Patent GB-1423279-A (GB)
Title: Automatic testing apparatus for telecommunications lines
IPC: H04M3/28
Filed: 1973-12-14
Abstract: 1423279 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 14 Dec 1973 [18 Dec 1972] 58020/73 Heading H4K In a testing arrangement for subscriber lines, each test is performed simultaneously on a plurality of lines, preferably four lines. The tests are for false grounds, foreign battery and leakage current. The lines are connected to an exchange of the "Al cross-bar" type disclosed in USA Specification 3,441,667 and all the lines of the exchange are tested in sequence, four at a time, under the control of a central processor CPU. The matrix locations of lines that fail are printed out by a printer TTY. The testing circuit 500 utilizes transistors, operational amplifiers and Zener diodes and operates by comprising a voltage on a line with a fixed reference voltage. A double seizure detector includes thyristors in a timing circuit. A visual display utilizes L.E.D.'S. In operation the central processor supplies markings to the controller 200 (detailed in Fig. 2, not shown) to cause the operation in sequence of a frame group, a line cut and a switch test relay to access a particular switch. A routine is then performed to check whether a marker is working in the particular line unit. If the check is positive a check is made every 10 seconds for up to 3 minutes for an indication of marker release, and if the marker still has access after this time a message is typed to indicate that the line unit is to be skipped. If the unit is free, a horizontal level of the switch is accessed by the operation of a further test relay to give access to four line circuits and the lines are cut through to the test connector 400 (detailed in Fig. 4, not shown). A second marker activity check is made, and the four lines are tested for busy, using a high impedance probe, e.g. a mercury relay which responds to ground or the sleeve level, idle lines being cut through to the test circuit (Fig. 5) and being busied. The horizontal level is skipped only if all four lines are busy. LED'S on the panel control 600 (detailed in Fig. 6, not shown) are lit to indicate the frame group, line unit, switch and horizontal level of the lines under test. In Fig. 5, the detector 530 and the line connect and conditioning circuit 505 are duplicated four times. To perform a test a particular resistance range for the test is chosen by the processor using circuit 520 and the lines are conditioned using relays GWD, BAT, LP, LC, CON. Each test is performed by charging the line capacitance, with the wires connected in a particular manner, to a particular voltage. The voltage is given time to change and it is then compared against a reference voltage using circuit 530. If the voltage difference is above a predetermined level the output of differential amplifier swings to operate a transistor Q1 thereby giving a failure indication. The panel control 600 includes a double seizure detector which is activated if two frame group test relays or two line unit test relays are simultaneously operated. In such an eventuality an alarm is sounded and the identity of the group or unit which the processor is trying to access is typed out. The processor includes a test/no test map for lines expected to fail e.g. coin boxes, PBX's to prevent unwanted print-out for such lines. The test circuits may be modified to provide for statistical metering.