After these settings are made, it should be possible to reproduce
the proper meter indications at 0.01 and 10 mr/hr without any further
adjustment.
The instrument should then be calibrated over its full range by
obtaining the recorder current for several values of radiation and
plotting a curve which should match curve A shown in Figure 4.
If
there is a departure from linearity, compensate by readjusting the B
plus set control, R-29, slightly.
However, if this is done the switch
should be then turned to the SET position and R-30 readjusted to
froduoce a recorder current of 0.70 ma.
Should there be a marked non-
linearity in the calibration curve, it will be necessary to select new
amplifier tubes, V-1 and V-2 until a pair is found which will gve the
fequired characteristics.
To calibrate the high level detector, set the range switch to
position C and repeat the procedure for setting the photomultiplier,
tube gain control and the float control described above;
however,
use radiation values of 10 mr/hr and 10 r/hr to correspond to currents
of 0.200 and 0.740 ma respectively.
Selection of the proper
photomultiplier tube, VR tube (V-4) and gain control adjustment (R-19)
should bring the detector into proper calibration as shown by curve B
in Figure 4, without any further change of B plus or amplifier tubes.
20505
Buck-Out Circuit
Set the arm of K-34] at 1,850 ohms between it and ground as measured
by an ohmmeter.
The buck-out potentiometers are then adjusted
to
produce zero volts measured between the arm of switch S-1H and ground
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