the advantage of data networks compared with data transmission over the telephone?4. What is the capability of the DSE?5. What does the data terminal equipment consist of?
EXERCISE C ActivityBelow are some of the facilities a subscriber in the Nordic Public Data Network can have. Match them with the appropriate description.
Facilities Descriptions1. Abbreviated address call2. Direct call3. Closed user group4. Outgoing calls barred5. Group number6. Connect when free7. Charge advice
a. On dialling, the subscriber is always connected to a pre-determined number.b. The same number is used for several equivalent terminals. The connection is made to a free terminal.c. A number of subscribers are protected against calls from subscribers outside the group.d. The subscriber cannot call other subscribers.e. The subscriber uses only 2-digit numbers for a limited number of other subscribers.f. The subscriber is informed of the cost of a call on completion of a call.g. A call to an engaged connection is put in a queue and established when it becomes free.
Language Study 1
CLASSIFICATION Look at the expressions of classification in the following sentences:
The network is composed of / consists of / comprises / is made up of three parts The local network can be / is divided into three parts can be / is broken down into can be / is separated into
AB+There are two exchanges. Both are traditional electromechanical exchanges. AB . Two SPC exchanges are installed, one to extend the central area, the other to serve the new area.BBBB
A+70% of traffic is routed direct from one GSC to another GSC
EXERCISE D Use the map to complete the sentences below
1. The Newtown telephone network ...................... four......................, two secondary centers and a......................_
2. The Area ...................... into 3 sub-areas: North ......................3. There ...................... secondary centres. ...................... are connected to the DSC in Sisley by ......................4. There ...................... junction routes between the secondary centres: ...................... direct and ...................... via a local exchange.5. Routing from ....................... local exchange to ........................ can be direct or via ................... exchanges.6. ...................... Northern and Southern areas are served by .................... local exchanges.
WORD LIST - Unit 1READING 11. (N) An underground pipe in which cables may be laid.2. (N) An underground hole for carrying cables.
3. (N) (also called concentric transmission line) A cable in which one conductor is centred inside and insulated from a metal tube that serves as the second conductor.The inner conductor is solid or stranded copper wire. Flexible metal braid acts as a return path. The cable is protected by an insulating jacket.4. (N) The transmission of signals through space by electromagnetic waves - usually applied to the transmission of sound and code signals.* (N) A band of frequencies of a width sufficient to permit its use for radio communication.
The width of a channel depends on the type of transmission and the tolerance for the frequency of emission.
5. (N) Messages transmitted or received along a communication channel READING 2
1. (ADJ) (also called circuit-connected) When a circuit is connected, it is used for / occupied by the entire duration of the call.2. (N) A switching system that lets a large number of telephone or data processing subscribers use a lesser number of transmission lines or a narrower bandwidth, such as by storing messages until lines become available and then selecting messages for transmission on a first-come or other priority basis. It collects traffic from subscriber circuits.3. (V) To switch signals, in telecommunications, in a timed sequence so that many different receptors share a single wire or bus to conserve wiring. * (N) A process of transmitting more than one signal over a single wire or cable. There are two types: parallel and serial processing. Parallel processing frequency shares the bandwidth of a channel. Serial processing time shares multiple signals. In serial processing, signal speed is so fast that it is possible to multiplex four different coded signals through single decoder driver and have them appear on four different displays without a flicker.
* (N) A circuit combining two or more input signals into a single output signal for later recovery of the input signals. It can be performed with multiple analog CMOS IC switches and the use of digital decoding that allow one of many inputs to be passed to the output.4. (N) The transmission of two or more signals over a common path by using a different time interval for each signal.5. (N) The condition in which two or more varying quantities have the same speed or reach their peaks at the same instant of time. * (ADJ) In step or in phase, as applied to two or more circuits, devices, or machines.
UNIT 2 TRANSMISSION Reading and Comprehension 1Read the following article about optical fibers. As you read, label Figures 2a, 2b, and 2c. Fiber optic communications, in which electrical signals are converted into pulses of light that are squirted along very thin glass pipes, have several advantages over conventional copper cables:
- The signal fades (attenuates) less so repeaters can be more widely spaced.- Fibers can carry a lot of information.
- Most fibers are made from silica, which is very cheap. At present a kilometer costs £1,000 or more but when they are produced in bulk, this figure should come down to as little as £25.- Fibers are immune to interference and crosstalk.- The material is lightweight and flexible. A 500m fiber weighs about 25kg; a coaxial cable of the same length weighs 5 tons.
