Patent GB-826383-A (GB)
Abstract: 826,383. Electric selective signalling. SHAXD & JURS CO. April 23, 1956 [May 6, 1955], No. 12411/56. Class 40 (1). In a system of the type described in Specification 826,384 wherein a reading station is connected via a line or radio link through one or more remote selecting apparatuses to a plurality of transmitters situated at remotely located tanks which transmit information relating to liquid level &c., the remote selecting apparatus comprises a stepping switch S10 operated by stepping coil H and a time delay device TD4. Some of the terminals of S10 are connected direct to transmitters 12, the remaining terminals being connected to further remote selecting apparatuses to which are connected remote transmitters 12. Selecting pulses sent over line 21 from the reading station are followed by relay G which in turn energizes step coil H and the wiper of S10 is advanced to a terminal equal to the number of pulses sent over line 21. As soon as the wiper moves from terminal O, offnormal contacts 1, 2 close, and energize slowacting relay I which is not operated during the reception of selecting pulses because the circuit is periodically interrupted by contacts 1, 2 of step coil H. A predetermined interval after the selecting pulses cease, relay I operates, whereby the start pulse from the reading station is transmitted via contacts 2, 3 of I to the selected transmitter 12, and the motor of time delay device TD4 is energized. Opening of contacts 4, 5 of I prevents operation of relay G by the start pulse. After the start pulse has been transmitted the transmitter 12 sends confirming code pulses and information pulses relating to the liquid level, and after a predetermined time during which this information has been transmitted, the time delay device TD4 closes its contacts 2, 3 to energize step coil H and return S10 to its home position. Relay I does not release until S10 has homed. Release of I disconnects line 21 from the wiper of S10, reconnects line 21 to relay G and de-energizes the motor of TD4, and the apparatus is now ready for operation by a further series of selecting pulses. Transmitters connected to further remote selecting apparatuses connected to the terminals of S10 may be selected by sending a first series of pulses to select the correct terminal on S10, and a second series of pulses which via the selected terminal on S10 operate the remote selecting apparatus connected to this terminal in the manner described. In a modification, Fig. 3 (not shown) in which a second series of pulses is required both for the selection of a local transmitter, or the selection of a transmitter via a further remote selecting apparatus, an additional relay is provided which is connected between contact 1 of relay I and earth. The first nine terminals of S10 are used for the selection of further remote selecting apparatuses as already described, but if it is desired to select a local transmitter the first series, of ten pulses, steps S10 to terminal 10 which is connected to the negative side of the power supply and provides an energizing circuit for the additional relay, which picks up and prevents the operation of relay I. The second series of pulses then steps S10 to the appropriate terminal 11, 12, &c., for the desired local transmitter, and releases the extra relay. The apparatus then operates as previously described. If for some reason the second series of pulses is not received the wiper of S10 will be on terminal 10 and the additional relay closes contacts to energize TD4 to return the apparatus to the home position. Specification 741,622 also is referred to.