Arlyn S. Powell, Jr.
The butt-in test set is perhaps the most basic and widely used piece of test equipment in the telecommunications industry. Looking like a simple telephone handset, it is anything but simple--it can pack a wide range of sophisticated features into its rugged shell.
Its basic function, however, is straightforward. When connected to a telephone line, it can detect transmission loss, noise, opens, shorts and signal quality, as well as other voice-line problems.
Jensen Tools Inc. (Phoenix, AZ) distributes butt-in test sets from a number of manufacturers. According to technical support representative John Tucker, the Dracon Division of Harris Corp. (Camarillo, CA) is the established market leader in butt-in test sets, with a wide range of products for various applications. Less-expensive devices, priced at just over $100, are used indoors in premises applications and do not require the ruggedness or waterproofing offered by outdoor devices. More sophisticated models may cost $300 to $500 or more, and are sold mostly to regional Bell operating companies for central-office and outside-plant use.
Whatever their bells and whistles, however, all butt-in test sets must meet the generic requirements for the craftsperson`s handset, TR-TSY-000344, issued by Bell Communications Research, also known as Bellcore (Livingston, NJ). The principal applications specified by this standard are originating test calls on dual-tone, multiple-frequency and dial-pulse telephones and for testing the switching, continuity and talking features of the line circuit.
Market trends
Jensen`s Tucker sees the market for butt-in test sets today as being application-driven. "The more popular devices that we sell," he says, "are models that have central- office plugs. They will accept a variety of leads--alligator clips, bed-of-nails. This configuration is quite versatile, and gives the technicians flexibility for what they will encounter in the field."
Once the question of application is resolved, the choice of a unit depends on its built-in features. "Our low-end model is designed to be used in-house," says Tucker. "It`s not ruggedized. The next step up has a bit rugged case, but the features are primarily the same. And then we get into some of the higher-end models. The Harris/Dracon TS-22, for example, has an amplifying speaker, so the technician can hear the person at the other end of the line without putting the handset to his head. The TS-22A adds both-ways, hands-free capability, which amplifies the incoming as well as the outgoing signal."
Price does not seem to be a major concern with these devices, but there are two technology trends that are just beginning to demand attention. One is the need for digital units compatible with integrated services digital network, or ISDN, lines. In the past, butt-in test sets have been based strictly on analog technology, since "plain old telephone service" runs over analog lines. ISDN-compatible digital butt-in test sets have recently been introduced by Tektronix Inc. (Beaverton, OR) and Tele-Path Industries (Salem, VA). Chesivale Electronics Corp. (Sedona, AZ) plans to introduce an ISDN unit in the first quarter of 1996.
A second issue is the need to identify digital data lines without interrupting the flow of traffic. Harris/Dracon has recently introduced its Datasafe line of test sets. Says product-line manager Linda Hathorn, "With the growth in use of data lines, butt-in test sets need to be more data-safe. You can accidentally go into talk mode on your test set, disrupting data flow. Or, you may mistakenly identify a data line as a standard voice line, because you can`t hear high-speed data on the line. In such cases, thinking it`s a dead pair, you might cut the line."
With data-lockout test sets, when you go into talk mode, the instrument gives an audible beep if you are clipped to a data line. Also, the device will not draw current from the line, so the data flow is protected. "It`s a safety precaution," Hathorn adds. "The markings may have come off a wire. The records may not have been updated. There may be no way to identify a data line without testing it. We`re trying to provide a more secure procedure to do that."
Bruce Bond, Chesivale`s director of North American marketing, agrees that protecting data is paramount. "The biggest trend in butt-in tests sets right now," he says, "is making them absolutely safe to use on a digital line. The fact is that, with a standard butt-in test set, if you take it off-hook on a data line, you`re going to disrupt the data. The impedance in the unit in the off-hook mode is simply too low to allow digital signals to pass. Even with so-called data-lockout units, the technician may have a problem."
Bond stresses that not all units that claim to fully protect data actually do so. "Saying that a test set does not disrupt data can be misleading," he says. "Such a device may be safe in the monitor, or on-hook, mode, but as soon as the technician takes the unit off-hook, the data is disrupted."
Digalert circuit
Chesivale`s answer to this problem is a series of instruments that is equipped with a circuit called Digalert. "With this circuit," Bond adds, "if you accidentally take the set off-hook, it will give you a warning and lock you out. You actually can`t take the unit off-hook; it will ring an alarm as soon as you make contact with a digital circuit, whether you are in monitor or talk mode."
Bond believes that this feature--automatic disconnection of the test set before it can disrupt a data line--will become the standard in the industry. He says the capability was developed at the request of a regional Bell operating company, which has since adopted the unit. "It has become the standard with Southwestern Bell," Bond claims, "and I think it will become the standard with everybody, as soon as they realize it`s available."
