"AN INTRODUCTION TO MINING ELECTRONICS" 1977 BRITISH COAL BOARD SEMICONDUCTOR TRAINING FILM GG28455

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[00:00:00][Music] Okay. Heat.

[00:00:24]Okay.

[00:00:33][Laughter] The mining industry today is using more and more electronic equipment.

[00:00:48]But what does this word electronic mean?

[00:00:54]Early in this century, the thermionic valve was invented.

[00:00:58]And electronics was the word chosen to mean the study of these valves.

[00:01:04]It was chosen because valves work by transmitting electrons internally.

[00:01:13]Then in the 1940s, semiconductors were discovered.

[00:01:17]A semiconductor is a material which conducts current under some conditions but not others.

[00:01:24]This is the material that transistors and diodes are made from.

[00:01:31]This is a semiconductor diode.

[00:01:34]This is a transistor.

[00:01:38]It doesn't look much like a valve and it works on a different principle but it can do the same job.

[00:01:45]Anything a valve can do can be done by some semiconductor device.

[00:01:53]So electronics today deals with both valves and semiconductors.

[00:01:58][Music] A valve is more complicated than a transistor or a diode. So it's more expensive to make.

[00:02:12]Transistors and diodes are smaller than valves. They use less power and they can operate at lower voltages.

[00:02:20]So nowadays they've almost entirely taken over the jobs that valves used to do.

[00:02:28]These jobs are of three sorts.

[00:02:31]Rectifying, amplifying, and switching.

[00:02:38]Rectifying is done by diodes and amplifying and switching are done by transistors.

[00:02:47]Rectifying means allowing a current to pass in only one direction.

[00:02:54]A one-way valve in a hydraulic line allows fluid to pass in only one direction.

[00:03:02]In the same way, a semiconductor diode allows electrons to pass in only one direction.

[00:03:09]This is the conventional symbol for one.

[00:03:14]The second job that semiconductor devices can do is to amplify.

[00:03:22]Amplifying means allowing the variations in a small electrical input to control the variations in a larger output.

[00:03:31][Music] Amplifying can be done by the transistor.

[00:03:42]A transistor generally has three sections. The base, the emitter and the collector.

[00:03:50]All three sections are made of semiconductor material. And the emitter and collector are separated only by the base which is extremely thin.

[00:04:01]This is the symbol for a transistor.

[00:04:05]Base, emitter, collector.

[00:04:13]If we try to pass current straight through a transistor from emitter to collector, we'll find that it has a very high resistance.

[00:04:21]So high in fact that it acts as an insulator, allowing no current to flow.

[00:04:28]But if we apply a voltage across the base and emitter, giving the junction between them a forward bias, the resistance across the whole transistor will fall, allowing current to flow through it from emitter to collector.

[00:04:44]The more base emitter voltage we apply, the lower the resistance across the transistor will fall until it's virtually zero and the current can flow freely through.

[00:04:58]The base emitter voltage controls the flow of current through the transistor.

[00:05:05]So if this control voltage pulsates, it will mold the current flowing through the transistor into the same pulsating form.

[00:05:14][Music] The larger current will be like the smaller current amplified.

[00:05:27][Music] The control voltage and the current it controls rise and fall together.

[00:05:35][Music] Third, semiconductors can be used as switches.

[00:05:47]When no voltage is applied in the control circuit, the transistor has a very high resistance and almost no current can flow through it.

[00:05:58]If sufficient voltage is applied in the control circuit, the transistor will have a very low resistance and current will flow through it freely.

[00:06:08]So if we put a switch in the control circuit, the opening and closing of the switch will control the flow of current through the whole transistor.

[00:06:17]A transistor can therefore be used to act rather like a single contact relay.

[00:06:25]A relay has one advantage over a transistor.

[00:06:29]Its control circuit and the circuit it controls are completely isolated from each other.

[00:06:39]With a transistor, the two circuits have to have a terminal in common.

[00:06:45]But this disadvantage is far outweighed by the transistors compactness and speed. Some transistors can operate millions of times a second.

[00:06:59]Rectifying, amplifying, switching.

[00:07:05]Components performing these three simple functions can be combined in circuits to do very complicated jobs.

[00:07:26]The circuits that control these machines are built up from semiconductors and other simple components such as resistors, capacitors, and inductors.

[00:07:36]These components can be combined in many different ways.

[00:07:43]Because each component can do only a simple job, circuits often need to use large numbers of them.

[00:07:51]This can make the plan of an electronic circuit look very complicated.

