We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
LIGHT MODULATOR
243
Film Drum
Magnet Housing
Oil-Filled Wei (Damping Fluid)
Mirror Cemented to Suspension Ribbons
Condenser Lens
Fig. 53. Duddell oscillograph — optical system arrangement. This instrument has been familiar to electrical engineers for some 50 years. The electrical terminals are at the top of the ribbon. The ribbon is a continuous piece from top to bottom and back again; this results in opposite directions of current flow in the two parts when a potential is applied to the terminals. The current causes a twisting of the cemented mirror due to its reaction upon the strong and uniform magnetic field surrounding the ribbons. The ribbon and mirror assembly is immersed in a fluid such as mineral oil to effect mechanical damping.
Source impedance (must be resistive) : 600 ohms. Bias coil d.-c. resistance: 180 ohms ±10%. Sensitivity (modulation): +26 dbm±l db for 100% modulation at 1000 cycles. Bias current required: 25 to 30 ma. Frequency response (referred to 1000-cycle response) : ±0.5 db from 100 to 5000 cycles; ±1.0 db from 5000 to 9000 cycles. Distortion (at 100% modulation) : Total harmonic distortion not greater than 1.0%. Phasing : Upward deflection of the light image will be obtained with d.-c. applied to the modulation and bias winding of polarity indicated at the terminals. Important: Recorders other than those designed with the MI-10751 galvanometer as a companion item require changes in the input circuit before the deluxe galvanometer may be used.
' DAMPING LINE
Fig. 54. Dry galvanometer — cut-away view (RCA film recording galvanometer MI-10751).
magnetic field in which the conductor is located (Fig. 53). The light beam reflected from the mirror moves in accordance with the current applied to the conductor. Ordinarily, the conductor is stretched to a point not far below the elastic limit of the conductor strip ; a common conductor material is molybdenum. The magnetic field is customarily provided by a permanent magnet (e.g., Alnico 5). The mirror may be a first-surface square mirror 0.050 in. square. The assembly is immersed in oil for damping; the resonance frequency of the assembly is customarily about 10,000 cps. This type of galvanometer is the finest ever devised for obtaining freedom from disThe changes in temperature of the damping fluid cause undesirable changes
tortion.