The Electric Eye: Jack of All Trades
I
ONLY a few years ago the American people got their first close-up of a curious little instrument called the ‘electric eye.’ To the nontechnical person, it was simply a device that would open doors automatically. Few people outside of physical laboratories knew what made it work; they could only observe what happened when it was installed at the entrance of a building.
They saw two metal posts about five feet apart, each with a small round window the size of a baseball. Between these windows streamed a horizontal beam of light — an intangible barrier about three feet from the ground. When your body severed this light beam, the door swung silently open, and waited as though held by an unseen attendant. After you passed through, the door slowly closed, with due regard for your coattails.
Wherever the light beam was installed, people gathered to watch it work. Film stars were photographed using the automatic doors leading to the trains in New York’s Pennsylvania Station, and for months the small fry spent their spare time strutting in and out. It was a fascinating toy.
What people observed was one of the simplest of the many tasks which the versatile device has been taught to perform. The beam of light, which came from an ordinary light bulb, fell upon a photoelectric cell, the vital part of the mechanism. This sensitive cell, which looks like a small light bulb, translated the interruptions of the beam into electrical energy, and a small motor was started which opened the door. Since the turn of the century, physicists had been familiar with the functions of the photoelectric cell, but it had been little more than a laboratory marvel. Now it was harnessed and set to work.
Geared to a multitude of uses, it has brought about one of the most important technological developments of the century. The phototube, as the eye is often called, gave the movies their voice. It sends news photographs over the telephone wires. Upon it rests all progress in television. It has been taught to simulate seeing, hearing, talking, feeling, and even smelling. It steers ships, catches burglars, sorts fruit, sniffs smoke, nabs speeders, counts pills, and matches colors. It does all these things with a swiftness and an infallibility that make men seem clumsy oafs. It has gone into the big factories. It works all day inspecting finished goods, rejects faulty products, and gives an unfailingly accurate report when the whistle blows. It will measure a diameter of a machine part within a hundred-thousandth of an inch, and, as the most reliable device for the measurement of light, it is invaluable to astronomers and physicists.
In the few short years since the photoelectric cell was put to work, its influence has extended to the tallest building and the smallest village. It has worked an irrevocable change in the lives of 130,000,000 people, and its career of usefulness has only begun.
II
Once the first practical electric eye was developed, laboratory men and manufacturers were quick to perceive the many uses to which it could be adapted. Here was a gadget which enabled a beam of light to move a mechanism in a split second, which would take delicate variations of light and transform them faithfully and instantaneously into corresponding variations of energy, and which was infinitely faster and more accurate in performing its set tasks than the human eye, not to mention the hand.
Rigging up the electric eye to open a door was a simple matter for engineers, but they soon found that with a little ingenuity the eye could be utilized to solve far more complicated traffic problems. It was installed in elevator floors to ensure precise ‘leveling off’ at landings. Light from a small bulb set in the edge of each floor fell upon the phototube, whose current actuated the braking mechanism at the correct moment. Another eye kept the elevator door from closing on last-second entrants, and injuries and damage suits were cut down.
Put the eye in front of the vehicle door of a public garage, where pedestrians sometimes break the light beam accidentally, and the door will open for automobiles but not for people. For this job there are two beams several feet apart, and both must be intercepted or the eye will not respond. If a car emerges from the garage and breaks the beams in the reverse direction, the eye doesn’t open the door again behind it — it knows the difference.
One city garage had an antiquated, single-lane ramp which was used for both entering and leaving. The margin of profit was so low that, rather than remodel the place, they might as well nail up the doors. They called in the electric eye. Now, when a customer drives up, the door opens and a red light flashes on automatically if a car is coming out. The outbound driver is warned in the same way, and, since the eye can easily make up its mind in a thousandth of a second, there is no chance of a disagreement about the right of way. There is a doctor in a Western city who got tired of opening and shutting his garage door during the grippe season. Now when he rushes to his car he turns a flashlight on the door, and it is open when he gets there. The eye, mounted in a little metal box on the door casing, responds when the light hits it. The door closes after the doctor has driven out, and on his return the rays of his headlights strike the eye and the door opens again.
The eye has been taught all manner of tricks in the measuring and regulation of traffic. Attach it to a recording machine and it will count people or vehicles. Put it in a gate and ask it to count cars going one way and forget the others, and it will obey orders. Eyes installed beside the road will count automobiles and record their speed. There are two beams across the road, and speed is computed by the time which elapses between the breaking of the first and of the second beam. Before spending millions for a new highway, it is advisable to get accurate data on local traffic conditions, and alert state highway departments from coast to coast have been quick to adopt the new tool. One of the most striking examples of the regulation of traffic is the elaborate system used on the Bay Bridge which carries commuters’ trains between San Francisco and Oakland. By means of 4000 electric relays, the eye sets track switches, signals reports of approaching trains, and operates controls which establish car speeds. It stands guard before vehicular tunnels with a beam of light as high as the tunnel’s roof. If a truck comes along with too high a load, the beam is intercepted, a warning bell rings, and complications are avoided.
