US2588767A - Electrical signaling system - Google Patents

Description

March 11, 1952 P. N. ROSEBY ELECTRICAL SIGNALING SYSTEM 2 SHEETS-SHEET 1 Filed April 8, 1946 .I/vvewroR PHILIPYN.

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Patented Mar. 11, 1952 ELECTRICAL SIGNALING SYSTEM Philip Norton Roseby, Liverpool, England, assignor to Automatic Telephone & Electric Company Limited, Liverpool, England, a British company Application April 8, 1946, Serial No. 660,333 In Great Britain May 19, 1945 2 Claims. l

The present invention relates to electrical signalling systems and apparatus for use therein and is more particularly concerned with systems of the type in which signalling is effected by the use of high frequency currents superimposed on electric supply mains. It will be understood that the expression high frequency currents as used herein implies that the currents concerned are of a frequency which is high compared with the power frequency, for instance, audio frequency, and is not intended to be limited to high frequency currents as normally understood in the radio art.

Systems of this general type are already well known and an example is disclosed in British Patent No. 566,122, in which the arrangements are such that signals ,intended to produce different eifects all comprise currents of the same high frequency to which the responding equipment is tuned but the dilferent effects are produced by interrupting these currents with a characteristic rhythm or cadence which is different for each signal. The above-mentioned specification moreover is concerned with asystem in which in order to reduce the possibility of false operation by parasitic currents, each operative signal is preceded by a preliminary signal of a different cadence, the effect of which is to render the equipment responsive to the operative signals subsequently transmitted. The preliminary signal is transmitted for a sufficient length of time to operate a thermal switch which then effects the necessary circuit change-over and the operative signal is then transmitted while the circuits remain in this condition during the cooling period of the thermal switch.

I It has been found in practice that with an arrangement of this type the operating period of the thermal switch may not be sufficiently definite as it is dependent on the closing of the heating circuit intermittently by a relay of the galvanometer type and the chief object of the present invention is to produce an arrangement which shall be more reliable in operation while working on the same general principles and giving as good or better protection against parasitics.

According to one feature of the invention in an electrical signalling system employing high frequency currents superimposed on electric supply mains, false operation by parasitic currents is prevented by arranging that the equipment which responds to the characteristic signal corresponding to the switching operation it is on the receipt of a preliminary signal of different characteristics and is then rendered ineffective after a predetermined interval.

According to another feature of the invention in an electrical signalling system employing high frequency currents superimposed on electric supply mains, in response to a preliminary signal of different characteristics from those of the signal producing the desired switching operation the equipment for responding to the said operative signal is rendered effective and remains in that condition for a predetermined time independent of any further transmission of the preliminary signal.

A further feature of the invention is that in a responding unit for use in electrical signalling systems employing high frequency currents superimposed on electric supply mains, equipment responsive to a preliminary signal of different characteristics from those of any signals employed for effecting switching operations is arranged on operation to render effective equipment adapted to respond to one or more operative signals and to initiate the operation of a timing device which after a predetermined time renders ineffective the equipment responsive to operative signals.

The invention will be better understood from the following description of one method of carrying it into efiect which should be taken in conjunction with the accompanying drawings, comprising Figs. 1 to 3. Fig. 1 is a circuit diagram of a single responding unit while Figs. 2 and 3 show respectively front and side elevations of a responding unit in accordance with the invention.

Considering first the circuit arrangement of Fig. 1, it is assumed that signalling is being effected over a three-phase four-wire network with line conductors Ll--L3 and neutral conductor N. The method of applying the signalling currents is assumed to be such that the signalling currents appear at substantially equal strength on the different phase leads o that the responding units may be connected to any one of these leads as is most convenient. It will be seen that the responding unit illustrated is connected between the phase lead L3 and the neutral conductor N and the signalling currents are supplied to an acceptor type filter LFC comprising an inductor Ll and capacitor CI in the primary circuit and an inductor L2 and capacitor C2 in the secondary circuit, the inductors being loosely coupled and the values of the components being chosen so that a broadtuning effect is obtained to the signalling frequency. From the secondary circuit connection is extended to a rectifier bridge BR, the output of which is shunted by a further rectifier LR which serves for limiting purposes and avoids any danger of the equipment being damaged by strong signalling currents such as may be received by a responding unit located in close proximity to the transmitting point. The incoming signalling energy is then fed over normally closed contacts TS2 to the winding G of the oscillating movement responsive to the preliminary signal.

