F. H. Richardson's bluebook of projection (1935)

Record Details:

Title:
F. H. Richardson's bluebook of projection
Date:
1935
Publisher:
New York : Quigley Publishing Company, Inc.
Volume:
F. H. Richardson's bluebook of projection
Leaf #:
00068
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Media History Digital Library
Sponsor:
{"Media History Digital Library","Jeff Joseph"}
Coordinator:
Media History Digital Library
Description:
Date Added:
March 21, 2024
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50 RICHARDSON'S BLUEBOOK OF PROJECTION (70) As the carbons burn away, increasing the arc length, the voltage drop in the arc stream is increased, tending to reduce current flow. This in turn operates to decrease the voltage drop through the ballast resistance, and thus the voltage applied to the arc is raised to meet the requirement of an increased arc length and again a stabilizing effect is set up. To illustrate this action by specific example, assumea 30 ampere, 55 volt arc operating from a 1 15 volt circuit. A ballast resistance of two ohms will absorb the difference of (110 — 55) 55 volts between the arc and line voltage Should the current rise above 30 amperes, or fall below, the voltage absorbed in the ballast resistance will rise or fall proportionately, raising or lowering the voltage applied to the arc, as previously explained. Ihese changes are shown in the following table : TABLE I. . Arc Current Amperes Change in Arc Current Volts Absorbed in 2 Ohm Ballast Volts Applied at Arc % Change in Volts at Arc Rising Arc Current 3.3% 6.7 16.7 3.6 7.3 18.2 Falling Arc Current 3.3% 6.7 16.7 3.6 7.3 18.2 It is evident from this table that the effect of the ballast resistance is to restore the arc condition to normal and thereby maintain stable operation.