Patent GB-336996-A (GB)
Title: Improvements in or relating to fire alarm apparatus
IPC: G08B25/12
Filed: 1929-07-23
Abstract: 336,996. Automatic Telephone Manufacturing Co., Ltd., and Burns, G. A. July 23, 1929. Fire-alarm systems and apparatus.-In a firealarm system employing boxes adapted to be connected in series in a loop circuit and when operated to transmit characteristic impulses, if at the instant a box is set in operation the loop is already open a member controlling the impulse sending is moved to one or other of two positions according to whether the loop is or is not closed during a short test period. In the construction shown, when the box is set in operation by the usual handle, an arm 10 bears against a lever 11, whereby a pin 13 is moved away from a pin 14 curved by a governor wheel 15. The mechanism then runs down under the influence of a main spring on the shaft 16 of a driving wheel 17 adapted to drive through gearing a code wheel 19. Operation at a box which is pulled under normal conditions. The. wheel 17 is provided with a rim 22 adapted to raise a lever 23 whereby lever 11 is operated to maintain the pin 13 out of engagement with the pin 14. The box has two sets of springs 26, 27 normally held in the positions shown by a lever 28, the set 26 shunting the line coils 70 and the impulsing springs (not shown) which are held closed by a buffer 33 on a lever 34. The set 27 is adapted when closed to earth the centre point of the impulsing springs. When the wheel 17 moves from its normal position a butterfly cam 32 moves to allow a projection on the lever 28 to drop on to a part 31 of the cam so that the springs 26 open. Current then flows through the coils 70 so that armature 35 is attracted and a pin 37 thereon enters a groove 38 in a lever 39. The mechanism runs in this condition for a short test period which can be varied by adjustment of the position of the cam 32. At the end of this period a recess in a cam wheel 41 secured to the shaft of the code wheel 19 comes opposite a projection on a lever 42 allowing the latter to drop so that its upper end is below a projection on the lever 34. Immediately afterwards a point 45 on the cam 32 moves past a projection on the lever 28 allowing the earthing springs 27 to close. Also a projection on a cam 49 secured to the cam 41 engages a projection on a lever 50 which is thus lifted clear of a notch in a plate 51, so that the latter moves downwardly carrying with it a plate 52. A pin 54 on the plate 51 is therefore withdrawn from supporting the lever 34, so that the latter now rests, on the end of the lever 42. A further slight rotation of the code wheel shaft carries the point 48 of the cam wheel 41 to raise the lever 42 thereby throwing the lever 34 into engagement with the teeth on the code wheel. The mechanism then continues to run while the code wheel makes three complete revolutions. At the end of the third train of impulses the point 56 on the opposite wing of the cam 32 engages'the projection on the lever 28 to close the springs 26 and open the springs 27. Also a pin 57 on the cam 32 engages the end of the plate 51 to allow the lever 50 to drop into contact with the cam 49 and hold the plate 51 in its normal position, after its disengagement from the pin 57. Plate 52 is at the same time raised to a position opposite the pin 37 thereby preventing release of the armature 35 due to the short-circuiting of the coils 70. The pin 54 re-sets the impulsing lever 34. The mechanism continues to rotate until the projection on lever 23 falls into the slot between the halves of the rim 22 on the wheel 17. The movement of lever 23 permits, the trip lever 11 to assume its normal position placing the stop pin 13 in the path of the pin 14. Operation at a pulled box when another box is already sending. During the test period the line is opened by impulses from the box already calling, so that the coils 70 are de-energized and the pin 37 on armature 35 engages the end of plate 52. The lever 39, through gravity, is turned about its pivot 44 so that the tongue 59 engages the pin 37 until the line is closed whereupon the armature 35 is again attached and the pin 37 moves to the left allowing a further movement of the lever 39. Towards the end of the test period plate 51 falls, allowing the plate 52 to move away from the path of pin 37 so that on the next break in the line circuit the release of the armature 35 results in the pin 37 moving to the right extremity of a groove 62 in the lever 39. The armature is then out of magnetic influence of the coils 70 and the pin 37 has moved far enough to support the lever 34 clear of the teeth of the code wheel. When now the lever 28 drops on passing the point 45 in the cam 32 a buffer 46 thereon engages a groove 61 whereby the earthing springs 27 are kept open. The mechanism continues to run without transmitting impulses or interfering with the line circuit. On the completion of the third revolution of the code wheel the lever 28 is re-operated to restore the springs 26, 27 to normal, and the pin 57 on the cam 32 re-sets the plate 51 but the plate 52 which is flexibly connected to the plate 51 remains in position under the pin 37. When the projection on lever 23 comes opposite the slot between the rims 22, the lever commencing to fall, causes the notch 63 to engage the pin 64 on the armature 35, thereby moving the armature slightly so that the lower face 65 is engaged by a pin 66 on the wheel 15, and the armature is mechanically restored up to the coils 70, the pin 37 being moved out of the notch 63 and the lever drops to the notch 67, restoring the lever 39 to normal by striking against the pin 58. The mechanism now commences to send its characteristic code in the normal manner. Operation when line is disconnected. The box is tripped by movement of the lever 11, but the armature 35 is released to allow the pin 37 to move out of the groove 38 and rest against the plate 52. The lever 39 falls until the tongue 59 comes into contact with the pin 37. When the point 45 on the cam 32 moves away from the lever 28 the buffer 46 falls into the groove 68 on the lever 39, so that springs 27 close, to earth the centre point of the impulse springs whereby one of the coils 70 is energized by way of earth from the battery at the central station and the armature 35 is operated. The box is subsequently operated in the normal manner except that the lever 39 is re-set in the manner previously described in the case where another box is already sending.