. The Bell System technical journal . ntrols thesequence of test operations and is hung on pins over the field of 1,000spring plungers (20 X 50) as a part of the setup operation for a particu-lar relay unit. Closing the door and screwing up the hand wheel, whichis necessary to provide the force required to depress the plungers, willground those which coincide with holes in that particular card. Cross-connection setup of the test leads is achieved by the use of aplug-board such as is commonly used for quick change over on perforatedcard type business machines. Fig. 6 shows the plug board being
. The Bell System technical journal . ntrols thesequence of test operations and is hung on pins over the field of 1,000spring plungers (20 X 50) as a part of the setup operation for a particu-lar relay unit. Closing the door and screwing up the hand wheel, whichis necessary to provide the force required to depress the plungers, willground those which coincide with holes in that particular card. Cross-connection setup of the test leads is achieved by the use of aplug-board such as is commonly used for quick change over on perforatedcard type business machines. Fig. 6 shows the plug board being insertedinto the transport mechanism. The relatively large number of terminalsare retjuired because each of 60 test leads must be capable of beingpatched in to an equi\alent number of terminals on a maximum of tendifferent circuits. Not all of our test sets are equipped with the uppercabinet since most key units have only one circuit and on these a simpler * Patent No. 2,329,491. 1162 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956. Fig. 5 — Rear view of Card-0-Matic test set showing insertion of perforated card. cross connection fixture is plugged into the location where the lowerend of the cable joining the two cabinets is shown terminated in Fig. side view of the test set is shown in Fig. 7 to give an indication ofthe amount of switching e([uipinent and wiring necessary for an auto-matic test set of this sort. The set is powered from a r20-\olt 60-cy(le AUTOMATIC TESTING OF RELAY SWITCHING CIRCNITS 1163 source from which are derived the 24-volt dc, 90-volt 20-cycle ringingcurrent and 600-cycle audio tone supplies that are required. The testcircuit features mchide tone transmission checking, dial pulsing, 90-volt20-cycle ringing and ground and batter}^ supplied either directly or underrelay control. Other battery and ground relays are available for checkingthe response of the circuit under test. These test features have been sufficient to perform operation tests onmos
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