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VOLUME -22 NUMBER 12
Publication Date: 12/1/2007
Front Page News
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Electronic Mfg. Services
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Special Feature: Test and Measurement
Product Preview: Electronics West / MDM
December 2007 Issue
Special Feature: Test and Measurement
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One-Man Continuity Tester: Born from Necessity
New CT20 continuity tester.
By Art Sesnovich, Extech Instruments, Waltham, MA
Continuity testers are simple devices, with the basic model often consisting of a multimeter and an assistant standing at the ready with jumper wires at the other end of whatever needs testing — sometimes with a walkie-talkie. Trying to do this job without an assistant and with conventional hardware has traditionally been perplexing. This admittedly low-tech operation was usually below the radar for new instrument developers.
But this was not the case for Joseph Blanchard, a self-employed electrical contractor, and former Bose technician, who is the mastermind behind the CT20 Continuity Tester Pro from Extech Instruments. While Extech holds the patent for this revolutionary product, which features the unique capability for single-person operation of wire and cable continuity checking and identification — the original concept, as well as numerous early revisions — was the result of Blanchard's efforts. And the concept arose primarily to serve his own need for a continuity tester that overcame the deficiencies of the testing products on the market at the time.
In 1987, Blanchard had just returned to his job as a residential electrician after a number of years at Bose, where he served as plant electrician and later as an audio lab technician. That tech job helped fulfill a passion for electronics that had been with him since his early childhood and, combined with his electrical experience, had given him a well-rounded industrial background. While Blanchard enjoyed the residential work, he did have one pet peeve — the lack of a suitable device for continuity testing. There were already a number of devices available, but they all had serious shortcomings. While some were intrinsic to each device, there was one issue that united them all: ringing out a line (as continuity testing was referred to 20 years ago) is extremely exasperating to do on your own.
"I tried everything available on the market," Blanchard said. "But with all of them, you ultimately put a continuity device on the end of a wire pair, then located what you thought was the other end, connected the wires together, and went back to your initial spot to see if the light was on, only to have to go back and take the wires apart. "If you were working on your own, like I was, this got to be pretty tedious."
"Because I was doing a lot of work on older houses, rather than new construction, there always seemed to be a need to figure out wiring patterns. Residents would see wires sticking out of their walls and didn't know if they were speaker wire, or telephone wire, or alarm system wire, or something else, and had no idea where they were supposed to go."
Each type of continuity testing device had its own unique problems. Multimeters, which had long been used for continuity testing, were big and bulky; consequently, they didn't easily lend themselves to being hung from a wire; they needed to be propped up, an often clumsy operation, not to mention the time spent finding something to do the propping. Another concern with multimeters was their long leads — usually around 36-in. long — which would result in a tangled mess. And the meter's point probe had to either be held on the wire or taped, another inconvenience.
Flashlight-type continuity testers presented similar issues: long leads that got tangled with themselves or other tools in the toolbox, as well as being too heavy to hang from a wire by their three-foot clip leads (especially with the weight of two "D" batteries inside). What's more, because flashlights are round, they tended to roll and fall when they were propped up on a ladder. This would cause either breakage of the flashlight bulb or a dent in a customer's hardwood floor. And although Blanchard was sometimes able to position the flashlight so that he could see it from the room in which he was testing the wire, but the bulbs were invariably so weakly illuminated, that it was still necessary to make a trip back to the room in which the flashlight was positioned, to really be sure that the light was on.
Pocket Pens Even Worse
There were also inexpensive, pen-shaped continuity testers, with a single wire coming out and powered by two penlight batteries. Though they did have some utility as mini-pocket flashlights, they had just one lead; the user had to touch the other wire to the metal flashlight casing, meaning it had to be taped to it or held on the wire by hand, a not-so-minor annoyance.
