Patent GB-569940-A (GB)
Title: Methods of and apparatus for testing and calibrating meters having a continuously rotating element such as electric energy meters
IPC: G01R35/04
Filed: 1942-11-13
Abstract: 569,940. Stroboscopic apparatus. KINGSTON-UPON-HULL, CORPORATION OF THE CITY AND COUNTY BOROUGH OF, and MELL, R. E. Nov. 13, 1942, No. 16049. [Class 97 (i)] [Also in Groups XIX, XXVI and XXXVI] A meter is compared stroboscopically with a substandard meter by means of a rotating viewing device having a series of light apertures therein and driven in synchronism with the rotating element of the substandard meter, which is connected in common with the meter under test. The substandard meter 7, Fig. 1, is provided with a disc 8 having a series of slots, apertures or serrations located between a light source 9 and a photoelectric cell 10. The impulses produced are applied through an amplifier 11 to a synchronous motor 12, which is thus driven in synchronism with the disc 8. On the shaft of this motor is a viewing device comprising a disc 13 having one or more series of apertures through which the disc 14 of the meter 6 under test is examined. The disc 14 is provided with a series of spaced marking 15 from which the stroboscopic image is obtained. The voltage circuits of meters 6, 7 are connected to one phase of a three-phase supply 16. A change-over switch 17 enables the voltage circuits to be fed from a different phase from that feeding the current coils, for testing at 0.5 power factor. The current coil of the meter 6 is fed through the lapper primary coil of a multi-range precision current transformer 18, the secondary coil of which is connected to the current coil of the substandard meter 7. A number of resistances 19 are connected to the tappings to feed different currents to the meter 6, the ratio of the transformer 18 being such as to maintain constant current in the circuit of the meter 7 irrespective of what known fraction of that current is being fed to the meter 6. To permit testing at full and low load values the disc 13 either has two series of apertures or a variable speed drive. A modified viewing device is shown in Fig. 2 and comprises a viewing head 20 containing a light hollow cylinder 21 rotatable on a horizontal axis provided with one or more pairs of oppositely disposed slots through which the meter disc 14 is examined. The cylinder 21 is driven from a synchronous motor 12 through a driving shaft 24, bevel gearing 25, 26, and a shaft 27 on which are mounted two gear-wheels 28, 29 of different sizes. The cylinder 21 carries two gear-wheels 30, 31 and is mounted in a frame 32 slidable by means of projections 33' so that either the gear-wheels 28, 30 or the gear-wheels 29, 31 may be brought into engagement, giving two gear ratios suitable for low or full load rests. The viewing head 20 is removably mounted on a pillar 23 and may be exchanged for others of different gear ratios. An indicating hand may be driven by the synchronous motor 12 and a second hand may be provided for counting the revolutions of the first. Stop and start mechanism is provided so that the number of revolutions of the disc of the meter under test-may be compared with those of the substandard meter in the same time. A booster transformer may be provided in the voltage circuit of the meter under test, the controlling handle being calibrated in percentages fast or slow and having a spring to return to zero boost position. The stroboscopic image may be projected on a translucent screen by means of a lens. The invention is also applicable to the testing of other meters such as fluid-flow meters. Specification 569,941. is referred to.