Patent GB-238639-A (GB)
Title: Improvements in devices for measuring brief intervals of time
IPC: G01S1/72
Filed: 1924-06-02
Abstract: 238,639. Behm, A. June 2, 1924. Short-time movements. Devices for measuring short intervals of time, for example for acoustic depth measurement, operating as described in Specifications 164,011 and 183,490 comprise a spinning or oscillating disc which (1) is wholly or partially transparent or translucent including a transparent or translucent rim bearing a scale coacting with a stationary zero or (2) is opaque and arranged to reflect incident light illuminating the scale on the disc. The scale reading in each case being projected on to a matt surface. The appropriate part of the scale 8 on the disc 7 is projected by a lamp 10, condenser 11 and objective 13 on to a limited field 16 of a matt screen 15 bearing a zero mark 17. The disc is arrested by a brake 18 on the armature of a magnet 19, whilst energization of a second magnet 34 attracts a drum-shaped armature 33 on the arbor 32 of the disc whereby a stop 30 on the disc moves back and stresses a spring 31 so that on de-energization of magnet 34 the disc is set spinning and is later arrested on de-energization of magnet 19. Instead of magnet 34 and armature 33, a magnet 29, Fig. 4, may coact with an arcuate armature 27 on the disc which armature is supplemented by an arc 28 of non- magnetic material to form a complete ring. To dispense with an armature rigid with the disc, the impelling spring 31, Fig. 4a, and armature 39 thereton coact with magnet 40, which on energization stresses the spring 31, a stop 30 on the disc following the spring up by reason of the action of the recoil spring 42. In a modification of this form a ball of agate, glass, or precious or semi-precious stone on the disc co-operates with a ball seat of the same material on the spring 31. In the case of an oscillating disc 7, the latter after 360‹ of rotation may stress another spring which returns it in the reverse direction. The following features are also described; (3) the revolutions or oscillations of the disc may be counted on an appropriate counter, or indicated acoustically, or by means of a film strip fed step by step, or by means of a special transparent scale disc geared to the spinning; (4) the whole apparatus may be contained in an evacuated casing to diminish friction ; (5) the brake mechanism may include a three-armed member, each arm having a weight adjustable along it in order that the time of operation of the brake may be varied; or an eddy current brake may be used including an aluminium disc geared to the spinning disc; (6) by a suitable magnet member several spinning discs may be released simultaneously, and arrested thereafter individually in order that comparison may be made under the same conditions of temperature &c. Brake indicators, applications of.-Operatively connected to the brake 18, Fig. 3, by a bar 21 is a filter 22 which, on operation of the brake, intercepts the beam of light 12 so as to effect colouration of the illuminated field at 23. Alternatively, operation of the brake may be indicated by the extinction of a lamp. Electromagnets. - As the distance from the armature to the magnet, Fig. 10, is extremely small, any slight tilting of the armature would seriously affect the precision of the instrument and to avoid this there are three points of engagement 104, 105 on the armature, the upper contacts 104 being in series or in parallel with the magnet winding.