Patent GB-183490-A (GB)
IPC: G04F8/00
Filed: 1922-07-24
Abstract: 183,490. Behm, A. July 23, 1921, [Convention date]. Short time movements. -A timing device, particularly for depth-soundiug from aircraft or the like, is of the type in which a measurement is made of the angular movement of a rotating flyweight. Means are provided (a) for progressively braking the rotation, in order to secure a more open scale for the shorter intervals to be! measured, and (b) for permitting a plurality of revolutions to occur and to be counted, when the time-interval to be measured is a long one. The spring 82, Fig. 1, engages a pin 35 on the fly-wheel 18 and sets the latter rotating as soon as the detent 25 is released by the spring 27, on the de-energization of the magnet 28. As soon as the rotation has begun, the magnet 34 is de-energized and the spring 33 swings the spring 32 out of the way. The rotation is eventually stopped by the brake 19, and the fly-weight 18 is then zeroized by the electromagnet 22 acting on a semicylindrical armature 21 to which is joined a semi-cylinder 23 of vulcanite for preventing air-losses. Finally, the spring 32 is stressed, ready for the next measurement, by energizing the electromagnet 34. In a modification, the detent 25 is omitted, and the fly-weight carries an eccentric armature which can be drawn up against the pole-piece of an electromagnet in order to stress the spring 32. Rotation is in this case started by de-energizing the electromagnet, which is thereupon swung out of the way. The means for progressively retarding the rotation may comprise, when only part of a revolution is to occur, a permanent magnet 41 opposite the poles of which is cut a tapered slot 43, so that eddy-currents of increasing strength are set up as the pointed end 43a of the slot approaches the magnet poles. In a modification, a disc 44, Fig. 6, may move in a tube 45, Fig. 7, having a tapering slot 45<a>, so that increasing air-resistance is offered to the rotation as this progresses. In another modification, for use where a number of revolutions is to occur, a vane pivoted near the edge of the fly-weight 18 gradually moves out radially so as to set up the required increase of airresistance. In this case the revolutions may be counted by a ratchet-wheel moved step-by-step hv a pin rotating with the fly-weight, or by an electromagnet energized at each rotation. Or, as shown in Fig. 12, the ratchet-wheel 59 is rotated one step by the pawl 55 every time the magnet 53 is energized, that is, every time a beam of light 51, rotating with the fly-weight 18, falls on a selenium cell 52. The counter may be read direct from a window, or a series of contacts 66 corresponding to the various positions of the counter may be connected to separate sliprings with brushes 67, so as to co-operate with the brush 68 in closing selectively a set of circuits 67<a>. Each circuit when closed may effect the movement of a light-filter into the path of a beam which illuminates the scale, the latter comprising a series of concentric divisions so coloured that only the appropriate one is visible when illuminated through the filter. The arrangement for releasing the brake 19, Figs. 1 and 15, may comprise a microphone circuit 70 which, on receipt of a sound, acts through a transformer 77 on the winding 74 of a magnet, causing the brake 19 to be released and to break its own hold-on circuit at 72. In modifications, the winding 74 may be omitted, the transformer secondary being included in the circuit 75; or the transformer itself may also be omitted, the microphone being inserted directly in the circuit 75.