. The Bell System technical journal . Fig. 1—-High impedance toll cord for toll switchboard No. 1 In the No. 3 switchboard the ringing relay and the direct-currentsupervisory relay, which were formerly connected across the tip andring conductors of the cord circuit, have been moved from the cord tothe line and switching trunk, respectively, and the cord circuit has beensimplified as is illustrated in Fig. 2. In this board the line and trunk. To Positional CKt. Fig. 2—Toll cord for toll switchboard No. 3 signals are transferred to the cord over the sleeve circuits. This isaccomplished by using
. The Bell System technical journal . Fig. 1—-High impedance toll cord for toll switchboard No. 1 In the No. 3 switchboard the ringing relay and the direct-currentsupervisory relay, which were formerly connected across the tip andring conductors of the cord circuit, have been moved from the cord tothe line and switching trunk, respectively, and the cord circuit has beensimplified as is illustrated in Fig. 2. In this board the line and trunk. To Positional CKt. Fig. 2—Toll cord for toll switchboard No. 3 signals are transferred to the cord over the sleeve circuits. This isaccomplished by using a nominal sleeve resistance of 1,800 ohms forthe line and trunk circuits and connecting the lamps in the sleeves of thecord. Under these conditions there is not sufficient current flowing inthe sleeve to light the lamp, but when a ringing signal is received over aline and a cord is associated with that line or when a receiver-on-the- 20 BELL SYSTEM TECHNICAL JOURNAL hook signal is received over a switching trunk, the sleeve resistance ofthe hne or trunk is changed from 1,800 ohms to 80 ohms, which in-creases the current in the sleeve of the cord sufficiently to light thelamp. Line Relay Functions in Twofold Capacity The majority of toll lines in the plant today are of the ringdowntype and the operator at one end calls the operator at the distant endby ringing over the line. To receive this ringing signal in the No. 1board, the line
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
