Patent GB-410523-A (GB)
Title: Apparatus for automatically receiving and recording alarm signals transmitted by radio
IPC: H04L15/26
Filed: 1932-11-24
Abstract: 410,523. Selectors responsive to code signals. STANDARD TELEPHONES & CABLES, Ltd., Connaught House, Aldwych, London.-(Deakin, G., Giroud, P., Schreiber, L. J. J., and Chevigny, G. P. ; 46, Avenue de Breteuil, Paris.) Nov. 24, 1932, Nos. 33239 and 35547. [Class 40 (iv).] A code signal receiver adapted to respond only to a predetermined series of signals (dashes) and spaces comprises means for determining whether the length of each dash is within certain limits, and further means for measuring the combined length of at least two elements, e.g. a space and a dash, following a dash of correct length, the signal series being rejected if this length does not lie within certain limits. The length of the spaces is thus checked indirectly only. In one arrangement, Fig. 4, fully described below, two rotary timemeasuring devices N<1>1, N2 are started up when a dash comes in, N<1>1 checks the length of each dash and restores to normal after a correct dash which is recorded on a relay chain. N2 also restores to normal after the first dash, if correct, and immediately re-starts and continues rotating to measure the combined length of the succeeding space, dash, space, dash, elements, the series being rejected if this length is less than a certain minimum. In a modification, Fig. 1 (not shown), N2 does not start until a correct dash has been received. In another modification, Fig. 2 (not shown), N2 also starts rotating after a correct dash, and in one continuous movement measures the combined length (1) of the first space and second dash and (2) of the first and second spaces and second and third dashes, the signal series being rejected if either of these lengths is not within certain limits. The circuits of the second and third relays of the recording chain are dependent on the positions of both N<1>1 and N2 at the time when the second and third dashes should end. In a further modification, Fig. 3 (not shown), of the lastmentioned arrangement, N2 restores at the end of the second dash if the combined length of the first space and second dash is acceptable and immediately restarts to check the combined length of the second space and third dash. Any suitable timing devices may be used, but, as shown, they comprise rotary switches connected to a constant-speed motor-driven shaft by clutches M1, M2. The motor may be started up by an incoming signal, and allowance made for the motor to attain a constant speed, an alarm being given if the motor does not pick up speed. The dashes and also the spaces need not be of equal lengths and modifications for the reception of such signals are described. Operation by correct signals. The aerial and battery are connected up by switch W. On arrival of the first dash, receiving relay Sr operates Ar and Br, Dr pull up and lock. Br switches in the motor M over a circuit including resistance R which is short-circuited by a contact of the governor SG until the motor speeds up. Ar and Dr energize the electromagnetic clutches M1, M2 which respectively connect wipers N1, N<1>1 and N2 to the motor shaft. When the dash has persisted for the minimum tolerated period, N<1>1 reaches arc C4, Kr1 energizes, connects arc C13 of N2 to relay Gr, connects up Lr1 (short-circuited over C4) in series, and releases clutch M2, whereupon wiper N2 returns to normal. Lr1 Kr1 are the first pair of a relay chain which counts correct dashes. If the signal terminates within the tolerated period (N<1>1 still on C4), the relapse of Ar releases clutch M1 to restore N1, N<1>1 so that Lr1 pulls up in series with Kr1 transfers the circuit of C4 to the second pair Kr2, Lr2 of the chain and again connects up clutch M2 which remains operated for the duration of the complete signal. The circuit of clutch M1 is maintained open during restoration of N<1>1 to normal, by Er operated over N1. The second dash operates Ar which energizes clutch M1 and if the dash is acceptable, Lr2, Kr2 are operated similarly to Lrl, Kr1 The third dash then operates Lr3, Kr3 and Lr3 brings in the alarm ALD in parallel with Hr which locks and holds the alarm. The wiper N2 which has rotated continuously since the termination of the first dash reaches C13 after the termination of the 3rd dash if the signal is acceptable. Cr pulls up, locks and releases Br, Dr to disconnect the motor and Gr operates to release the counting chain. The circuit can only be fully restored to normal for the receipt of another signal by operating key RK.. Rejection of incorrect signals. A solitary short dash energizes Ar, Br, Dr, the motor is started and clutches M1, M2 operated as before, but at its termination Krl is not operated and clutch M2 not released. M1 is released and N1, N<1>1 return to normal. After about 13 seconds N2 reaches C13 to operate Cr which releases Br, Dr, the latter releasing immediately to de-energize clutch M2 and the former slowly to stop the motor. Cr remains locked until released by Ar on receipt of another signal. If a new signal arrives during the slow release of Br, the release of Cr restores the circuit of Br and the motor continues to rotate so that too frequent starts of the motor are avoided. If a dash is too long, wiper N<1>1 reaches C5 to operate Gr which locks up and releases the operated relays of the counting chain. Clutch M2, de-energized by Kr1 when N<1>1 reached C4, is again energized to drive N2 forward again. Clutch M1 is not de-energized, but wipers N1, N<1>1 are held with N<1>1 on C5 and the clutch slipping as will be described in a subsequent paragraph. If the signal stops before N2 reaches C13, the relapse of Ar releases clutch M1 and relay Gr, and wiper N2 proceeds to C13 with results as above. If wiper N2 has already reached C 13, Cr pulls up, but Br, Dr and Gr are held until the signal ceases. Incorrect signal immediately followed by a correct signal. At the end of an incorrect signal, wipers N1, N<1>1 are back to normal, but N2 is still rotating. If the first allowable dash terminates before N2 arrives at C13, the selector will operate just the same as if it were started by an allowable dash. If N2 reaches C13 during the dash, Cr operates, but Br, Dr remain operated by Ar and N2 remains on C13 with clutch M2 slipping. At the end of the dash, wiper N<1>1 reaches C4 to operate Kr1 which releases clutch M2 and relay CR and the circuit conditions are those normally present at the termination of a first dash. Relay Gr is slow and does not pull up although a circuit is completed by Krl. Allowance for starting period of motor. If an allowable signal arrives when the motor has already been started the time measured by wiper N<1>1 for the first dash will be shorter than if the signal had to start the motor. To correct this, the tolerance may be slightly extended or the operation of clutch M1 may be delayed by making it slow acting or by completing its circuit by a slow operating relay. Motor slow to pick up speed. As soon as the motor is started by Ar, Br a circuit is completed for slow-operating relay Pr over governor contacts 2 and if these contacts remain closed, Pr pulls up to bring in alarm ALD.. Construction of clutch driven switch, Figs. 5 and 6. The construction shown applies to the clutch M1 and wipers N1, N<1>1, Fig. 4, but a similar arrangement is used for M2, N2. A fixed shaft D carries an electromagnet E rotated through gearing F, G at constant speed. The shaft D also carries a rotatable armature H on the central boss of which is loosely mounted a plate K carrying the wipers N1, N<1>1 which wipe over contacts Hc, C4, C5 and Bc respectively. Plate K is pressed against armature H by a star shaped spring I and a spiral spring L tends to hold the wipers in the normal position with stop c on plate K engaged with fixed stop b. The tension of spring L may be varied by rotatably adjusting the shaft D. When rotating magnet E is energized it rotates armature H and plate K and if the energization is sufficiently protracted to bring stop a on the wiper plate K in contact with fixed stop b, slip occurs between plate K and the armature which continues to be rotated by the magnet. On de-energization of the magnet, spring L restores the armature H and plate K, but armature H still continues to rotate by inertia after reaching normal and prevents rebound of the plate K.