Although ordinary glass can only support effective light transmission for a few tens of meters, optical fibers, which are made of pure glass, can carry light signals for up to 50 km without amplification. Silica glass fiber has two components - the highly transparent “core” at the centre and the opaque surrounding called “cladding”. Three main types of fiber are possible: stepped-index monomode, stepped-index multimode and graded-index multimode (see figures below). Stepped-index fibers proceed from transparency to opaqueness in straight, defined bands while graded-index fibers go progressively from transparency to opaqueness. Monomode fiber has a very narrow core - such a fiber can support just one “guided electromagnetic mode”. In a multimode fiber, up to 500 light rays, each of slightly different wavelengths, pass through. Telecommunications engineers want to keep reflections in the core to a minimum so that pulses of light do not overlap and make messages unintelligible. In the early days of fibers, engineers used graded-index multimode fiber, rather than stepped-index, to keep overlapping to a minimum. But it is more satisfactory to use monopod fiber, in which pulse spreading does not occur. Light sources can be either light-emitting diodes (LEDs) or lasers. The former give less powerful signals but are considerably cheaper and last longer. The latter, however, produce light of closely-defined wavelength and so are suitable for monomode fibres.
There are two types of photodetectors - the silicon pin photodiode and the silicon avalanche photodiode. The avalanche devices are generally more sensitive but they are also more expensive. EXERCISE A Complete the following tables
Glass fibre
Compositions Types Main features Quality(a)(b)
Stepped-index multimode
Overlapping *
(c) (d) (e)(f) (g) (h)
Light sourcesTypes Features Applications
(i) (j) Multimode and monomode(k) (l) (m)
PhotodetectorsTypes Features
EXERCISE B ActivityMatch each of the advantages of optical fibres with an appropriate explanationAdvantages
1. Potentially low material cost2. High immunity to interference and crosstalk3. Very large information bandwidth4. Small and light cable5. Complete electrical isolation
Explanations
a. This means that they are suitable for crossing places which contain lots of electrical apparatus that give off stray signals. A fibre optic link is also difficult to “tap”.
b. This means that the signal fades less so that repeaters can be more widely spaced.c. This means that fibres can carry a lot of information, 8,000 or more telephone
conversationsd. This means that when manufacturers start to produce fibre in large quantities, the price
will be relatively low.e. This means that the cables can easily be laid and that they will not occupy much duct
space. Reading and Comprehension 2Read the following passage about electronic exchanges. Most of the world’s telephone traffic is still handled by exchanges of electromechanical design, each with thousands of wear-prone exposed moving parts. Analogue exchanges of this type are costly to install and maintain, and are subject to familiar faults such as crossed lines, noise and wrong numbers. Many of the world’s telecommunications administrations have explored other, digital, solutions. They are designing networks that offer: a much higher quality of service than before, using the latest microchip technology with few or no moving parts; less interference than previously; lower installation and maintenance costs; and much faster connection speed for calls and fewer wrong numbers than in the past.
The main characteristics of a digital exchange are:1. Integrated Digital Transmission and Switching
Speech and other signals are digitally encoded and a common method of time division multiplexing is used in both transmission and switching equipment. The main advantage of this system is that the transmission loss encountered by speech becomes more or less independent of both distance and the number of exchanges through which a call is routed.
2. Stored Program Control (SPC) is the application of data processing and computer techniques to an exchange, thus providing a powerful, flexible method of controlling the operation of the exchange.
3. Common Channel Signalling (CCS) uses just one (go and return) pair of signalling channels, not directly associated with the traffic circuits, for performing all the signalling functions of an entire route which may contain several hundred traffic circuits.
4. Microelectronics technology is the application of solid-state semiconductor technology to provide components which range in function from a single active element (e.g. transistor) to large scale integrated circuits. Use of this technology offers small physical size and reliability, together with automated design, manufacture and testing. The components are fixed onto printed circuit boards, and if there is a fault, the defective printed circuit board can be taken out and replaced by another in a matter of seconds.
EXERCISE C Complete the table
Classification Electromechanical exchange Digital exchangeTransmission type Analogue transmission Digital transmission and switching
Installation a. ................................... b. ...................................Maintenance High maintenance cost
c. ...................................Low maintenance costd. ...................................
Technical comments
Crossed linese. ...................................Rigidity of design Wrong numbersf. ...................................
g. ...................................h. ...................................i. ...................................j. ...................................Much higher evolutionary potentiala. ...................................
EXERCISE D Match each of the headings with one set of functions
1. Integrated Digital Transmission and Switching2. Stored Program Control3. Common Channel Signalling4. Microelectronics technology
A. The application of solid-state semiconductor technology to provide greater reliability, smaller size and automated design.B. The application of data programming and techniques to an exchange, thus providing a greater control and flexibility in the operative of the exchange.C. The use of one pair of channels not directly associated with the traffic circuits, to perform all signalling functions on a complete route.D. Speech and other signals are digitally encoded and a common method of time-division multiplexing is used.
Writing
STAGE 1 Use Figure 2d to order the sentences below to form a text describing a simple FDM system.
A. The second and the third channels cannot be transmitted directly over the line.B. At the receiving end, filters separate the three channels and finally demodulators restore
channels 2 and 3 to their original frequency position.C. To illustrate the principle of a frequency division multiplex (FDM) system, consider the
simple case of transmission of 3 telephone channels.D. Now, the three channels can be passed over the common line, boosted at intervals as
necessary.E. First, they are passed through a modulator which frequency shifts them to frequency
bands 4 300 - 7 400 Hz and 8 300 - 11 400 Hz respectively.F. The first of these channels can be transmitted directly over the common line and occupies
the bandwidth 300 - 3 400 Hz.