Each of the three oscillating movements G, GA and GB is of the general type disclosed in British Patent No. 518,877, and comprises essentially a length of wire carrying one or more permanent magnets which is located in the field of an operating coil to which the rectifier signalling currents are fed. The magnets are loaded so as to oscillate at a predetermined frequency which will be difierent for each switching operation catered ior, and when the oscillations attain a given amplitude a suitable con tact closure is effected.

Accordingly when the preliminary signal is received, the movement G responsive thereto is set in operation and after a short interval closes its contacts GI thereby energising the electromagnet S from the mains. As will be more clearly understood from the description of the actual construction as shown in Figs. 2 and 3, the energisation of magnet S changes over contacts TS! and T82 and these contacts then remain in the operated position until they are restored by means of a thermal switch. The closing of contacts TSLene -gises therheating coil H of the switch TS whereby the" movement of a bimetallic strip is initiated. Contacts T52 disconnect the winding G and connect up in its place windings GA and GB in series. These are assumed to control complementary switching operations, for instance, the switching on and off of street lights in response to signals of different rhythms or cadences. The preliminary signal persists for a short time only and thereafter the operative signal is transmitted and this will be assumed to be of such rhythm as to operate effectively the movement having the winding GB. When the signal has persisted for long enough to build up the necessary oscillation of the associated movement, contacts GBI close and a circuit is completed for the right-hand coil W2 of the mechanically-locking contactor MLC. Thereupon the mains are connected over the armature A to the terminals TI and T2 to which the load is assumed to be connected so that in this case the street light is switched on. Shortly thereafter the thermal switch completes its operation and restores the contacts TS! and T52 to their original position thereby disconnecting the heating coil H and hence even if the operative signal persists, no further effect is produced on the responding equipment since this signal will not be of a suitable rhythm to operate the unit G.

When itis desired to switch the lights off, the

4 stored to the position shown in which the load is disconnected. V

A detailed description will now be given of a suitable mechanical construction for the responding unit as shown in Figs. 2 and 3, Fig. 2 being a front elevation and Fig. 3 a side elevation in which the apparatus which is situated on the back of the base plate has been omitted.

On the front of the insulating base plate ID are mounted the three oscillating movements or rhythm relays G, GA and GB together with the electromagnet S, thermal switch TS, and capacitor CI. The remaining components are mounted on the back of the base plate for instance in the general manner disclosed in British Patent No. 524,685.

Considering now a rhythm relay such as GB in more detail, it is assembled on an individual metal base II which is secured to the main base plate [0 by screws such as 12 and I3, and has a galvanometer type movement involving a pair of small permanent magnets such as Hi, which are clamped with like poles adjacent on opposite sides of a stretched wire It: by means of a pair of nuts (not shown) which are carried on the screwed rod I 6 through a central hole in which the stretched wire extends. The wire 15 may comprise a strip of rustless material such as nickel-chromium alloy, and is secured at each end to two projecting lugs ii and it on the base plate H. Also secured to the base plate H is a synthetic resin coil former H) which carries the energising coil 29, the wire l5 extending freely through suitable holes in the sides of the former l9. The stretched wire carries near to its lower end an electric contact-making member 2| which is adapted, when the oscillating movement attains its full amplitude to effect electrical connection with the adjustable fixed contact member 22 which is mounted on a biock 23 secured to the base I l, the pair of contacts 2! and 22 also being together designated contacts GBI. Tuning of the relay to the required rhythm is efiected by means of adjustable balance weights in the form of nuts such as 2 and 25 which are carried on the rod l6. Electrical connection with the moving contact 2! is had via the wire I5, lug I! and tag 26 on the base ll, while connection with the coil 20 is had via wiring tags 21 and 28.

