Carl & Jerry: The Electronic Bloodhound
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An Internet search for a perchlorethylene (PCE) detector made by Honeywell in the 1960s turned up nothing other than a reference to this John T. Frye Carl & Jerry article in Popular Electronics magazine. PCE is a toxic substance which was formerly (and possibly still is) used in the clothes dry cleaning business and as a degreaser. The substance is central to this "The Electric Bloodhound" technodrama™ in the September 1964 issue of PE magazine. In his typical style, Mr. Frye uses these stories as a teaching medium while entertaining with the exploits of a couple teenaged electronics junkies who by now are in college studying electrical engineering. This time, Jerry is in the lab admiring a new type of detector that monitors the concentration of certain particulates in the air, and sound an alarm if it exceeds a defined level. By an incredible coincidence, while explaining its operational principle to Carl, that device proves to be useful in collaring a thief who had just robbed a pedestrian. A long list of other Carl & Jerry adventures is at the bottom of the page. Carl & Jerry: The Electronic Bloodhound
By John T. Frye W9EGV Carl and J The fall semester was well under way at Parvoo University. It was a beautiful autumn day, and while Jerry was straightening out an assignment with one of his professors, Carl rode around the campus looking at the new eight-story residence halls and the new ten-story graduate house. As an engineer, he was especially intrigued by the novel way more than ten thousand new seats had been added to the capacity of the football stadium. The floor of the stadium had been excavated to a depth of ten feet, thus making room for thirteen rows of new seats along both sides and one end. Jerry was not in the room they shared in Residence Hall H3 when Carl returned, but Carl knew where to look for his friend. Sure enough, Jerry was in the Electronics Laboratory examining a new piece of equipment that had come in for study and evaluation. The device resting on the bench in front of him consisted of two units. One was a case with a couple of jeweled indicator lights and a meter reading 0-100 ppm on the front of it. Attached to this by a long, flexible, multiwire cable was a strange-looking object from which Jerry had removed a protective metal cover with ventilated ends. Two small vertical chassis were mounted about a foot apart on a metal base plate, and a metal rod and a sealed glass tube about an inch in diameter reached across from one chassis to the other. A small glass tube was mounted on the outside of the left-hand chassis behind a round hole, and some sort of lamp bulb was mounted directly opposite behind a similar hole in the right-hand chassis. A combination reflector and protective shield was around this lamp, and directly beneath the shield were two small electric motors. One looked like a phono motor with a ventilating fan on its shaft; the other had the appearance of a timer motor. "What the heck's that?" Carl asked, pulling a stool up to the bench. "Can't you read ?" Jerry teased, pointing to the neatly lettered PER-TECTOR legend on the front of the instrument. "So what's a 'Per-Tector'? What does it 'pertect' against?" "It's a gadget brought out by the Apparatus Controls Division of the Honeywell Company in Minneapolis to detect the presence of perchlorethylene, a toxic gas used in dry cleaning. It'll be installed in coin-operated dry-cleaning plants and will automatically turn on extra exhaust fans whenever the gas concentration at this detector unit - which can be mounted away from the amplifier and control unit - reaches 40 ppm, well below the danger point for human beings." "O.K. How?" "This little tube behind the hole in the left-hand chassis is a sensitive ultraviolet radiation detector. Opposite it behind the matching hole in the right-hand chassis is a special ultraviolet lamp focused on the detector tube. The output of the detector is amplified and used in a kind of bridge circuit so that when the full and unobstructed radiation from the lamp falls on the detector the circuit is balanced and the meter reads zero. "But this little fan is constantly drawing in air from the room and pushing it through the space between the lamp and the detector. Since perchlorethylene gas molecules have the ability to absorb ultraviolet radiation, if any of this gas is present in the air the instrument is 'sniffing,' even as little as one ppm, the presence of the gas will cut down on the radiation reaching the detector and produce a reading on the meter. This instrument is adjusted so that when the gas concentration reaches 40 ppm a relay turns on the ventilating fans. It could be adjusted, though, so that this would happen when the concentration was as low as 10 ppm." "What's the purpose of that long glass tube and the other stuff?" "It's part of a really clever idea. Over a period of time, dust, dirt, and oily particles may collect on the lamp and sensor tube. To compensate for the loss of ultraviolet energy transfer this produces, the gadget automatically recalibrates itself. That long glass tube is filled with a specified concentration of perchlorethylene. Once every twenty-four hours, this little motor turns the steel shaft and rotates the gas-filled tube into place between the ultraviolet source and the detector and switches on calibrating circuits inside the amplifier. "The balancing circuits adjust automatically for the proper reading for that concentration of the gas. After calibration, a latching mechanism that has been holding the tube in place releases and this counterweight pulls the tube out of the path of the ultraviolet beam. If the dirt accumulation is so heavy that proper compensation is impossible, this warning light on the amplifier comes on and tells the operator to clean the lamp and sensor." "Don't other substances besides perchlorethylene absorb ultraviolet radiation?" "Sure. The device can detect fumes from gasoline, paint, lacquer, ammonia, styrene, foam rubber, tear gas, acids, ripe bananas or apples, liquor, and even vodka! It can't tell the difference between these various odors the way the human nose can, but it can react quantitatively to any of them; and, up to a point, it can be made especially sensitive to a particular substance. For some reason, one fact that determines which gas the device will be most sensitive to is the distance between the detector and the source of radiation. Honeywell is experimenting along this line at the present time. The possibilities are limitless." "Let's see it do something," Carl requested, intrigued in spite of himself. "O.K. I'll put the cover back on the detector unit so air drawn in