Scores of traffic uses are being tested experimentally. There is the nightly battle of headlights, which blinds drivers and causes accidents. A practical photoelectric device has been patented which will automatically dim the lights of approaching cars. A our headlights act upon a phototube in the cowl of the oncoming automobile, and a mechanism turns on its dimmer; the other driver’s headlights do the same for you. After you pass, your lights resume their former brilliance.
For many commercial purposes a strong light source is used to give the eye its signal for action, but so delicate are its perceptions that it can be made to respond to even the faintest light. For instance, Chicago’s Century of Progress Exposition was opened by the feeble rays of the star Arcturus, which fell upon a photoelectric cell and caused it to turn on the Exposition’s lights. The eye can be ‘set’ to respond to any degree of daylight, and for this reason it has been installed in the last few years in many schools, factories, offices, and streets for the automatic control of artificial lighting.
A busy teacher may not notice that the sky is overcast and that children’s noses are boring into their arithmetic books. The vigilant eye, in its little metal box on the wall, turns on the schoolroom lights when daylight fails, and turns them off when they are no longer needed. This system has been installed in classrooms in East Cleveland, Ohio; Evanston, Illinois; Poughkeepsie, New York; and many other places. It is also used by airports, whose numerous landing lights must be turned on when daylight is inadequate. The device is far more critical of lighting conditions than the human eye, and never fails to put the lamp in the window when pilots need it.
When storms blot out the sun, millions of householders turn on their lights, and utility companies must be prepared for the added load. Here, too, the electric eye comes in handy. Mounted on the roof, it surveys the sky, and warns the plant engineers well in advance of the rush.
One of the eye’s most sensational rôles is that of policeman. For a new man on the force, it has nabbed quite a few burglars. For this purpose, the so-called ‘black’ or infra-red light is used. The human eye cannot see it, but the electric eye reacts to the invisible rays at either end of the spectrum. The black light from an inconspicuous source near the baseboard of a room may be reflected by a mirror on the opposite wall to a phototube still farther down the room. Or it can be even more complex: you can crisscross the room with the invisible rays so that no intruder, even if he crawls on his belly, can enter without breaking one of the beams and setting off the alarm. A further refinement is a concealed camera with a flash bulb and a noise-making device. The burglar hears the noise and looks at the camera just in time to be snapped for identification. In the early days of the phototube, some electrical research men in a New Jersey factory were delighted to hear that the stockroom was being pillaged. They tried out the new gadget, with beautiful results. The eye has also been installed to watch over sleepwalkers and mental patients. A light beam is broken if the patient leaves his bed, and an alarm is sounded in the room of a nurse or member of the family.
A number of practical domestic uses have been considered. It would be convenient, for instance, if your porch light turned on automatically when someone approached your door at night. It would be pleasant for a housewife with dough on her hands to start the gas oven by breaking a light beam. In either case, the device would be simple to install, but the cost would be at least $100. Manufacturers are aware of these possibilities, but at present they can only speculate about future sales prices due to increased output of equipment. General-purpose phototubes now sell for about one quarter of their price ten years ago, but the tube is only one part of the mechanism. The only application likely to interest today’s householder is the burglar alarm. For other purposes the new device can be used more efficiently and economically in the transportation and utility fields, in large buildings and in manufacturing industries.
III
Only a few years ago the electric eye was unknown in American industry. The older engineers pinned their faith on mechanical automatic devices, many of which had served reliably for a long time. A new school of electronic engineers had to be trained to give the eye its chance. Then a revolution which has not yet reached its climax descended upon our factories. In assembly lines and continuous-process plants of every description the electric eye is inspecting products, preventing waste, and saving labor.
It is used in all the big steel mills and automobile plants, in textile and paper factories, in printing shops, food-packaging plants, and scores of other establishments. Everywhere it shows an amazing adaptability. It is reasonably predicted that in another ten years virtually everything that we eat, drink, smoke, read, wear, or ride in will be measured, weighed, sorted, cut, counted, or inspected by the tirelessly peering eye.
In many plants it is doing secret tasks that no one will describe. While big firms like General Electric, Western Electric, Westinghouse, the RCA Manufacturing Company, and the Electronic Control Corporation of Detroit are turning out tubes, application equipment, or both, to fill the great new demand, some of the huge industrial corporations are hiring their own electronic engineers and making their own equipment. When they find new uses which will reduce manufacturing costs, they keep still about it to preserve their advantage over competitors.
