Patent GB-710351-A (GB)
Title: Improvements in or relating to devices for testing electrical watt-hour meters or similar rotating systems
IPC: G01R35/04
Filed: 1951-05-24
Abstract: 710,351. Photo-electric apparatus for testing electrical watt-hour meters or similar rotating systems. SANGAMO WESTON, Ltd. May 24, 1951 [May 26, 1950], No. 12209/51. Class 40 (3). [Also in Groups XXXV and XXXVI] Watt-hour meters or similar rotating systems are tested against a rotating standard with apparatus which incorporates photo-electric cells and produces automatically a printed record of the calibration and test performance of each meter. Full load testing.-In Fig. 1 the slotted disc standard meter S coacts with light source 26 and photo-cell 27 with associated amplifier 27 to energize a stroboscopic lamp 35 and field winding 29 belonging to a synchronous motor 14. The meter T under test has a disc 30 with radial lines 31 equal in number to the peripheral slots 25 in the disc 24 of the standard S. The synchronous motor 14 drives a cylinder 15 at a speed which is an integral number of times greater than the speed of the disc 24. The meter T is adjusted until the speed of its disc 30 with the aid of the stroboscopic lamp 35 appears the same as the speed of the disc 24 in the standard meter S. The cylinder 15 is formed with a helical ridge 16 and a paper tape 17 is driven transversely and a typewriter ribbon 18 is driven longitudinally with respect to the axis of the cylinder 15. As the disc 30 of the meter T rotates the anti-creep hole 32 therein permits light from a source 33 to activate a photo-cell 34 so that once per revolution of the disc 30 the output of the photo-cell 34 through an amplifier and trigger circuit 23 operates a solenoid 22 to cause momentarily a printing bar 21 to press downwards the ribbon 18 and paper tape 17 on to the helical ridge 16 and thus form a mark d on the tape 17, Fig. 2 The dots d will slope as at A if the meter T is slow and as at B if it is fast and in the case of zero error there is zero slope as at C. The tane or chart 17 is scaled so that the distance across the chart between successive dots d indicates directly the error per cent. The scaling and recording on the chart 17 with respect to equipment design and operation is fully treated mathematically in the Specification. Light load testing (10 per cent full load).- The standard S continues to rotate at full load speed as provided for in the phantom load arrangements, Fig. 6 (see below), and the svnchronous motor 14 which may be a different one designated for th's test (see below) drives the cylinder 15 at 10 per cent of the speed it was driven for the full load test. The chart 17 as calibrated for full load is therefore correctly calibrated also for 10 per cent full load testing Tn differentiate the two tests on the chart 17 the 10 ner cent full load test performance is distinguished by introducing a series of pulses into the triggering circuit 23 which appear on the chart 17. Synchronous motor equipment.-Two arrangements of single-phase synchronous motor pairs are illustrated, one of these motors being allocated to full load and the other to light load testing. According to one, Fig. 3 (not shown), the two synchronous motors are both directly coupled to the drive shaft 13 with the light load motor having ten times the number of pole pairs provided in the full load motor. In the other illustrated arrangement, Fig. 4 (not shown), both motors have the same pole pairs and the light load motor drives the shaft 13 through 10/1 reduction gearing. In this arrangement when the full load motor is energized the rotor of the light load motor remains inert through operation of a centrifugal clutch device. The amplifier 28 may be provided with phase-splitters whereby polyphase synchronous motors may be employed. The use of a single motor for full and light load testing is envisaged, this one motor being fed with A.C. at selected frequencies tapped from a multi-vibrator system thus to drive shaft 13 at the different speeds. Phantom load and motor selection arrangements.-In Fig. 6 with the rotary cam switch RS in the position shown full load current traverses the standard and test meter current coils SC, TC via closed switch contacts C5, C6 and current transformer 108 whose secondarv 111 is short-circuited by closed switch contact C2. Also the full load motor 14A is energized via closed C7 contacts. To produce light load test requirements the switch RS is given a half-turn to open C2, C5, C6 and C7 and close C1, C3, C4 and C8. Under this condition the light load motor 14B is energized and the current transformer secondary 111 via closed contacts C3, C4 supplies 10 per cent full load current through the test meter current coil TC. Full load current is maintained through the standard meter current coil SC via closed C1. Miscellaneous details and modifications.-Two meters may be tested simultaneously against a single standard with one test meter operating at full load and the other at light load and the standard operating at full load speed. In this modification the recording and printing mechanism is duplicated with two motors operating simultaneously and each driving a corresponding marker cylinder. A light chopper may be used instead of the stroboscopic lamp 35. Tests at full load 0.5 p.f. may be performed utilizing the full load motor and the same chart scale. Combs with appropriate apertures may be disposed above and below one or both the meter discs 24, 30 such as to cause the light to pass through the . disc apertures 25, 32 in parallel rays.