Then adjust R-30 until the recorder reads 0.70 ma.
When making any
calibration adjustments, tap the recorder tape in front of the pen
until the pen comes to its final reading.
2.3.2
“Top Hat" Detector Calibration
There are three mechanisms for obtaining the desired calibration
curve, these are:
A.
Adjustment of the gain of the photomultiplier tube to obtain
the proper slope.
B.
Adjustment of the bias control to set the low end of the
calibration curve.
C.
Adjustment of the amplifier plate voltage supply to bring the
amplifier into the logarithmic portion of its charucteristic.
The gain of the photomultiplier tubes is adjusted by selection of
the voltage regulator tubes, and setting of th potentiometers R-9 and
R-19.
1000 volt corona regulator tubes (V-3 and V-l,) should be used
as a first approximation to the proper value.
With the range switch
at position A, and the detector in a 10 mr/hr radiation field, adjust
the low level photomultiplier gain control, R-9, until the recorder
reads 0.82 ma.
Should it be impossible to reach this current, the
1000 voltage regulator tube, VR-4, should be replaced with one
regulating at a higher voltage.
0.01 ma and set the amplifier
Then reduce the radiation field to
grid bias control (float control)
R=-27 to produce a recorder indication of 0.275 ma.
(If the recorder
current cannot be brought down to this value the photomultiplier tube
has too high a noise level and should be replaced).
Check the
current at 10 mr/hr and if it has changed read just R-9,
Then check
the 0.01 mr/hr point end make any necessary adjustment with R-27.