[00:07:57]But a circuit diagram is like a road map.

[00:08:01]Nobody looking at a map like this could hope to take it all in at a glance.

[00:08:07]But just as a road map is made up of simple components and can best be taken in a bit at a time, so an electronic circuit can best be taken in a bit at a time.

[00:08:21]The jobs done by electronic circuits fall into three categories. Collecting information, transmitting information, applying information.

[00:08:32]This information can be of many kinds.

[00:08:36]It can be the temperature of a bearing or the position of a machine on a coal face or a water level or even the spoken word.

[00:08:49]Hello. Is Jimmy there? Jimmy Johnson.

[00:08:54]Hi.

[00:08:55]>> But before a circuit can handle any sort of information, the information must be transformed into an electrical signal.

[00:09:03]>> Hello, Jimmy. Look, that gate them box on fives is still not working properly.

[00:09:10]That's it.

[00:09:10]>> Any piece of equipment that can do this is called a transducer.

[00:09:14]>> Same as it was before. In a telephone, the microphone is the transducer.

[00:09:22]This type of microphone contains a metal diaphragm and behind the diaphragm is a drum packed with granules of carbon and sealed at each end with a carbon disc.

[00:09:37]The carbon granules form an electrical resistance between the discs. If the drum is compressed, the granules pack more closely together and the resistance between the discs falls.

[00:09:52]When pressure is taken off, the granules loosen and the resistance rises again.

[00:10:00]When a sound enters the microphone, it makes the diaphragm vibrate and the resistance across the drum varies in time with the sound waves.

[00:10:10]Well, we're still on it at the moment, but it's making a terrible clatter. Eh, >> so when a direct current is passed through the drum, >> variations in the current form an electrical reproduction of the sound.

[00:10:22]>> All right, then we'll change over onto the spare.

[00:10:26]>> These small changes in current can be amplified by transistors to a level where they're strong enough to drive a loudspeaker or receiver.

[00:10:34]>> Yes. Yes, that's all right. Another transducer is the strain gauge.

[00:10:42]If it's placed under tension, these wires will stretch very slightly and their resistance will increase.

[00:10:50]Fitted into a load cell like this, a strain gauge can be used to measure the tension on a hage chain or conveyor or to weigh coal.

[00:11:06]In this test rig, the tension shown on this scale is being applied to the load cell and the reading from the load cell is being amplified by transistors and displayed electronically.

[00:11:35]Another transducer changing information into electrical current is the float switch.

[00:11:44]When water reaches a float, the float tilts and a tilt switch inside it closes a circuit.

[00:11:54]So it collects the information that the water has reached the level of the float.

[00:12:00]This is a different type of information from the varying information we get from the strain gauge. Either the water has reached the float or it hasn't. So the switch is either on or off. Either there's an electrical signal in the circuit or there isn't.

[00:12:18]This onoff information is known as digital information. It's called digital because it's related to the system of binary digits.

[00:12:28]In the binary code, every number can be expressed as a string of ones and zeros.

[00:12:36]So if current on is used to represent a one and current off is used to represent a zero, we can express any number in the form of electrical pulses.

[00:12:53]This is why we convert numbers into ones and zeros to begin with.

[00:13:00]that the electrical signal we get from the string gauge or a telephone is not simply on or off.

[00:13:07]And you'll send one of your lads over to have a look at it.

[00:13:11]Oh, that's fine. Fine.

[00:13:14]Yes. Yes, that's all right.

[00:13:16]>> This varying type of signal is known as an analog signal.

[00:13:21]>> The current is an analogy of the information it's carrying.

[00:13:24]>> Fine.

[00:13:26]Analog systems are a form of measuring.

[00:13:32]Digital systems are a form of counting.

[00:13:38]And it's possible to express the same information in either form.

[00:13:43]This is an analog measurement. The needle moves in proportion to the current.

[00:13:50]This is a digital measurement. A count of the number of milliamps.

[00:13:58]One advantage of using a digital signal is that it's less affected by distortion.

[00:14:05]Poor transmission will leave a pulse recognizable as a pulse under conditions where an analog system would be useless.

[00:14:17]>> Command post >> target enemy battery range 11,500.

[00:14:24]Hello. Hello.

[00:14:27]>> Target enemy victory. Range your 11,500.

[00:14:32]>> Hello. I can't hear you properly. This is bloody line.

[00:14:37]Hang on.

[00:14:43][Music] [Music] It's for similar reasons that photographic information from distant planets is sent back to Earth in digital form.

