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HIGH-SCHOOL CHEMISTRY
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An Electronic Primer C . T . PEARCE Westinghouse Electric and Manufacturing Company, Philadelphia, Pennsylvania
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LECTRONICS might be defined as the science of the chamber. This theory can be used to explain the electron in space. It is distinguished from the results obtained in a t least the majority of electronic other branches of electrical engineering in that it deals tubes. It also permits an accurate prediction of with the handling of electrons "in the raw" as it were; performance. that is, where they flow across an evacuated or gasFrom this, i t follows that practically all electronic filled space in a tube, rather than through a copper devices have the following things in common. wire. 1. They utilize a highly evacuated chamber. However, this Electronics is not a new science, although the general space may be filled to a low pressure with an inert gas or public has not been made very well aware of i t until vapor. 2. They have a negative terminal, known as a cathode, for recently. Many of the fundamentals of electronics the source of electrons. This cathode may he a plate, have been known for several years, but the first general coated with a special material, and relying upon either heat application was in radio. Electronic devices are now or light for its emission properties. It may also be a pool found in practically all fields of industry, and there has of mercury. been a very sharp increase in their usage during recent 3. They have a positive terminal, known as an anode, to collect the electrons. Care is exercised to reduce the years. In some instances, they have permitted the electron availability of the anode. development of entirely new applications, hitherto 4. They frequently utilize one or more additional control unknown because no equipment was available to give elements, usually referred to as "grids." between the the desired results. In others, they have replaced cathode and the anode. 5. As long as one main terminal is maintained as a cathode, or supplemented the existing forms of equipment, beand the other as an anode, these devices are inherently cause they do the job better. rectifying. This explains their wide usage in converting The present conception of matter is that each elefrom alternating to direct current. ment is made up of infinitesimally small bodies known Most of the advantages of electronic devices come as atoms. The atom, in turn, is composed of a number about because they handle the smallest indivisible of still smaller particles. Some of these particles have a negative electrical charge, while a corresponding particle of energy, the electron. This largely exnumber have a positive charge; thus keeping the sys- plains their flexibility and adaptability and their ease tem in electrical balance. The negative particles are of close and accurate control. This principle may be called electram, and are assumed to rotate about the crudely illustrated by considering a large pile of positively charged particles in the nucleus, just as the bricks. As long as they exist as a pile of bricks, they earth and planets revolve around the sun. The can be readily transported and many different uses various elements differ in the number of electrons and can be made of them. As soon as they are fabricated in the arrangements of their orbits around the nucleus. into buildings, however, they must be transported as This obviously does not cover all of the ramifications very much larger units, and their flexibility of usage is of the atomic theory, but is sufficiently complete for our very greatly curtailed. Some of the technical advantages peculiar to elecpurpose. An electric current is therefore represented by a tronic devices are as follows: 1. They can detect infinitesimally small amounts of power flow of electrons. One ampere of current requires a flow of over 6,000,000,000,000,000 electroks per and then amplify them into usable or measurable quantities. Regardless of the ratio of amplification, faithful second, so i t is seen that we are dealing with very large reproduction is obtained. numbers of very small particles. 2. They give practically instantaneous response and perfect It has been found that if all air is removed from a sensitivitv. - . as cornoared to the time lae and sensitivitv tolerance always present in mechanical devices. chamber, electrons flow rather freely across this space 3. They are inherently rectifying. when subjected to a voltage. This flow is greatly 4. They permit control of the application of power in periods increased if the electronemitting material is heated. of fractions of a second, without the use of an arc-interCertain types of materials will also give off electrons rupting device. This is true whether handling a fraction of an ampere or thousands of amperes. if light is thrown on them. This flow of electrons is 5. They can be used to transform light energy into electrical increased many times if the is filled to a low energy, as illustrated by the well-known photo tube. pressure with types of gases. The flow of 6. They have no moving or rotating parts. This makes for electrons can be very readily and accurately controlled less wear ss well as easier foundation and mounting prabby the usc of the proper control elements placed inside lems. 72
7. They can be used to generate waves of energy at any desired frequency. This characteristic is used in producing high frequency waves for x-rays, internal heating, germ killing, etc.
