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THE first question generally asked is "What is industrial electronics as distinct from all the other kinds of electronics we know, and what does it include?" The first part of this question is the more difficult to answer, for it requires that we draw a line somewhere between one branch of electronics and all the others.
Any such distinction may be invalid the day-after-tomorrow.
Therefore we shall answer that one generally by saying that any electronic devices which comprise a regular part of industrial processes will be considered industrial electronics. It will thus include all those applications in which electronics is the major ingredient in the process, as well as those in which electronic devices serve only to help control a process by measurement and feedback -type controls, or where electronics is involved only in recording data about the process.
In this way we have automatically started answering the second part of the question, namely, "What is included?" We know that some processes in industry depend on electronics as an essential, functional part of the program. This we find in such applications as dielectric heating (heat applied to insulating materials), induction heating (heat applied to conducting materials) and microwave cooking (Fig. 101) which is related to both, but mostly to the former. We can also consider in this category any processes using electrolysis to separate constituents of a solution, plating done by purely electronic means without the conventional plating "bath" and, as another extreme, a printing process called xerography in which the letters are deposited on the paper electronically by charged particles on a surface.
Fig. 101. Modern "radar" oven cooks foods in unbelievably short
time. (Raytheon Corp.)
In the other categories we can include all the various means of control, from controls directing the operations of a large oil refinery to the simple photoelectric safety control on a punch-press, which protects the operator from accidental exposure of his hands in the machine when its crushing force shapes a metal part. Other applications include such items as electronically-controlled printing presses, elevators, toothpaste -filling machines, postage stamp printing machines and the leveling controls for a huge steam shovel.
In the measurement class we find many processes guided in accordance with precise data obtained electronically through temperature, pressure, position, density, speed, weight and humidity controls. We find, in this category, equipment to detect pinholes in enormous sheets of steel, or very tiny particles of metal in boxes of baby cereal; counters which count every bean sealed into a package of colorfully -printed cellophane; automatic testers which accept or reject vacuum tubes, capacitors or resistors according to predetermined tolerances; radiation detectors which automatically warn of danger when the radioactivity level in a process becomes unsafe, and, on the other hand, gages for registering the level of liquid in tanks which use radioactivity as their active element. Those are but a few examples of the endless variety of electronic measuring and control devices used in modern industry.
Another category would include instruments which are used purely for measurement, such as the electronic recorders which keep a precise count of the gallons of oil in a refinery or quarts of milk processed in dairy machines, the sensitive bridges which keep track of the flour in storage bins tall as a skyscraper, and the gages that tell the exact temperature of tiny furnaces used in transistor manufacturing. This field makes use of sensitive transducers which translate mechanical forces and physical quantities into electrical signals, which are, in turn, transformed by means of various kinds of recorders, gages and indicators into continuous records of the processes under observation for the purpose of maintaining production control and to facilitate troubleshooting in case of production difficulties.
Finally, there is a large group of electronics equipment used in industry for communication of all kinds. These are often used together with equipment in the other categories. For example, we may mention such applications as industrial closed circuit TV systems, which permit one man in an operating position to keep careful watch, simultaneously, over many gages widely separated in a plant; telemetering systems which convey data over consider able distances for control, coordination and recording purposes; and the familiar industrial public address and music systems, special intercoms and portable, pocket sized communicators for large warehouses. Other examples in the communications category include alarm systems of all types and proportions, and for all kinds of purposes, from keeping out intruders to warning of fire, flooding, overheating and the presence of dangerous gases.
Industrial electronics viewed in all its facets is truly an enormous spectacle that staggers the imagination. All this equipment operates silently, swiftly and accurately and, for all the customer can tell, forever without the slightest hitch and hesitation. But this is reckoning without the thousands of service and maintenance people who are always alert to possible failures and breakdown of this equipment which, despite the emphasis by design engineers on maximum reliability, cannot be made completely 100% dependable without becoming economically impractical. For this reason the manufacturers of industrial electronic equipment usually provide excellent service facilities to their customers because of their realization that a single breakdown might cost the customer millions of dollars in lost production. As part of this program they help to train customer maintenance men in the servicing of each separate device as it is installed in the plant. As a result, we have many service personnel who are experts on one particular make of one specific class of instruments, and a large group of technicians who are thoroughly familiar with a substantial variety of electronic devices used in their particular plant, but few who can approach any electronic device in industry with confidence,, knowing that whatever the gadget is, they can fix it.
