International projectionist (July-Dec 1934)

10 INTERNATIONAL PROJECTIONIST December 1934 A c coMPOHf/vr /PscT/f/e// /%•? -5/f riro Gehc/ta ron /j'scr/F/c/p //r/iyy 1/zi/r, £/G/yr £/AT61 Note: Lower curves show wave shapes from single two and three-phase rectifier and from generator. Upper curves show A.C. component from each FIGURE 3 Illustrating how the three-phase, full-wave rectifier fills in the gaps in the current wave that exist when a single-phase rectifier is used suits were not attainable with singlephase rectifiers. Both the three-phase rectifiers and the motor-generators delivered satisfactory results. (6) To determine the change of light intensity for various values of current through the arc, the same optical sys per cent increase in the current. (7) Lamps of five different makes, designed for d-c. operation with Suprex carbons, were tested and compared on the basis of projected light. The same projector was used in all the tests, only the lamps being changed. The results tem and the same measuring instruments indicated that although the lamps all had were used throughout, and all tests were made with the shutter running. The results are therefore comparative, and are not computed in lumens per square foot (Fig. 4). Burning the 6 and 7-mm. combination at 42 amperes, the arc consumed 1290 watts and the maximum average light intensity was 54 units. At 45 amperes the arc consumed 1440 watts, and the light intensity was 65 units. Thus, an increase of 11 per cent in wattage afforded a 20 per cent light increase. Burning the same combination at 50 amperes, the arc consumed 1700 watts. and the maximum average light intensity was 80 units. Thus, an increase in wattage of 32 per cent gave an increase of 48 per cent in light. This over-all increase was thus accomplished with a 19 per cent increase in current, or a 32 per cent increase in wattage. (Fig. 5.) reflectors of different sizes and focal lengths, the projected light in every case was of practically the same intensity for the same arc current. Various Power Sources (8) In determining the efficiency and powerfactor of the various sources of arc current, the following were considered: (A) 110-volt direct current from power mains. (B) Motor-generator, 80-volt d-c. output. (C) (D) (E) ator. (F) (G) Motor-generator, 60-volt. Motor-generator, 40-volt. Motor-generator, double the case of the motor-generator), for a minimum load of 40 and a maximum of 65 amperes. The values of efficiency follow : A (110-v., d-c. mains) 27 to 36 per cent. B (m-g., 80 v.) 26 to 35 per cent. C (m-g., 60 v.) 40 to 45 per cent, at 40 to 55 amperes. D (m-g., 40 v.) 45 to 48 per cent, at 40 to 50 amperes. (The limited capacities of the motorgenerators in C and D did not permit testing them with the 60 to 65 ampere arc.) E (double generator, single-motor type) 45 per cent, at 45 to 50 amperes. (Not tested above 50 amperes, the rated capacity of the motor-generator.) F (single-phase rectifier) 48 to 55 per cent, at 40 to 50 amperes. (Capacity of rectifier, 50 amperes.) G (Three-phase rectifier) 61 to 72 per cent, at 40 to 60 amperes. (Although the rated capacity of the rectifier was 60 amperes, the efficiency at 65 amperes was 75 per cent.) The power-factor of the motor-generator sets tested ranged from 78 to 83 per cent. The power-factor of the singlephase rectifier ranged from 80 to 85 per cent; and of the three-phase rectifier from 85 to 90 per cent. (9) Examination of reflector mirrors in theatres in which Suprex carbons have been used for some time shows that there is continual pitting, resulting in a noticeable decrease in screen light. In order to maintain the screen illumination at its best, the mirrors should be replaced when noticeably pitted. Mirror Guard Approved There has been introduced recently a shield, or mirror guard, made with highquality optical glass and having the same curvature as the mirror it is intended to protect. This guard fits exactly the inside curve of the mirror and acts effectively as a guard against pitting. Various sizes of mirror guards have been tested by the Committee and found to occasion a negligible light loss. When the mirror guard itself becomes Single-phase rectifier. Three-phase rectifier. Measurements were made of the overall efficiency, or the proportion of direct When the 6.5 and 8-mm. trim was current delivered to the arc with respect pitted, it can be easily removed and reburned at 50 amperes, the arc consumed l0 tne current drawn from the supply placed with another, effecting a con1540 watts, and the maximum average line (including the ballast resistance, in siderable saving over the cost of a new light intensity was 70 units. At 55 amperes the arc consumed 1800 watts, and the average light intensity was 84 units. Thus an increase in arc wattage of 17 per cent provided an increase of 20 per cent in light. At 60 amperes the arc consumed 2100 watts, and the average light intensity was 100 units. Here an increase in arc wattage of 36 per cent resulted in an increase of 43 per cent in light. At 65 amperes the arc consumed 2435 watts, and the average light intensity was 115 units. Thus, with a total increase in wattage of 58 per cent the light was increased by 64 per cent. However, this represents a 30 FIGURE 4. Variation of light intensity with arc current 70 8 so 40 F/c S 6S 3„„C/I R30/ V 6-7 *1H C AflQt A/S 6 o 8 U/GHT 0 UN/ rs 10 O /2 0