This capability has become vital, not just because of the tremendous growth in the number of digital data lines, but also because of the increasing cost and inconvenience associated with line outages. Data-line disruption has become such a common problem that some common carriers have promised rebates to their business customers if their digital lines are ever accidentally disrupted.
"The [regional Bell operating companies] take the matter very seriously," Bond adds, "but you can`t blame the technician, because he has no way of knowing if it`s a data line. He hears exactly the same thing he would hear on a [plain old telephone service] line--nothing. So he takes the unit off-hook, hoping to get a dialtone. But he doesn`t, because it`s a digital circuit, so we`ve built that foolproof safety net into the device itself."
Manufacturers and users alike agree that, once you have disposed of the major technology issues, durability is the chief concern. Although butt-in test sets may contain sophisticated electronics, they serve as tools in the most demanding of environments. Some are engineered to withstand a 20-foot drop from a utility pole. Others are waterproof. (For a discussion of other features, see "Features to Look for in Butt-in Test Sets," page 8.)
Says Chesivale`s Bond, "It`s a piece of rather sophisticated electronics that gets hung on a toolbelt alongside a cast-iron lug wrench--and it gets treated the same way."
Because of the widespread need for butt-in test sets, the market is large--with an installed base of close to 300,000 units by one estimate. What is more surprising, given the perception that these are simple analog devices, is that the market is growing. Although hard numbers are difficult to come by, one industry watcher estimates that the market has tripled over the last 15 years.
Harris/Dracon`s Hathorn has a similar view of the market. "What we`re finding," she says, "is that there are more and more people entering the market from different areas--not necessarily from the [regional Bell operating companies]. There are more independent contractors, more electricians, people who haven`t used test sets before. While the [regional Bell operating companies] may be moving into fiber, there`s still a huge amount of copper that needs to be maintained."
Butt-in test sets must be durable to meet the Bell Communications Research, or Bellcore, standard. Harris/Dracon manufactures units to be used outdoors that must be able to withstand a 20-foot drop. These devices can also be used in the rain, and they have built-in surge protection in case of lightning strikes.
Features to look for in Butt-in Test Sets
Technicians need a means of communicating over voice lines with other craftspeople. They also need a simple device to verify whether a voice line is functioning. These are the basic functions of the butt-in test set, according to Kurt Foulger, engineering manager for the test-set product line at the Dracon Division of Harris Corp. (Camarillo, CA).
Harris/Dracon, with 10 different models in its product line, has perhaps the widest variety of these test sets in the marketplace. Foulger has identified some of the features and functions you may want to consider when shopping for a butt-in test set:
Amplified speaker?This feature allows a technician to hear incoming messages from the test set while working nearby. It amplifies incoming calls only, and is not two-way.
Hands-free, two-way speakerphone?This feature lets the technician hang the set from a cable or rack and work with both hands while talking with a craftsperson at the other end of the line. Since technicians are frequently put on hold, this feature lets you go on with your other work without having a handset jammed between ear and shoulder. This feature differs from the amplified speaker mode in that amplified messages pass both ways, and not just in one direction.
Polarity indicator?Most butt-in test sets have a polarity indicator that identifies the polarity of the line. Many telephone systems today are designed to work in either of two polarities, but some older systems require a single polarity, so craftspeople must be able to test for this characteristic. An indicator on the test set tells whether the voice line is of normal polarity, which is negative on ring, or reverse polarity, which is positive.
Last-number redial?A redial button allows the last number dialed to be redialed, a feature common on telephone handsets.
Memory store and recall?A phone number can be stored in memory, so that it can be recalled throughout the work day. This is useful, for example, in accessing voice-response devices at the central office. It is different from last-number redial, in that several numbers can be stored in memory and recalled using a recall button and a number button on the keypad. A store key is used to store the number into the memory register.
Pause button?Many private branch exchanges require a pause between the time an outside line is requested and the start of dialing an outside number. A PBX pause button puts in a pause of several seconds that can be entered into memory.
Mute switch?This allows the technician to turn off the transmitter in a noisy environment, so that background noise is not transmitted to the craftsperson at the other end of the line, nor is it fed back to the technician making the call. The mute switch must be turned off when the technician is talking.
Accidental transient protection?It is not uncommon to get lightning surges on phone lines. Transient protection safeguards not only the user, but the test set as well. It functions like a built-in surge protector, electronically opening the impedance to reduce current flow. The receiver must also have an acoustic-level limiter that prevents transients on the line from being converted into very loud signals, a requirement of the Bellcore test-set specification.
Hearing-aid compatibility?The receiver element of the handset is manufactured to produce a strong enough magnetic field to couple into a hearing aid. Many hearing aids have both acoustic and magnetic-
coupling modes, and can be switched back and forth between them. Magnetic coupling improves reception and reduces feedback.