It is obviously impossible to take up all aspects of industrial electronics servicing in a single book. However, by pointing out the similarities between these devices and those with which you are already familiar from radio, hi-fi and television work and study, we intend to show you that the basic circuits involved in these devices are the same, and that we simply have many new combinations of circuit blocks already familiar to the reader but now used for different purposes. This is the goal we hope to achieve in this guide.
A bit of history Because we are getting more and more accustomed to new electronic devices in our daily environment, which a decade or so ago were simply laboratory oddities, we assume that this influx of electronics is something new, something of today and not yesterday, and something even more of tomorrow. What we do not realize is that electronics, in one form or another, has played a major role in some of our industries for many decades -a role of great importance, and without which we would not have some of the many products we now take completely for granted.
In the late 1880's Nicola Tesla invented a process for electrolytic-ally separating iron from its ore. Call this the beginning, if you wish. But long before that, in the early part of the 19th century researchers were aware that metals could be heated with induced electric currents, the principle of induction heating. It was in the early 1900's, however, that the first practical induction furnaces were produced by Northrup, which used high frequencies for melting metals. But it was not until almost 25 years later that induction heating was applied in practice to a variety of metal processes requiring intense heat. In other words, this kind of industrial electronics has been with us for several decades.
Dielectric heating was even slower in getting started. Although the heating effects of electric fields in capacitors of radio transmitters had been noticed almost from the beginning of radio broadcasting in the early part of the 20th century, practical applications of dielectric heating did not appear until the mid-30's, when the idea was first applied to the process of drying tobacco leaves. Today, dielectric heating is utilized in a wide range of industrial processes.
Electronic control also is not entirely new. In 1890, the same Tesla who invented the three-phase induction motor and generator, which are the backbone of industrial power, demonstrated the use of electronics for the remote control of a model boat. The idea was so far advanced for the times that few besides Tesla could understand the possible applications of such devices.
Today, as a direct result of the development of reliable devices, tubes and components, electronic controls are used in all phases of industry, as well as in military, commercial and domestic fields.
Electronic measurement, using the term as distinct from electrical measuring methods, is also a relatively recent technique, although ideas in this field were developed and applied soon after the vacuum triode was introduced. The development of oscillators made possible a number of measurements which had been impossible before. Who would ever think, for example, of measuring the inductance of several inches of straight wire without the use of very-high-frequency measuring devices? On the other hand, such a measurement is only of importance at these very high frequencies. The introduction of electronic measuring devices closely followed the needs of the communications industry, but, once developed, they were readily adapted for other purposes.
The introduction of the cathode-ray tube by Johnson and van der Bijl in 1922 gave impetus to the development and use of numerous electronic measuring devices. Now, as we look at the technician's array of tools and equipment, the cathode-ray oscilloscope is one of the most important testing and measuring devices is his arsenal, along with the electronic vacuum -tube voltmeter, wattmeter, frequency meter and the various generators to create the signals needed for many measurements.
What about the future? That depends on what you call the future. If you are thinking in terms of electronic controls in industry, of machines operating without the benefit of human hand or judgment, the future is here and now. Already, many products in our complex economy are made entirely by automatic machines which also count, inspect, pack and, after shipment, often dispense the product automatically. With some imagination we can foresee the electronic control of many additional production processes. For example, we now have fully automated equipment for the automatic assembly of printed circuit boards, circuit modules and micro-modules, produced entirely by machine. Furthermore, completely automatic wiring machines have been invented which are so versatile that, upon instruction from a computer, they can wire a series of different devices accurately and precisely without human intervention. Although there will be a gap between what we can do with electronics in industry and what is being done, you can be certain that the future application of electronics to many processes will require the skills of a great number of qualified and experienced electronic technicians for the installation, maintenance and servicing of this equipment.
What is being done now? Perhaps the simplest way to get an idea of the possibilities in the field of industrial electronics today is to take a look at what kinds of industrial electronic devices are being used and where they can be found. This will be a limited sampling only, and the list will be confined to the more generally applied equipment.
First let us look at dielectric-heating generators which are generally used where considerable heat evenly distributed throughout the material is needed in the processing of dielectric materials. The principles involved in dielectric heating will be discussed in Section 3.