A glance at the eye’s known activities in industry is impressive enough. In sheet-steel plants, it measures the long, moving strip for cutting, rhythmically orders the big shears to do their work. When an automatic process machine is clogged by material, the eye stops the machine and prevents expensive breakages and loss of time. Installed in the maw of a giant stamping machine, the eye protects the operator. If his hand blocks the little pencil of light, the jaws are suspended agape until it is safely withdrawn.
No human being or mechanical contrivance can count as fast as the electric eye, and this proficiency has led to many new uses. Consider, for instance, a forty-inch width of finished cloth several miles long which is zipping along between rollers. Sometimes in the best regulated of plants one side starts creeping up on the other. If the ‘skew’ is not corrected immediately, ruined or inferior material results. Put a phototube over each edge of the cloth, with a light source beneath, and it will count the crosswise threads as they speed by, even if they go as fast as 10,000 threads a second. If the totals of the two counts begin to vary, the eye signals a mechanism which straightens the cloth instantly. Several mills have installed this device.
The fact that the eye will discriminate between color vibrations as well as between light and shade has made it invaluable to makers of paints, inks, and dyes. Mounted in a recording spectrometer, it will make a chart of any color sample, thus providing an easy means of standardization and comparison. In a simpler application, it will separate the brown eggs preferred by Bostonians from the white ones popular in New York, inspect oranges and throw out the green ones, or look at flour and determine its bran content. Brewers, makers of soft drinks, and oil refiners put the beam through a pipe where liquid is continuously flowing. A change in color, indicating a change in quality, is reported at once.
Installed in a factory chimney, the eye measures the density of the smoke and reports it to the engine room, where the information is useful in regulating the fuel supply. As a smoke detector in warehouses it prevents fire losses.
In any plant where there is a conveyor moving along with a line of objects, the eye is in its element. In the automobile factories, where it has been working for the last five years, it counts painted fenders as they move along an overhead track. The light doesn’t mar the finish, and it doesn’t make mistakes. When packaged goods move down the line, it counts the sheep and tosses out the goats. The beam can be adjusted to weed out damaged or imperfectly sealed cartons. Put the light beam over a scale bar where packages are filled automatically, and it will stop the flow of material when the proper weight is reached, thereby dispensing with a human inspector. And the eye is eliminating the ‘baker’s dozen’ method when small objects are sold in packages by number. Its count is sure, and no surplus margin is needed.
Introduced at a time when laborsaving devices are multiplying rapidly, the electric eye is one of the most impressive of the lot. A big warehouse which used to employ a large force of girls to sort beans by hand now depends entirely upon the eye, which never misses a speckled bean or a pebble, and doesn’t collect wages. It is stated that in counting and sorting operations alone the eye could replace several million workers, a possibility whose social and economic implications cannot be ignored.
IV
Engineers have only begun the task of utilizing the many talents of the electric eye, for its career in industry began less than a decade ago. It did not even exist as a practical commercial device until 1924. At that time Bell Telephone Laboratories asked Dr. Herbert Eugene Ives, their director of electroöptical research, to work out a method by which photographs could be sent over telephone wires. Dr. Ives believed that the photoelectric cell, long familiar to physicists, could be adapted to the purpose.
To go back to beginnings, the basic principle of the electric eye was discovered accidentally by young Heinrich Hertz in 1887. His discovery of the ‘photoelectric effect,’ a phrase which may be more simply stated as ‘the effect of light upon electricity,’ was only an incident of Hertz’s experiments with wireless waves. While working on his waves, Hertz noticed something odd, which anyone but a scientist might have disregarded as an irritating interruption. He was watching a device in which a piece of zinc and a piece of burning magnesium wire played a part. There were two electrically charged metallic conductors, separated by a short air gap, and Hertz was jumping electric sparks across the gap. What he observed was a tiny additional discharge of energy which all his experience told him had no business there. Edison had noticed much the same thing a few years before.
In searching for the cause of this small increase in the current that jumped across the gap, Hertz finally ruled out everything else but the invisible ultraviolet light which came from the burning magnesium wire. He concluded that the light had knocked the little stream of energy out of the zinc. It doesn’t matter that Hertz used zinc, or that the light was ultra-violet. What he stumbled upon was the fact that when light falls upon metals it makes them spit out electrons.
