Patent GB-381341-A (GB)
Title: Improvements in and relating to accelerometers
IPC: G01P1/12
Filed: 1931-10-13
Abstract: 381,341. Electric counter for excess accelerations. CAMBRIDGE INSTRUMENT CO., Ltd., MASON, C. C., and STALLAN, W. J., Chesterton Road, Cambridge. Oct. 13, 1931, No. 28478. [Classes 106 (i) and 106 (iii).] Apparatus for registering infractions of a predetermined acceleration particularly for use with aeroplanes, bridges and other structures comprises a weight 1 connected by flat springs 2 to a frame 3 and having a projection 5 into a concave recess in which projects the convex head of a micrometer screw 4 threaded through part of the frame 3. The springs 2 can thus be stressed by rotating the micrometer screw 4, a graduated head 6 on which in conjunction with the index 30 shows the degree of stressing. A contact 8 is carried by a spring 11 insulated from the screw 4 and a contact 7 is carried by a spring 9 adjustable by the milled headed screw 10. The contact 8 is normally held out of engagement with the contact 7 by a push rod 12 resting upon a recess in the concave part of the projection 5, passing freely through a bore in the screw 4 and bearing with an electrically insulated tip 13 against the under surface of the spring 11. The contacts 7, 8 are in series with a battery 21 and coils 19, 20 of an electromagnet having shaped polepieces 17, 18 and an armature 14, pivoted on pin 15 and controlled by the hair spring 16 so as to normally lie obliquely between the polepieces 17, 18 as shown in the drawing. The armature has an eccentric stud 22 balanced by the weight 23 and engaged by the forked end of the lever 24 pivoted on pin 25 and balanced by the weight 26. A ratchet wheel 27 is pivoted on the pin 25, engages with the ncn-return pawl 28 and is operated by the pawl 29 on the lever 24. The screw 4 is turned by the head 6 to stress the springs 2 so that a predetermined minimum upward acceleration of the framework 3 is necessary for the screw 4 to leave the weight 1 and allow the push rod 12 to fall to bring the contacts 7, 8 together to energize the coils 19, 20 of the electromagnet and thereby rotate the armature 14 through about 60‹ and cause the pawl 29 to pass from one tooth to the next of the ratchet wheel 27. On the acceleration falling below the predetermined minimum value the weight 1 and screw 4 again come into contact and the contacts 7, 8 are broken causing the de-energization of the coils 19, 20 and the rotation of the armature 14 to normal position under the action of the hair spring 26 thus entailing the turning of the ratchet wheel 27 bv one tooth in anticlockwise direction through the pawl 29. A known counter train is actuated from the ratchet wheel 27. The interval between the making and breaking of the contacts 7, 8 must be sufficient to permit of the full stroke of the armature 14 if the ratchet wheel 27 is to be actuated. Hence by making the period of vibration of the armature 14 and hair spring 16 comparatively long, say up to one-fifth of a second, and by making the period of vibration of the spring-controlled weight 1 very short only accelerations of the required magnitude and of a definite duration will cause the ratchet wheel 27 to be actuated. By this means the effect of parasitic connections and disconnections of the contacts 7, 8 due for example to engine vibrations in the case of aeroplanes may be avoided even when superposed upon accelerations which it is desired to register. A number of the instruments described can be carried on the same machine but set to count at different minimum accelerations.