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.
V3 and V4 are a stabilized amplifier of constant gain. V5 and V6 comprise a balanced vacuum-tube voltmeter. Line voltage changes are balanced out and will not affect the readings. This does not mean that the instrument should be used without a voltage regulating transformer, as changes in the supply for the light source will greatly affect the stability of reading.
The indicating meter Ml has special pole pieces to give the instrument an approximately linear scale with logarithmic input over a 10 to 1 range. The circuit is arranged in such a manner that with an increase in current, the coil of the meter moves into a magnetic field of lesser density. This arrangement prevents a runaway condition and makes for a better instrument. P3 is the 1.0 calibrating adjustment.
Figure 5 shows the frequency response of the amplifier section V3 and V4. This characteristic is caused by the tuned circuit in the cathode circuit of V3. The peak transmission corresponds to the frequency of the interrupter wheel in the light beam and eliminates
to a great extent errors in reading due to stray light reaching the photoelectric cell.
The filaments of all tubes are fed from a direct current source. The anode voltages on the photoelectric cell and of V2 are sufficiently low to eliminate any noise and nonlinearity due to gas present in the tubes.
Figure 6 shows the finished instrument. The unit is made to fit into a table or desk with the power unit to be mounted out of the way of the operator. All controls are located on top of the panel.
Upon completion, the unit was tested with several different lamps as light source. Reproducibility of readings was checked over a four-week period. The first two weeks the unit was checked each working day by the hour on the hour, allowing a 5-min warm-up period before making a reading. The instrument was shut off after each test. The latter two weeks the instrument was left on continuously.
The readings thus obtained were in all instances within 0.02 of the original
Fig. 6. Model 1503 A color densitometer. Frank Pt Herrnfeld; Color Densitometer
189