Hertz had never heard of an electron; no one had. Before anyone could find out what really happened that day in his laboratory, the old conception of the atom — that it was the final indivisible unit of matter, like a marble, so to speak — had to be demolished. It took daring physicists like Sir J. J. Thomson to demonstrate that the atom was a kind of little solar system; that it has an electrically positive nucleus in the middle, and that around this nucleus swims a school of negatively charged particles called electrons, fantastic midgets of matter no larger than a billionth of a pinpoint, which move at speeds as fast as 160,000 miles a second. Hertz’s light, falling on the piece of zinc, had upset the electrical balance of its atoms and had knocked a procession of electrons out of their orbits. They had to go somewhere, and, since they were negatively charged, they were attracted by the positive conductor. They leaped across the gap, closing the circuit, and set up the little stream of energy which he observed.
Soon after Hertz made his discovery, other men came along and built its principles into the photoelectric cell, which has not changed essentially through the years. Simply described, it is a glass bulb which looks like a light bulb, part of which is lined inside with potassium, a silver-colored material. A wire connects this lining with a battery, and another wire from the battery is connected with an upright terminal in the middle of the bulb. Thus we have a circle broken by the gap of air between the silver-colored lining and the central post, or electrode. The potassium is very sensitive to light. Put this bulb in a dark room and nothing happens. The negatively charged electrons in the atoms of potassium swim contentedly in their orbits. But if you turn a flashlight on the bulb, the electrons leave home in droves. Lured by the positive terminal in the middle, they jump madly across the gap, completing the circuit. If you connect a meter to one of the wires outside the bulb, it will show you that a tiny current is flowing. The stronger your light, the stronger the current will be. Cup your hand over the light, and the current will stop instantly. Flash the light in some sort of code, and the meter shows you that the current is copying it.
Scientists had penetrated the dark wilderness of the atom and returned with this marvelous tool. But for thirty years they couldn’t put it to work. The current was too weak. Its strength was only about one ten-billionth of what it takes to run an ordinary household bulb.
The problem of Dr. Ives and his coworkers at the Bell Laboratories was to find a method by which this anæmic current could be multiplied a few million times until it was strong enough to perform a useful function. They found their answer in another electronic device which derived from Hertz’s pioneer work — the vacuum tube. Early in the century, Lee De Forest had developed this tube so that it would amplify an electric current. Now a wedding was negotiated between the photoelectric cell and the amplifying vacuum tube. It is customary to think of developments of such importance as the reward of many years’ effort, but Dr. Ives and his associates, R. D. Parker, J. W. Horton and A. B. Clark, had the job finished exactly three months after the company asked them to look into the matter. The result was the first commercial application of the photoelectric cell.
Thus converted into a practical device, the eye took its first public bow in June 1924, when news photographs taken at the Republican Convention at Cleveland were sent over the wire to New York. The picture to be transmitted was wrapped around a cylinder, which revolved in a light-proof metal case. A carriage bearing the eye and a thin pencil of light slowly traveled the length of the cylinder, like the needle on an old-fashioned phonograph record. The light beam thus performed a long, tight spiral around the cylinder. The eye scanned the narrow, illuminated band of the photograph, and its sensitive electronic current varied in strength with the lights and shades of the picture. Bolstered by the amplifying tubes, this varying current went over the wire to the New York office. It could actually be heard by those present in the form of a hoarse, vibrating scream. In the receiving machine, the current hit a metal ribbon which concealed a light beam. The impact of the current made the ribbon shimmy from side to side, emitting a varying stream of light which copied faithfully the degrees of light and shade seen by the eye in Cleveland. The pencil of light fell upon a photographic film wrapped around a revolving cylinder, and thus built up, line by line, a reproduction of the original photograph.
The next morning the pictures were spread across the pages of the newspapers, and soon the word ‘telephoto’ entered the language. Now the Associated Press telephones pictures every day to more than a hundred newspapers.
Then the electric eye brought in the ‘sound track’ talking picture film, which supplanted the bulky and fragile records used in the first ‘talkies.’ By a device similar in principle to the telephoto, the eye opened up the wide field of television. Other uses followed rapidly, and its future is limited only by man’s imagination.
The young science of electronics is seething with new ideas, and the final effect of photoelectric devices upon the business of living is unpredictable. For instance, there is a hydroelectric substation in the Southwest over which the electric eye has complete charge. It is given a specially made graph which shows the varying load of electricity normally needed throughout the day. With not a human in sight, it methodically releases the amount of water needed from hour to hour. And a machine has been reported which will take a drawing, scan it photoelectrically, and translate its lines into the movements of cutting tools, ejecting the finished part. It is claimed that a number of machines will take orders simultaneously from the same master drawing.
Whether or not this device turns out to be practical, we can be sure that robots of similar significance are on the way. Led forth from the atomic cave of mysteries and harnessed to human affairs, the photoelectric cell will open doors now undreamed of.