We shall briefly mention only a few examples of the application of dielectric heating to industrial processes. Dielectric generators are used extensively in wood gluing processes in the plywood industry and in cabinet and furniture factories. In this case, their principal purpose is to promote rapid drying of the glue, thereby cutting down the drying time from days to minutes. They are also utilized in the plastics industry for heating the plastic material as well as the forming mold.
Fig. 102. Large dielectric generator being used for the baking of foundry
cores. (The Girdler Company.)
Better known as the Radarange, manufactured by Raytheon Corp.
Dielectric generators are used in bag -sealing machines to seal plastic food and merchandise bags. Similar sealing machines are used for the manufacture of plastic toys and such items as golf halls. Dielectric generators are used in the food industry to dry (dehydrate) foods, and in this process they have the advantage of not discoloring foods as conventional ovens do. Precooked foods are prepared in dielectric fields and so are hot dogs in automatic vending machines. Rubber product factories use the generators to heat rubber for molding and to vulcanize raw rubber. Plastic seat covers are "sewed" by dielectric heat, and plastic and wood wall panels are glued together in similar machines. Foundries use dielectric fields to dry and bake cores for forms, and pottery factories bake clay products in a fraction of the time required for conventional ovens. Green lumber for cabinet factories is kiln-dried by dielectric generators, and in one of the largest types of installations, large sheets of plywood are laminated (Fig. 102).
A final example of dielectric heating is the "radar" cooking range which derives its name from the fact that it operates at microwave frequencies. Microwave cooking has found many applications in food -processing industries as well as in restaurants where it can achieve in a few seconds what would normally take many minutes by conventional cooking methods.
Let us next discuss the industrial application of induction generators. Induction heat is used in the metal industries in various forms. In some of the larger installations it is used to melt and alloy various metals. Parts are heated in induction coils for hardening and sometimes for brazing. Large ingots and forgings are preheated with induction generators (Fig. 103) because the process is much faster and more thorough than conventional heating.
Annealing (removing temper) and soft soldering are two more applications of induction heating. It is also used in heating glass for the manufacture of vacuum tubes. This is possible because glass, when preheated to about 600° F becomes a conductor, even though it is an insulator at room temperatures. For this reason, induction heating can be used to heat both the glass and the elements in a vacuum tube. Extreme heating of vacuum-tube elements without heating the glass can also be done with induction generators, and this is used in the de-gasing process in vacuum-tube manufacture. Zone melting of semiconductor material is done in the field of an induction -generator coil. Sometimes parts which are to be shrunk together are quickly heated in such a coil and then assembled, for induction heat can be adjusted, as you will see, to heat just the surface of a piece of metal or to heat the entire piece evenly.
Another form of electronic heat is produced in electronic welding machines, which are commonly encountered in sheet metal products factories and in the vacuum-tube industry where small thin metal parts must be spot-welded together. Another common use of electronics is for the control of both conventional and special arc -welding machines. High-frequency arc welding can also be found in sheet -metal factories, and is particularly applicable where local heat is required without substantial heating of the rest of the metal.
It may be appropriate to point out here that metals can be welded without heat by ultrasonic welding machines that shake the surface molecules of the metals so they intermingle. Of course these machines are powered by electronic generators. Ultrasonic generators are also used in cleaning and washing, homogenizing, sterilizing and purifying, chemical mixing, and in such tools as ultrasonic grinders, drills and soldering irons. Ultrasonics is also used in flaw detection and gaging systems. Instruments of this kind are found in steel mills and metal fabricating plants, auto motive plants and diesel engine factories. All of these comprise a special class of electronic equipment which will be discussed in some detail later on.
Other classes of industrial electronic equipment can be found in just about any kind of industry. Photoelectric controls are used for detecting motion or the presence of an object where it should not be. Other photoelectric devices are used for gaging the thickness of wire, for example, or the density of smoke in a stack, or flaws in painted surfaces which reflect differently from other areas, and for such applications as sorting objects by color.
Photoelectric cells can be used to indicate liquid level or the density of a solution by passing a light through the liquid or a portion of it. They are also used for "reading" instructions punched in tape or cards which are employed to control large machine tools from a programming device.
Fig. 103. Large induction generator being adjusted by technician. (General
Electric Co.)
Photoelectric control, which converts information in light beams to electrical signals, is one way of controlling processes electronically. There are many other such controls - temperature controls using thermistors and thermocouples; controls where stress or strain is translated into electrical signals by strain gages; pressure controls; level controls; vacuum controls; speed controls and a host of others. Counting itself can be a means of control.