I t should be pointed out that the great majority of electronic devices are actually electronic only in part. The growth in the use of electronic tubes has been made possible only by the development of the necessary associated apparatus and circuits. The same will undoubtedly be true of future applications of electronic equipment.- The circuit apparatus necessary to apply electronic tubes requires from 4 to 200 times the value of the tubes themselves. Following are a few of the more important present uses of electronic devices. The familiar radio receiving set, already mentioned, depends on electronic tubes to amplify the very weak signals received over the air, so that they can be heard in the loud speaker. Electronic tubes are also used a t the broadcasting station to transform and amplify sound into radio waves. Television relies upon electronic tubes a t both the sending and receiving ends, to handle vision as well as sound. Carrier current relaying has been in use by electrical utilities for a number of years. It uses the highvoltage transmission line for the purpose of handling high-frequency signals, as well as its normal duty of carrying low-frequency power current. Its use serves to improve transmission line performance by the reduction in relay operating time. Electronic tubes are used to place the high-frequency signals on the line a t one end and remove them a t the other. The same principle can be used for communication and longdistance metering. The photo-tube or electric eye is a very important member of the family of electronic devices. It responds to light, and may be made sensitive to any desired color. I t can therefore be used for colormatching purposes. Photo-tubes may also be made sensitive to wave lengths outside the visible spectrum, that is, infrared, or ultraviolet. This makes them suitable for use in burglar alarms. The photo-tube has opened up a veritable host of applications for counting, scanning, or for control of any operation which can be accomplished by interrupting or reflecting a beam of light. Some of its uses in addition to those already mentioned are the counting of objects or persons, detection of defects in fast-moving objects, tension control, door opening, automatic elevator leveling, temperature control, and thousands of others. It is probably the most popular of any type of electronic tube for industrial use. In the broad field of control, electronic devices are already used very widely. In this category are supersensitive voltage and speed regulators, precise speed control of electric motors over a very wide range, and the control of operations from such variables as temperature, speed, time, and light. Resistance welding of certain types of material
would not be possible without the use of a powersize electronic device known as the "ignitron." I t feeds thousands of amperes into the weld but for periods of one-hundredth of a second or less. I t is only by applying tremendous heat very momentarily that several of the modem alloys can be satisfactorily welded. This has been a great boon to industries engaged in the fabrication of materials. The "ignitron" is also utilized for the conversion of alternating current todirect current in large quantities. It therefore finds application in the chemical industry, where a great amount of direct current power is required for electrolytic purposes. Reference is made in particular to the production of aluminum and magnesium. The "ignitron" is also used widely in the transportation industry for supplying large blocks of direct current power. An air-cleaning device known as the precipitron was made available a few years ago. I t charges small particles electrostatically, and then attracts them to a charged plate of the opposite polarity. High-voltage electronic rectifying tubes are required for charging the particles as well as collecting them. This device has a cleaning efficiency of 90 per cent as compared to 25 per cent for the best mechanical filter. I t is particularly effective in removing very small particles. For example, it will absolutely eliminate tobacco smoke and hay fever pollen. It is finding an increasingly wide usage in all types of applications where absolutely clean air is a requisite. It has just recently been installed in some machine shops to remove oil vapor suspended in the air. The x-ray tube generates waves of a very high frequency, which penetrate solid matter. It has been used for several years in the medical field, but has recently been found to be oi great industrial value in detecting internal flaws in material. By discovering such defective material before machine work has been performed on it, many valuable man-hours of work are saved. The present scarcity of tin has forced the tin plate
manufacturers to apply the tin electrolytically instead of dipping i t in a hot bath as before. This reduces the consumption of tin to about one-third of the previous amount required to cover the same surface. Unfortunately, the electrolytic process gives a dull, rough surface. It has been found that a bright surface can then be obtained by melting the thin coating of tin with the heating of high-frequency waves. For heating a strip 30 inches wide traveling a t 1000 feet per minute, 1200 kw. of power, a t about one-half radio broadcasting frequency, is required. This is equivalent to the power of 24 of the largest broadcasting stations. Installations totaling approximately three times the power of all our regular broadcasting stations together are now in operation. Higb-frequency tubes can be used to produce internal heat in an object, and are therefore able to dry .out material from the inside out, rather than the ont:side in. The use of internal heat instead of external .gives great savings in time in the drying of thick sections of organic materials, curing of plywood and plastic materials, etc. The cathode ray oscillograph records the path of a beam of electrons. Its chief virtne is that a stream of .electrons has no inertia, and therefore follows exactly the actuating forces.
The electron microscope gives magnifications not possible with the optical type. Electronic amplifying tubes are used in a very sensitive balancing machine. Vibration impulses, down to 25 millionths of an inch, are magnified to a point where they can be located and corrected. Many types of electronic devices have proved vety valuable in the medical field. Prominent among these is the x-ray tube, which has already been mentioned. Another is the "Sterilamp" which generates waves in the ultraviolet range and destroys many bacteria and spores. The installation of this type of lamp in operating rooms has been found greatly to reduce infections. Stii another medical application of electronic tubes is that of generating high-frequency heat in the human body. This is of great therapeutic value. There are many secret types of electronic devices giving essential aid in the prosecution of the war. The details on most of these applications will probably not be available to industry until after the war. These wartime uses have given considerable impetus to the development of electronic devices, and have served to uncover many new uses for them. From this it follows that their peacetime uses will be many in the postwar world.
