Patent GB-546928-A (GB)
Title: Improvements relating to level regulating arrangements for electric signal transmission systems
IPC: H04B3/10
Filed: 1941-08-15
Abstract: 546,928. Automatic volume control systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 15, 1941, No. 10402. Convention date, Aug. 22, 1940. [Class 40 (iv)] In a repeating system with automatic volume control and alarm circuits for indicating abnormal level conditions, due e.g. to storms or ice on the lines, drain on the battery, particularly at unattended stations, which supplies the control and a part of the alarm circuits is reduced during abnormal conditions by arranging that the battery is periodically cut off and restored for short testing periods. The unattended station equipment shown in Fig. 1 comprises a line 1 with amplifier 4 and filters forming part of a carrier transmission system, a pilot frequency being diverted at 5 and, after rectification, supplied to volume control and alarm relays 9, 10. These relays have normally central contacts displaced under' control of winding 7 or 8 to one side or the other where they remain until restored by a plunger operated by winding 12. The volume control relay'9 is sensitive and responds to Œ .5 decibel whereas the alarm relay 10 requires a variation of +3 or -5 decibels. The control and part of alarm circuits are supplied by battery 22, other alarm circuits being supplied by the amplifier H.T. battery 39, 45, 48, 58. Volume control. Relay 9 on closing its right hand contact operates relay 20 which connects an A.C. source 17 to motor 15 which adjusts impedances in the line circuit. After 4 seconds, 29 pulls up and operates the restoring winding 12 of the relay 9, but if the transmission conditions are not fully compensated, 9 operates again and effects further compensation in a similar manner. If relay 9 closes its left hand contacts due to variation of level in the opposite sense, a relay (not shown) similar to 20 operates a reverse drive motor 16, or a single reversible motor may be used. Alarm arrangements. Abnormal level variations in either sense operate relays 10 and 30 (quickly) followed by 26 which disconnects the volume regulator and lights an individual lamp 31 for the notice of an attendant if present. After 25 seconds, relay 35 pulls up followed by 36. So far a small 20 volt battery 22 has provided the necessary voltage supply. When 35 and 36 operate, 23 pulls up quickly over a 150 volt battery circuit to disconnect the 20 volt battery, 43 pulls up quickly to bring in a local group alarm lamp 50 and the alarm 53 at a distant attended station, and a circuit for relay 40 operating after 3 minutes is completed. When the last-mentioned relay operates, 23 falls back to re-connect 20 volt battery 22 to the alarm circuits individual to the repeater, but slow to release relay 43 maintains the group and distant alarms for a further period of 35 seconds. The regulating and alarm initiating relays 9, 10 are restored to normal by the. energization of windings 12 when 29 operates on re-connection of battery 22, and, if in the meantime, the abnormal condition has passed, the regulating circuit operates in normal fashion and 43 falls back to disconnect the group and distant alarms. If not, alarm relay 10 starts a further cycle of operations and 43 remains operated. The 20 volt battery is therefore disconnected for the major portion of the time. If the main station attendant desires volume regulation to proceed during the abnormal condition, he throws key 59 to operate relay 40 which releases 23 to re-connect the 20 volt battery and shunts the left-hand contacts of relay 26 to remove the disablement of the regulator. Relay 41 is in any case released after 20-30 minutes by a slowly operating relay 57. Similar arrangements are provided at an attended station, Fig. 2 (not shown), except that relays 30, 26 are maintained operated to light the individual alarm lamp continuously.