Patent GB-409690-A (GB)
Title: Improvements in or relating to signal formulating devices
IPC: G08B25/04
Filed: 1932-11-02
Abstract: 409,690. Fire, police, and like alarm systems. GAMEWELL CO., Linden Street, Newton Upper Falls, Massachusetts, U.S.A.- (Assignees of Beach, C. E. ; 23, Warwick Road, Brookline, Massachusetts, U.S.A.) Nov. 2, 1932, No. 30889. Convention date, Nov. 5, 1931. [Class 40 (i).] A non-interference code-wheel type transmitter is arranged to give earth return working in the event of faulty line conditions, the non- interference mechanism being ineffective during such emergency working. Under normal conditions the code is transmitted four times but the mechanism provides for a maximum of 23 revolutions of the code wheel when the line is in use by other transmitters. Normal operation. When the starting handle 33 is pulled, the plate 37 is swung in a clockwise direction removing arm 39 from notch 42 and dog 40 from the path of pin 44. The spring 1 starts the mechanism, the speed of rotation being controlled by escapement 24 (Fig. 6). Off-normal springs ON, which normally shortcircuit the transmitter, are opened to connect magnet MM in the loop circuit whilst contact arm 91 rides a skirt 100 of the code wheel, maintaining contacts PC closed. As the line is clear, magnet MM energizes and the armature extension 102 moves clear of the path of pin 106 (of arm 91). Pawl 108 rests on the ledge 107 of armature extension 103 holding arm 109 in its depressed position. The arm 91 cooperates with code-wheel 18 to transmit the appropriate code to the central station. As the contacts PC open, magnet MM is de-energized but its armature is prevented from falling by pin 106 which supports 102 during these periods as indicated in Fig. 16. The counting wheel 41 is mounted loosely on shaft 4 and makes a quarter of a revolution for each revolution of the code wheel. The code wheel is rotated four times, the skirt 100 being moved out of the path of 93, as indicated in Fig. 8, for each revolution after the first. After four rounds of the signal have been transmitted notch 42 again receives stop arm 39 thus allowing plate 37 to return to its normal position and move stop dog 40 into engagement with pin 44. The shunt switch ON is closed and pin 97 swings lever 122 and with it pawl 108 into the normal position. Non-interference arrangement. Should the line be engaged when the starting handle 33 is operated, the mechanism commences to function as before described. The skirt 100 is of sufficient size to ensure a break in the signal train being received whilst 100 is supporting 93 if another station be transmitting so that MM is de-energized and arm 103 no longer supports 108. The cam 113, which is rotated with shaft 17, removes its support from 109 which swings anticlockwise so that its end engages the pin 106 to hold arm 91 in its inoperative condition. The mechanism remains in this condition whilst 17 makes a revolution when skirt 100 again supports 93 and cam 113 lifts 109 into its normal position. If MM remains energized whilst the skirt is supporting 93, the code is then transmitted to line as described above but as 17 has already made one revolution, the code is sent three times only. If however the line is still engaged, MM again releases and the signal arm is looked in an inoperative position for a further revolution of 17. This cycle is repeated for each revolution of 17 until the line becomes free. After the first ineffective round of 17 as 109 is still in its blocking position the dog 129 engages pawl 48 which opens the clutch 46-48 (Fig. 14) so that 41 is not rotated. On each revolution of the gear 19 however the pin 44 steps wheel 152, the wheel being held by member 153 as indicated in Fig. 18. If the line should become clear, the clutch 48 is released by the movement of 109 and the counting wheel 41 again becomes effective to allow the signal to be transmitted three times as described above. If the line still remains busy however, the wheel 152 is rotated 12 steps and then 44 engages the long tooth 164 whilst the pawl 157 engages the teeth 172. The long tooth 164 is so shaped that 44 moves 152 less than one tooth so that when the pin and tooth disengage, 152 is dragged back, by spring 154 into its 12th step position. The wheel 47 is however moved one step. When 19 has made a further revolution the pin 44 again engages the long tooth 164 and 47 is moved a second step which moves 47 far enough to disengage 48 and 129 so that the clutch 46-48 is reclosed and on the next revolution of the shaft 17 the counting wheel 41 is moved a quarter of a revolution. If the line should now become free, only two code cycles are transmitted. If the line remains busy however the step-by-step movement of disc 47 is repeated twice and 46-48 is again closed to move 41 through its third quarter, the cycle being repeated again if the line is still busy to restore the mechanism to normal, no code transmission taking place. Emergency operation. If the line is faulty the switch EW (Fig. 21) is moved to the left which joins the two line wires to the positive pole of battery and earths the negative pole. When the transmitter moves off-normal under these conditions the magnet MM is not energized. The latch arm 109 rocks counterclockwise to block pin 106 and cam 113 lifts 114 into a position where 117 is latched over ledge 118 of pawl 108 (see Fig. 13). As MM is not energized, when the shaft 17 has completed a revolution the cam 113, in engaging the fluke 127 of arm 109, swings the arm clockwise and 114 moves with the arm, lifting arm 137 to allow contactor 78 to be swung into engagement with 73, 74 and 77. The dog 129 is moved out of engagement with pawl 48 to allow clutch 46-48 to re-engage on the next revolution of the signal wheel. The armature of magnet MM is held in attracted position by arm 137 so that the non-interference arrangement is in-operative and four signal cycles are transmitted over an earth return circuit. As indicated in Fig. 21 the magnet MM is shortcircuited when the emergency switch ES is closed and the code wheel is effective to open both line circuits. So long as the switch EW has been operated, the transmitter can effectively send signals on a broken or earthed loop or if the station is shorted as at X and Y. If the box is isolated by broken or earthed circuits at X and Y, the signal wheel is rotated 5 times only so that energy is retained in the spring to transmit signals if required after the circuit wires have been attended to. Arrangement using rectified alternating current. Fig. 22 indicates a current supply arrangement in which the battery of Fig. 21 is replaced by rectified alternating current. Normally signals from operated boxes are received on devices A and J unidirectional pulsating current being supplied by the rectifying bridge, but should a box change over to emergency working, the signals are received on device R the current supply being half wave rectified current. No emergency switch such as EW (Fig. 21) is required at the central station with this arrangement.