by the fan will pass between the detector and the lamp. Notice that this electric bell takes the place of the exhaust fans the unit would normally control. See? Nothing happens when the unit is turned on and inhales only room air, but watch as I uncork this little bottle of perchlorethylene down here at the end of the bench." Only seconds after the bottle of cleaning fluid was opened, the meter pointer started to climb. As it went past the "40 ppm." mark, the bell started ringing and continued to ring while the meter pointer went over against the peg even though Jerry had corked the bottle again. Then, slowly, the pointer came back down, and around mid-scale the bell ceased to ring. In the comparative quiet that followed, the boys heard loud voices outside the laboratory. When they went to a window, they saw a police squad car headed into the curb with its rotating top light still flashing. Two uniformed officers stood on the sidewalk holding the arms of a squirming little man so that he faced a well-dressed civilian getting out of the squad car. The boys rushed outside to see what was going on. "Is this the man who robbed you, Mr. Garland?" one of the officers asked the well-dressed man. "Bugsy here has quite a record with us." "Yeah, you dumb cops are always leaning on me," the squirming little man said, his weazened face distorted with hate. "What's the beef this time?" "I-I can't be certain," Mr. Garland said, staring intently at the bat-eared hard -eyed man in dirty shirt and tattered trousers. "He had a handkerchief over his face, and all I could seem to see was that long, sharp, switchblade knife in his hand. I've always had a kind of thing about knives, and I could almost feel it making shish kebab of my liver." "Let's see if he has a knife, Mac," one of the officers suggested. In spite of Bugsy's loud and profane protest, they turned his trouser pockets inside out. From the left pocket came a couple of crumpled dollar bills. The right pocket yielded a total of eighty dollars in neatly folded fives and tens. That was all. There was no knife. "He could easily have gotten rid of it, Dolan," Mac said. "Mr. Garland, do you know how much money he took?" "It happens I do," Mr. Garland answered. "While home for lunch I spilled some coffee on my trousers, and I changed into a suit the cleaner had just delivered. When I emptied my pockets I noticed I had exactly eighty dollars in bills. These were not in a wallet. I have a bad habit of carrying bills folded together and shoved down into my pocket. "I drove downtown, parked the car in a parking lot, and took a shortcut through an alley toward my office. That's where the man stepped out from behind some packing cases with the knife in his hand and demanded my money. I gave it to him. He ran on into the alley, and I ran toward the street and hailed your squad car. This fellow looks very much like the one in the alley, but I can't be sure. I don't want to make a mistake." "Bugsy," Officer Dolan demanded, "where did you get all that money?" "Won it in a crap game!" the unkempt man snarled, "all eighty-two dollars of it. Why don't you two give up? Unless this character had his bills marked, you're out of luck. You heard him say he couldn't identify me. I don't have a knife. I'm carrying more money than he said he lost. If I'm rousted again by you dumb flatfeet, you're going to be up before the judge on false arrest charges." Jerry suddenly plucked Officer Dolan's sleeve and whispered to him at some length. The policeman, with a puzzled look on his face, finally turned to his fellow officer and said, "Mac, this guy thinks maybe he has a way of telling if that money is Mr. Garland's or not. I don't understand how, but it's worth a try. Bugsy, come along with us into the laboratory and absorb some college atmosphere - you can use it." As they reached the door of the laboratory, Jerry took Mr. Garland by the arm and stopped him. "Stay here by the door if you don't mind," he said. "You'll soon see why." He switched on the Per-Tector and turned to the policemen who were still keeping Bugsy between them. "This is the machine that might tell us if any or all of the bills came from Mr. Garland's pocket," he said. "It's very sensitive to cleaning fluid such as may have been used in cleaning Mr. Garland's suit. Since that suit is fresh from the cleaner, I'm hoping anything carried in the pockets will have picked up enough of the cleaning fluid fumes to register on the meter. We'll soon know. First, let's try this handkerchief of mine which has not been exposed to cleaning fluid." He placed the handkerchief directly in front of the air intake of the Per-Tector, but the meter pointer never budged. "Now, Mr. Garland, let's have your handkerchief," he said. "I'll come get it. I don't want the machine to 'smell' your freshly cleaned suit." Mr. Garland took a handkerchief from a hip pocket, and Jerry picked it up with a pair of plastic tongs and laid it in front of the sensor unit. Instantly the meter pointer moved clear to the right, and the electric bell began to ring. "Looks like we're in business," Jerry said triumphantly, returning the handkerchief. "Now I wish one of you officers would place the bills from Bugsy's pockets, one at a time, in front of the air intake of the machine and watch what happens to the meter pointer. After each reading, remove the bill and let the pointer go back to zero before trying another." Officer Dolan did exactly as Jerry suggested, and the results were dramatic and damning. Each of the five and ten dollar bills caused the meter to peg and the bell to ring, but when the one dollar bills were offered to it one at a time, the meter pointer did not budge. "We -I -I -I, Bugsy?" Officer Dolan said. "O.K., O.K.! So I heisted the character. But you're not going to pin no armed robbery rap on me. That 'long, sharp, switchblade knife' he was yapping about was nothing but a rubber imitation they sell for kids to play with. You'll find it in a trash can back in that alley." As he finished speaking, he suddenly lunged toward the bench holding the Per-Tector and tried to raise his foot high enough to kick the sensor unit, but the alert officers grabbed him in time. As they led him toward the door, he turned his head for a last malevolent look at the boys and the electronic bloodhound that had been his undoing. "You lousy, stinking finks!" he snarled at them. As if in answer, there was a whirring of the motor and the glass tube moved into position for automatic recalibration. "The poor devil didn't even have the last word," Carl said softly as they heard the calibration tube rotate out of the ultraviolet beam.
Posted January 12, 2024
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Carl & Jerry, by John T. Frye