[00:15:10]Another advantage of digital information is that it can be handled very efficiently by semiconductor switching devices.

[00:15:19]One of the most common of these is the bistable.

[00:15:22]This uses two transistors with the base of each one connected to the collector of the other.

[00:15:32]So whichever transistor is switched on, it will hold the other switched off and the one that is off will hold the other on.

[00:15:47]Connected to the base of each transistor is an input which can be used to switch on its transistor.

[00:15:55]If we apply a negative pulse at input A, T1 will switch on and T2 off.

[00:16:03]The bstable will stay in that state until a negative pulse is applied at input B. Then T2 will switch on and T1 off. The device is called a bstable because it will always stabilize in one of these two states.

[00:16:22]If the last pulse it received was at A, it will be in this state.

[00:16:28]If the last pulse was at B, it will be in this state.

[00:16:34]So the bstable acts as a memory. It remembers whether A or B received the last pulse.

[00:16:43]Using binary terms, when T1 is on, we can say that the bstable is in the one state and when T1 is off, the zero state.

[00:16:57]As a bstable contains two transistor switches, one of which is always on and one off, we can use it to switch current along one path or another.

[00:17:09]If the bstable was in the zero state and a pulse of current was fed into it, the pulse would emerge along one output line.

[00:17:18]If the bstable was in the one state and a pulse of current was fed into it, the pulse would emerge along the other output line.

[00:17:27]It would be possible to connect these two leads to the inputs of a second bystable in such a way that a pulse fed through the system would change the state of the second bystable to match the state of the first.

[00:17:46]In this way we can pass a bit of information from one by table to another.

[00:17:55]But suppose we wanted to transmit this voltage reading 1195 m expressed in binary terms. This is 101011 molts 11 digits.

[00:18:14]These could be stored in a bank of bstable memory cells.

[00:18:21]If we had another bank of memory cells somewhere else and the two banks were connected, we could feed a pulse through the first bank and transmit the complete number to the second bank.

[00:18:34]But to transmit even one number in this way would need far too many connections and our cables would have to have hundreds of cores. What we need is some way of transmitting the information one cell at a time. If we can send the digits one after the other, we can send as many as we like over a cable with very few cores.

[00:18:57]There are several systems in use that will do this. One is Dino Link.

[00:19:04]In this system, information collected in the colly is gathered at out stations.

[00:19:18]Each art station has a bank of memory cells where the information is stored.

[00:19:24]The central station in the control room has a bank which contains one cell for every cell in every outstation.

[00:19:34]Connected to every cell is a duplicate cell. And these duplicate cells are connected into a ring of cable.

[00:19:43]Information enters the memory cells of the outsts using one core of the ring of cable. A pulse called the transfer pulse can be fed to all the memory cells at once.

[00:19:58]The information in these cells has now been duplicated into the corresponding cells in the ring.

[00:20:05]Another core of the cable carries a shift pulse to all the cells in the ring.

[00:20:11]This pulse makes every cell pass its information on to the next cell along, even if that cell is at the next station.

[00:20:19]They all do this at once. So all the information in the ring moves round one step.

[00:20:26]And every time a shift pulse is applied, they move around another step, bringing the information to the central station.

[00:20:43]Starting again, information enters the outst.

[00:20:51]A transfer pulse duplicates this information into the cells in the ring.

[00:20:58]Shift pulses begin, shifting the information around the ring, one step at a time.

[00:21:06]When the information has traveled halfway around the ring and is opposite the cells in the central station, the shift pulses stop and another transfer pulse is applied.

[00:21:18]This has duplicated the information in the ring into the central stores memory.

[00:21:23]At the same time, it has duplicated the information at the out stations into the ring once more.

[00:21:33]Then the shift pulses start again.

[00:21:38]And every time the information has traveled halfway around the ring, we get a transfer pulse.

[00:21:52][Music] The whole process is very quick so that information from the outsts is brought into the central station. hundreds of times a second. This means that any new information entering the outsts is passed on to the central station almost at once.

[00:22:23]Systems of this sort all share the advantage of transmitting information quickly and economically.

[00:22:31]Once the information has been transmitted, it can be displayed to an operator so that he can take decisions and a similar system will transmit his instructions back to the outst.

[00:22:46]Systems can also be designed to control machines automatically.

[00:22:58]Modern mining uses large amounts of information.

[00:23:02]With fast and accurate information, a collery can be run more safely and more efficiently.

[00:23:09]And handling information is what electronics is all about.

[00:23:18][Laughter] [Music] [Laughter]