A preset counter, after a preset count has been reached, can perform a control function and then promptly reset and start counting again. Weight can be a control factor as can size, thickness, motion and speed, density, viscosity, and all sorts of electrical values such as resistance, voltage, conductivity, current, frequency, etc.
Controls do not always require some kind of transducer for converting the original measured quantity to a suitable control signal to operate automatic equipment. Some large machine tools for example, can be controlled by what is called a "program." The machine goes through a predetermined sequence of operations to produce its product. This "program" can be provided to the machine in a variety of ways. It can be fed into the servo control system from magnetic tape, punched paper tape, a magnetic or mechanical memory drum (a mechanical memory drum is like the drum in a music box, with switch contacts instead of tines) or even punched cards as used in business machines. This then becomes truly automation for these machines may produce the same part over and over, or a collection of different parts depending on the instructions provided for the operation.
If the operation is repetitive, timing is usually one of the most important control factors and can be performed electronically in many ways. The controls and program devices can simply be a series of timing controls, rather than a complex set of instructions.
A simple example of such a system is the home automatic washer, which goes through its single predetermined sequence, regulated by timing controls. Timing always plays a role in electronic controls, even if it is a minor one at times.
Recording is a large item in industrial electronics, and very many times the recorder is the controlling device also, recording and controlling on the basis of the same electrical value at the input. Sometimes the recorder is primarily a control device and the recording function is secondary and provided to make a record of deviations from a norm which occurred and which were corrected by the device. This then gives the operators of the process an opportunity to regulate other values in the system so that the least amount of correction is required, and the process operates more uniformly over longer periods of time.
In many cases a process takes place so rapidly and the product is produced in such vast quantities that the only way to keep track of what is produced is by some means of automatic recording, often with just a counter having printed readout. A readout is an electronic counter with a printer attached, which several times per second will print the sum of what has been produced or the amount produced in that fraction of a second. In this way, counters with printed readout can also be considered recorders and, as we go further in the direction of automation, more and more recording will be done in this "digital" manner, since the automatic plant functions best on a digital system.
Fig. 104. Industrial recorder of the single -channel type. This unit supplies
a record of power consumption. (Westinghouse Electric Corp.)
In the Section on electronic counters we will briefly discuss the basis of the most popular digital system in such control, the binary system, and how it can be converted to and from the more common decimal system. The binary system is not only important in control but also in digital computers, which are based on it.
Recorders keep track of all kinds of quantities, but they can register only electrical values and changes in them. Therefore the transducer is ever present with the recorder, unless strictly electrical values are to be dealt with in the system. Typical units in industry record such values as temperature, gas pressure, liquid level, steam pressure, weight, salinity or conductivity (Fig. 104).
But remember that a great number of these do not necessarily re quire electronics. Thus such items as pressure of any kind, vacuum and temperature may also be recorded by mechanical means. Even multiple records can be made mechanically, and very ingenious bellows and pen-arm arrangements have been designed which can keep track of as many as six items on a single chart. However, this is not common, for when many values are involved we will ordinarily use a multi -track electronic recorder which can keep track of 12 values simultaneously. Actually, the records are not exactly simultaneous. The recorder samples each value to be re corded periodically and prints an appropriate and distinct mark for each record once a second or more often if required.
Industrial communications systems are familiar in principle at least, to most who will read this volume. Thus you may find intercom and paging systems in all manner of factories, ware houses and plants. In fact, it is safe to say it is a rare plant which does not have some form of internal communications system. And some of these systems will set up special requirements for maintenance and adjustment, as dictated by the conditions in the plant.
Closed-circuit TV is a part of industrial electronics, and we will have something to say about the servicing of such systems.
Too often the subject of industrial electronics service is shrouded in mystery, as if it were some branch of electronics requiring special skills, special secret knowledge, very special equipment and maybe even special kinds of service technicians.
You will realize, when you have finished reading this guide, that, mostly, the service consists of calm evaluation of the function of the circuits, what their similarities are to circuits in other kinds of electronics, and how their malfunctioning can be detected and corrected. Special knowledge is involved only insofar as the particular instrument is concerned, and even there many of them are alike. And the calibration of industrial equipment, although perhaps sometimes very critical work, should not present serious difficulties to someone familiar with painstaking adjustment of TV receivers and accustomed to wrestling with "mechanical monsters" such as record changers and tape recorders.