Testing for data lines

Sept. 1, 1995
As the number of digital data lines increases, it becomes more important to test for them. If a technician, however, attaches a piece of test equipment to a data line, mistaking it for a standard voice line, the result is a spike or glitch on the data line. This cord makes the data unusable and dumps the entire transmission.

Linda Hathorn, Dracon Division of Harris Corp.

Problem

As the number of digital data lines increases, it becomes more important to test for them. If a technician, however, attaches a piece of test equipment to a data line, mistaking it for a standard voice line, the result is a spike or glitch on the data line. This cord makes the data unusable and dumps the entire transmission.

Solution

To locate twisted-pair data lines and keep them separate from analog telephone service, the technician can use portable test equipment, including butt-in test sets and data probes.

One solution is to use a data probe and a high-impedance butt-in test set, which prevents the technician from accidentally disturbing data traffic. The high-impedance monitor on the butt-in test set lets the technician clip on to a data line unobtrusively, without disturbing traffic. The data probe isolates a data line from hundreds of standard telephone service lines.

Another solution is to use a butt-in test set that can detect digital signals when they are connected to a data line. This device also prevents technicians from going off-hook (getting a dial tone when butting into the line and interrupting the data) and drawing current from the line, should they accidentally try to get a dial tone on a digital line.

Procedure

If you are using a data probe, the following procedure applies:

1) Depress the "on" button and place the tip of the probe between a pair of conductors.

2) If data is detected, the probe emits an audible signal or tone and activates a corresponding light-emitting diode, indicating either 56-kilobit-per-second or 1.544-megabit-per-second data transmission.

3) Once it has been determined that this is a data line, you can continue working around the line, without interrupting customer service.

If you are using a data-detection test set, the following procedure applies:

1) Use the butt-in test set as you would a standard device of this type.

2) When you attempt to butt into a pair of wires but go off-hook, you will hear a beep warning that data is on the line.

3) The test set does not allow you to go off-hook automatically on a digital line, eliminating disruption of the data stream.

If you then clip on to a standard analog telephone line, no reset is needed.

Click here to enlarge image

Using a butt-in test set and a data probe makes it possible to test for a digital data line without disturbing data on a line.

Linda Hathorn is marketing manager for portable test equipment at the Dracon Division of Harris Corp., Camarillo, CA.

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