Patent GB-866654-A (GB)
Title: A method and a system of remote operation and indication
IPC: G08C25/00
Filed: 1959-06-29
Abstract: 866,654. Electric selective signalling systems. ALLMANNA SVENSKA ELEKTRISKA A.B. June 29, 1959 [July 1, 1958], No. 22171/59. Class 40 (1). In a selective signalling system for transmitting data concerning a plurality of devices at a remote station to a central station each item of data is represented by a combination of long and short intervals in a train of pulses, the pulses themselves being alternately long and short so that transmission errors can be reduced. The embodiment described comprises a remote station, Fig. 4, for transmitting ten items of data to a central station, each item of data being represented at the remote station by the combinational states of a pair of relays A1-A10, and by a pair of intervals in the transmitted pulse train, Fig. 1, which commences with a start interval FJ. The pulse train is produced at the remote station by an oscillator comprising two relays T1 and T2, relay T1 determining the length of the pulses and relay T2 the length of the intervals. Relay T1 has associated with it two parallel circuits which control its time of release, one comprising a resistor R1 and the other a resistor R2 and capacitor C1, this second circuit only being effective on oddnumbered positions of a stepping-switch VS. The relay T2 also has two associated parallel circuits R3, and R4 and C2, the latter only being effective when a contact PFa is closed which is when a long interval has to be transmitted. In operation when any of the relays A1-A10 change their states a normally-energized relay S drops out; its contact Sb opens (all contacts are shown in the Figure with their associated relays de-energized) which causes the relays T1 and T2 to produce the desired pulse train. Relays T1 and T2 are both normally energized in their quiescent states. When contact Sb opens relay T1 too drops out after a delay caused by R1. Drop-out of relay T1 opens its contact T1d, thereby initiating the start interval FJ, Fig. 1, and also its contact T1b which de-energizes relay T2. Relay T2 drops out after a delay caused by resistor R3 (contact PFa being open as the stepping switch VS is in its O position) and in quick succession relay T1 picks up via contact T2a causing the advance of the stepping switch by contact T1c, and relay T2 picks up via contact T1b. This occurs at the end of the start interval and at the commencement of the first long pulse. Relays T1 and T2 are now again both energized, as they were initially, and relay S is still de-energized so a further cycle occurs as before. This time, however, as the stepping- switch VS has advanced to position 1 relay T1 is paralleled by both resistor R1 and resistor R2 and capacity C1 so that relay T1 takes a long time to drop out, thereby producing a long pulse (this being the first long pulse in interval 1, Fig. 1). This continues until the stepping switch VS reaches position 21 when relay S is energized, stepping the oscillations of relays T1 and T2 and the stepping switch then advances itself to its home or zero position. A receiver is described (Fig. 5, not shown) in which each incoming pulse advances a stepping switch providing the pulses are alternately long and short, this being determined by the use of a relay with a release time longer than a short pulse but shorter than a long pulse. If the pulses are not alternately long and short then no registration is made at the receiver and the transmitter has to repeat the entire pulse train. It is stated that a series of alternately long and short pulses significant by their number could be used as call signals for calling field stations but no such system is described.