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Active Loop Test Device

IP.com Disclosure Number: IPCOM000052873D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Related People

Bonner, BR: AUTHOR [+3]

Abstract

This article shows how a loop communication system having a main loop and an alternate loop for fault bypass can be tested by one person using two test boxes. Each test box contains a transmitter and receiver operating at normal loop frequencies. The tester can detect crossed cable wiring at each terminal connection point, that is, the upstream loop cable segment erroneously wired to the downstream connecting terminals.

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Active Loop Test Device

This article shows how a loop communication system having a main loop and an alternate loop for fault bypass can be tested by one person using two test boxes. Each test box contains a transmitter and receiver operating at normal loop frequencies. The tester can detect crossed cable wiring at each terminal connection point, that is, the upstream loop cable segment erroneously wired to the downstream connecting terminals.

Figs. 1 through 4 show how the loop wrap switches are controlled when using the tester of Fig. 5. Fig. 1 shows the loop ready to test, all loop station connectors being switched to the wrap position and a tester connected to the terminals at loop station connector A.

Fig. 2 shows the loop tester testing the downstream main and auxiliary loop segments 11 and 12 for continuity. If the cable had been crossed at loop station connector A (instead of station C as shown, for example), tester Tl would be testing upstream loop main and auxiliary segments 15 and 16, respectively, for continuity and at this point would not detect the wiring error.

Fig. 3 shows tester 2 connected at loop station connector B in communication with tester 1. At this time, crossed wires at loop station connector A or loop station connector B will be detectable because signals could not be transmitted between testers T1 and T2. If the testers cannot communicate, the test person can interchange the cable wires at loop station connector B. If this change does not correct the problem, the wires will be returned to their original position and the test person must walk back to loop station connector A and interchange the wires at that station connector. It will be noted that since tester Tl did achieve communication between its transmitter and receiver, failure to transmit between T1 and T2 must be caused by crossed cable wiring.

After achieving communication between testers T1 and T2, the test person switches loop station connector B to pass position, as shown in Fig. 4, and moves tester T2 to loop station connector C to repeat the test procedure at C. Wires 11 and 12 will then be connected to wires 13 and 14, respectively.

Rerring to Fig.5, a detailed logic diagram of each tester is shown. Transmitter-Receive module 21 transmits a continuous stream of binary 1 bits under control of oscillator 23.

The receive portion of module 21 receives binary 1 bits transmitted through the wires of the loop and provides an input signal to AND gate 25. If all wires of the loop cables are firmly connected and no shield current is flowing, detector 27 will not detect shield current, permitting inverter 29 also to provide a signal to gate 25. AND gate 25 will, therefore, provide a signal to single-shot 31, causing the Q output of single-shot 31 to rise to a plus voltage and the not Q output of single-shot 31 to go to zero volts. Single-shot 31 converts the 9.6 KHz pulses to a DC level. Because the red and green indicators are returned to a positi...