Blanchard's dissatisfaction with the offerings of his day catalyzed his drive to develop a home-grown solution. After extensive tinkering, he devised a small enclosure that contained a 9-volt battery. The relatively high voltage battery would not only generate a brighter light, it would allow the current to overcome any resistances, the slightest of which can affect continuity measurement. The 9-volt battery would also make the device lighter, which would allow it to support its own weight while clipped to even the thinnest wires.
Blanchard decided to pulse the circuit, so the light would blink on and off. This pulsing conserved electrical energy, while making the light much easier to see from a distance. He also switched to a red, super-bright LED, enhancing the light's visibility even more under virtually all ambient conditions.
Next, he shortened the leads to eight inches, which remedied the tangling problem. He reasoned that the user almost never needed to stretch the leads longer than a foot when measuring continuity. The addition of the remote probe was perhaps the single most significant enhancement. Despite the previous fine-tuning, there were still times when Blanchard was required to walk back and forth between rooms while testing wires. The remote probe alleviated the situation; this two-part system was unambiguous and would provide proof positive when the tester found the proper other end of the wires being tested.
To augment the one-man operation, the inventor added a loud beeper that would pulse in sync with the tester's light. "I could hear it from two to three rooms away," he said.
Adding an IC
Blanchard produced four versions of his invention between 1988 and 1996, including the use of a low-power IC in the third version (1993) and reducing the total number of components in the fourth and final version (1996). In spite of the obvious utility of the new tester, no major companies seemed to want to pursue it further. It took another eight years, when in July 2004, am Extech rep was calling on Standard Electric in Waltham, Mass. During the conversation, the rep was told that an electrician named Joseph Blanchard had done some intriguing things in the area of continuity testing that Extech might want to look into. Extech management did, in fact, contact Blanchard, who pitched his tester and its benefits. While there was some initial skepticism about getting involved in a product geared specifically to the electrical trade, there was enough of an attraction to pursue a mutual business arrangement. "Extech took the unit and copied the circuitry exactly as it was," Blanchard said. "I provided them with all documentation, diagrams, a complete parts list and a working unit. Over the next couple of years, I worked with Extech's engineers and technicians to help tweak the final look of the device and map out its production. Lastly, I wrote the operating manual, and the company's marketing people designed the sales packaging and promo brochures.
Eliminating the Partner
The CT20 Continuity Tester Pro today is a boon to any electrician whose current continuity testing device is causing them fits. This affordable test product, most importantly, eliminates the need for two people to be at opposite ends of the wires during a continuity test. It is a perfect tool not just for electricians, but for cable TV and audio systems installers, alarm technicians, HVAC installers, auto repair technicians, handymen and do-it-yourself homeowners. The CT20 is a two-part system consisting of the master continuity tester/transmitter and a unique two lead, bi-color (red/green) LED Remote Probe. The master Continuity Tester/Transmitter is used for local continuity testing and remote location wiring identification. Using the Remote Probe allows for single-person remote continuity testing — as envisioned by Blanchard — when identifying cables, verifying individual wire polarity labeling and also labeling long-distance wire/cable runs where the other end of the wires are in a different, i.e. "remote," area.
Using the CT20 continuity tester and its remote probe.
The Remote Probe's bright, pulsating LED is visible even in bright daylight areas. The LED flashes green when wiring is properly identified with respect to the polarity of the transmitter unit's color-coded test leads (Polarity Differentiation). The probe LED then flashes red when its leads are attached to the tested wires in reverse order. The master Continuity Tester/Transmitter has a bright flashing LED and a loud pulsating beeper which can be heard over high background noise. This combination of the two parts allows a single user to identify up to three grouped wires or cables at a time for correct labeling, with only one trip to the other end of the wire or cable location. Lightweight and pocket-sized, both parts of the Continuity Tester Pro use alligator clips to enable them to hang from the wires/cables under test.
For more information, contact: Extech Instruments, 285 Bear Hill Rd., Waltham, MA 02451-1064
781-890-7440 fax: 781-890-7864 E-mail: email@example.com Web:
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