STAGE 2 Use the above description of an FDM system as a model to write a description of a TDM system, using Figure 2e as a basis
WORD LIST - Unit 2READING 1
1. (N) The technique of transmitting light through long, thin, flexible fibres of glass, plastic, or other materials. Bundles of parallel fibres can transmit complete images.2. (V) To be reduced in strength or energy 3. (N) The presence of unwanted signals4. (N) The unwanted transfer of energy from one circuit to anotherThe sound is heard in a receiver along with a desired program because of cross modulation or other undesired coupling to another communication channel.
5. (V) To partly cover something by extending over its edges6. (N) Dispersion and therefore fading of strength of pulse
7. (N) An amplifier and associated equipment that processes weak signals and retransmits stronger signals without reshaping their waveforms. It can be one-way or two-way.It is used in telephone lines, undersea cable, and fibre optic cables to overcome the effect of signal attenuation in the transmission media.8. (N) The region in which light can pass through9. (N) The region in which light can not pass through10. (N) Silicon dioxide11. (N) The ratio of the velocity of a wave in a vacuum to that in a specified medium12. (N) Differing successively in expansion characteristics13. (ADJ) Having a single sudden change in amplitude and a period of time at the new amplitude value14. (N) A semiconductor PN junction diode which converts electrical energy into light15. (N) A semiconductor PN junction diode which is sensitive to light, causing a reverse current to flow when light shines on it; or in another to say, the reverse current varies with illumination.16. (N) (Abbreviated to APD) A photodiode operated in the avalanche breakdown region to achieve internal photocurrent multiplication, thereby providing rapid light-controlled switching operation. It can have infra-red responnse, as required for detection of modulated light from lasers or LEDs.It absorbs photons in the P-type region near its PN junction and generates electrons that traverse the lighter doped P-type 17. (N) (Abbreviation for Positive-Intrinsic-Negative) A semiconductor structure that has a high-resistance intrinsic region between low-resistance P and N- type regions. Microwave diodes, photodiodes, switching diodes, and voltage dependent variable resistors are made with this structure.18. (N) A detector that responds to radiant energy; i.e. energy transmitted in the form of electromagnetic radiation, such as radio waves, heat waves, and light waves.It is also called a light detector, light sensitive cells, light sensitive detector, or photosensor.
READING 2
19. (N) The actual power that is lost in transmitting a signal from one point to another through a medium or along a line20. (N) A control system using a digital computer that can translate or otherwise alter an input program by using internally storeed instructions and ten executing the rewritten program.21. (N) The technology of constructing and using electronic circuits and devices in extremely small packages through the use of integrated circuits or other special manufacturing techniques.It is also called micro-miniaturization.
WRITING
22. (N) A multiplex system for transmitting two or more signals over a common path by using a different frequency band for each signal23. (V) To change the frequency of a radio transmitter and oscilator24. (N) A filter that transmits alternating currents below a given cut-off frequency and substantially attenuates all other currents.(N) A filter that allows only the band of frequencies to pass without attenuation. Frequency above and below the passband are rejected.(N) A frequency band in which the attenuation of a filter is essentially zero.25. (N) (Abbreviated to PAM) Amplitude modulation of a pulse carrier26. (N) (Abbreviated to PCM) Modulation in which the peak-to-peak amplitude range of the signal to be transmitted is divided into a number of standard values, each value having its own three-place code. Each sample of the signal is then transmitted as the code for the nearest standard amplitude. 27. (N) A decoder that extracts useful information from a pulse-coded signal28. (N) A device which accepts distorted pulses and produces well-formed pulses
CONTENTS
Page
Unit 1 4 5678
SECTION 1 ELECTRONICSIntroduction to ConductivityReading and ComprehensionWord study Describing shapes
Word formation 1- SuffixesLanguage study 1. Describing position and connection 2. Relative clauses 3. Pronoun links between sentences Information transfer Mathematical symbolsGuided Writing Describing a diagramSummarizing Superconductivity
Unit 2 Semiconductor diodes
Reading and ComprehensionWord study Word formation 1- PrefixesLanguage study 1. Writing instruction - Describing an experiment - Reporting an experiment 2. Describing graphs 3. Time clausesInformation transfer Transistor characteristicsGuided Writing Writing explanationsSummarizing Modulation
Unit 3 Alarm systemsReading and Comprehension 1Reading and Comprehension 2Word study Compound nouns Language study 1. If-sentences - Unless 2. Reduced time clausesInformation transfer Understanding diagrams Writing Linking facts and ideas
Unit 4
High definition television
Reading and ComprehensionWord study Circuit symbols Language study 1. Expressing the Certainty 2. Reason and result connectivesInformation transfer Logic gatesWriting Making paragraphs
Unit 1Unit 2
SECTION 2 TELECOMMUNICATIONSNetworks
Transmission