The electromagnet S and thermal switch TS are mounted on a common base-plate 30 which is secured to the main base plate 50 by screws such as 3! and 322. The U-shaped yoke 33 of the electrcmagnet is secured to a projecting lug on the base plate 39 by screws 34 and 35 and carries the coil 36 which is provided with wiring tags 37! and 38. Through the hollow core of the coil extends the plunger 39 which terminates at one end in a circular magnetic plate 49 which is attracted towards the yoke when the coil is energised. The other end of the plunger is normally in engagement with the upper blade ii of a pair of blades M and 52 which, by virtue of the helical linking spring 43 are urged into V notches in the horizontal upper portion of the bracket 44 so as to cause them to function with a toggle action. The lower blade 42 is provided with contacts and forms the moving element of the changeover spring set TSZ; The upper blade M on being moved over from its normal position (shown dotted) to the operated position, engages with the roller 45 of the moving spring of the spring set TS! and so closes these contacts, whereupon an electric circuit-iscompleted to the thermal switch heater winding H which is wound on a bi-metal strip. At the same time contacts TS2 are operated to connect relays GA and GB to the tuned circuit. The heater H in due course causes the bi-metal strip to deflect to the left and in so doing to carry with it the sprin set TSI via the intermediary of the insulating buffer 46. The upper tog le switch blade 4| is also moved until it passes its dead centre position with respect to the lower blade 42, whereupon the blade 4| will snap over into the normal position shown dotted. The contacts TSI and T82 will then be restored to their normal positions and the circuit to the heater winding H of the thermal switch TS will be opened and the preliminary rhythm relay G will be reconnected to the tuned circuit. Electrical connection to the contacts T32 and TSI and to the heater H is had via wiring tags "-52.

The invention therefore provides a very simple and compact construction of responding unit which may be made extremely sensitive to signalling currents and yet highly selective so as to respond only to those intended for its operation.

I claim:

1. In an electrical signalling system for effecting the remote control of a plurality of devices by high frequency currents superimposed on electric supply mains, first means associated with each device and responsive to signalling currents of one character, second means associated with each device and responsive to signalling currents of a diiferent character, an electromagnet energized on the operation of said first means, a blade pivoted about one end, means operated by said electromagnet for moving said blade about its pivot, a second blade substantially in line with said first blade and pivoted about its end adjacent to the pivot point for said first blade, a tension spring connecting said blades substantially along the line of their length whereby when said first blade is moved by said electromagnet said second blade will move past its dead center position, means operated by said first blade for energizing a thermally operated switching means, contacts carried by said second blade for disconnecting said first responding means and connecting up said second responding means, and means operated by said thermally operated switchin means for moving said first blade back to its original position whereby said thermally operated switching means is deenergized and said second blade is moved to connect up said first responding means again in place of said second responding means.

2. In an electrical signalling system for effecting the remote control of a plurality of devices by high frequency currents superimposed on electric supply mains, first means associated with each device and responsive to signalling currents of one character, second means associated with each device and responsive to signalling currents of a different character, an electromagnet energized on the operation of said first means, first contacts operated by said electromagnet for disconnecting said first means and connectin up said second means and second contacts controlled by said electromagnet for energizing thermally-operated switching means, said thermally-operated switching means being arranged to restore said first and second contacts to their original condition after a predetermined time, said means responsive to signalling currents comprising a permanent magnet supported on a stretched wire so as to be capable of torsional oscillations, a coil encircling said magnet, circuit arrangements for feeding signalling currents to said coil, and contacts operated when said magnet attains a predetermined amplitude of swing.

PHILIP NORTON ROSEBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,714,967 Wensley May 28, 1929 2,131,164 Chauveau Sept. 27, 1938 2,255,162 Hart Sept. 9, 1941 2,394,786 Korneke Feb. 12, 1946

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