Patent GB-682863-A (GB)
Title: Apparatus for testing the speed of rotating bodies
Inventor: MELL RAYMOND EDGAR
IPC: G01P3/40
Filed: 1949-05-25
Abstract: 682,863. Stroboscopes. METROPOLITANVICKERS ELECTRICAL CO., Ltd. May 25, 1949, No. 13999/49. Addition to 649,341. Class 97 (i). [Also in Groups XIX and XXXVI] An optical apparatus for testing the speed of marked rotating bodies and applied to electric energy discs, includes a sub-standard meter S, Fig. 1, energized by a constant load, and means 88 for supplying selectable desired loads to a meter M under test, the means 88 for selecting the desired loads for the meter M being coupled to means for controlling the speed of an optical refractor device 15 driven from the substandard meter S, the optical refractor being in a light path between the disc of the meter M and a viewing screen such that at any load setting a stationary stroboscopic image indicates correct adjustment of the meter. Instead of using a single refractor device 15, a plurality of refractors may be employed such as are indicated by the references 81, 82 ... 85, in Fig. 2, each rotating at a different speed and arranged such that the means 88 for selecting the desired loads for the meter M also brings the corresponding refractor into the light path between the disc of the meter M and the viewing screen. At any load setting, a stationary stroboscopic image again indicates that the meter is correctly adjusted. Each refractor comprises a pair of crossed optical flats 8 and shutter elements 12 covering the end faces thereof. In Fig. 1, the secondary side of a transformer T is tapped, as shown, at a number of points 77, 78, resistances R being inserted between these tapping points and the windings. The current coil 71 of the meter M under test is connected in the secondary side of the transformer T such that by electrically connecting together any two opposed tapping points 77, 78 the current passing through the coil 71 of the meter M bears a known relationship to the constant value of the current in the coil 171 of the sub-standard meter S. The selected opposed tapping points 77, 78, supplying fractional and multiple values of the load applied to the meter S, are connected to a number of opposed contacts 87 over which a pivoted arm 88 is movable to shortcircuit in turn the said opposed contacts 77, 78 and so vary the current in the coil 71 of the meter M. As the disc 6 of the meter M rotates, the markings on the disc 6 are viewed through an optical refractor 15 rotated by a synchronous motor 18, the speed of which is controlled by a photo-electric cell 76 below the disc 61 of the sub-standard meter S, the disc 61 being slotted so as to allow light pulses from a source 114 above the disc 6<SP>1</SP> to reach the cell 76. Between the synchronous motor 18 and the refractor 15 are a number of gears chosen to conform with the selected tapping-points 77, 78, the actual gears used being controlled by means 93 linked to the arm 88. Thus, if the arm 88 is moved to shortcircuit any pair of opposed contacts 87 to vary the current in the coil 71 and hence the speed of the disc 6, the said gears are automatically adjusted to rotate the refractor device 15 at the appropriate speed. If the meter M is reading correctly the marks on the disc 6 will appear to be stationary when viewed through the optical refractor 15. Any error in the.speed of the disc 6 will cause the marks to appear to drift in one direction or the other. Means 17 are provided to impart an additional or less rotary movement to the optical refractor 15 when operating at low speeds, in order that the meter M may be tested for cyclic variations. In an alternative arrangement, the arm 88 may be linked to the knob 16 of the apparatus described in the parent Specification. The alternative arrangement in Fig. 2 shows a rotatable turret carrying the plurality of optical refractors 81 to 85, each refractor rotating at a different speed. The turret is connected to the arm 88 by means 93 such that for any load selected for the meter M, the arm 88 automatically brings the appropriate optical refractor into the line of sight between the operator and the disc 6. The bevel wheel 110 of a differential device 57 is adapted to be rotated by a toothed ring 113 actuated by a flexible cable 63 from the light-load control device 17, Fig. 1. By this means additional rotary movement can be added to or subtracted from the optical refractors when operating at low speeds for testing the meter M for cyclic variations. The voltage coils 72 and 172, Fig. 1, are fed from two phases of a three-phase supply P, the phase wires being exchangeable by a switch 73 to permit load tests at unity and 0.5 power factor. Specification 569,940 also is referred to.