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(4) LIGHT SOURCES
(S)
Various types of light sources are shown in attached
Price List 18-316 all of which, except the type L, can be
used with the Type RX Photo-troller. In selecting the light
source care must be taken that the minimum illumination on
the photo-tube must not exceed the values given in fig. 2.
In this figure are shown different scales for the
maximum illumination for different percentage changes in
a-c line voltage. Using, for example, the basic 2% curve
it is seen that if the maximum illumination is 30 foot
candles, the minimum illumination must not exceed 15 foot
candles. If, however, the maximum line voltage variation
is 20 per cent and the maximum illumination is 30 foot candles
at maximum a-c voltage, then the minimum illumination
10 foot candles is found by following the circle from A to
B, then to C and D.
By using tho curves in fig. 2 in combination with the
light source curves in fig. 7 of Price List 18-316, the percentage
reduction in light required can be determined.
x8.mp1
Light Source Type F.
Voltage Variations 10%.
Operating Distance 10 feet.
From fig. 7 Price List 18-316 is found: 17 F.C.
From fig. 2 ; 17 F.C. at 10% voltage variation gives
7.5 F.C. minimum illumination.
Consequently: Illumination must be reduced from
17 F. C. to 7.5 J:il. C. or 56%.
I t
PRINCIPLE OF OPERATION
The schematic diagram, for the type RX photo-troller
is shown in fig. 3. The photo-troller is equipped with a
type WL-629 Thyratron tube which is controlled by a type
WL-735 phototube. The WL-629 tube is a gasf'i11ed discharge
tube consisting of an anode connected to lS in fig. 3, a
heater winding connected to leads 8 and 10, a cathode con­
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nected to Lead 8J and a control grid connected to the S
MEG. resistor. The characteristics of the WL-629 tube are
such that when the grid has a negative potential exceeding
approximately 6 volts relative to the cathode the tube does n
not become ionized, and no current is conducted through the
tube. If the grid potential is made more positive, the
tube breaks down,and conducts rectified current through
relay coil I during the half cycles when lead 7 is positive
in relation to lead 8.
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