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 TM 11-6665-232-40
increases. This drives more current through the
the aid of the induced voltage from windings
meter circuit and causes the meter to deflect
T1-4 and T1-1 into the feedback winding. Q1
and register in the "CHECK BAND" marked on
stays in saturation until current in T1-4 and
the meter face.
T1-1 stops changing. At this time, the induce
(c) When S2 is set to operate, the ioniza-
voltage in the feedback winding reverses to
t i o n chamber walls are connected through
bring Q1 into cutoff,
b. The process of Q1 going from cutoff to sat-
P1/J1-F and S2A contacts 5 and 3 to +2.8 volts
from the converter. Also, the control grid of V1
uration, to cutoff, repeats providing changing
is connected through R1, P1/J1 pin H and S2B
current in the primary winding of T1, pins 4 to 1.
contacts 9 and 11 to the common negative of the
Because of step-up transformer action the volt-
converter. As a result, the ionization chamber
age induced in the secondary winding of T1 (pins
wall is made positive with respect to the elec-
2 to 3) is much higher than the voltage in the
trode in the control grid circuit of V1. When
primary.
gamma
c. Diode CR1 is used to rectify the stepped-up
strikes
the
ionization
voltage from the secondary of T1. Capacitor C2
chamber, current is caused to flow through R1
and the electrode to the ionization chamber
filters the rectified stepped-up voltage and the
wall, and a positive voltage is produced in the
process of converting a low voltage dc to a
higher voltage dc is complete.
control grid circuit of V1.
d. The converter module also contains an
2-6. Converter
integrated circuit (IC) voltage regulator and a
voltage divider The IC is a small sized, sealed
The power supply for the single battery
component which contains transistors, diodes,
radiacmeter is a dc to dc converter. The input to
and other circuit elements to provide highly
the converter is the battery voltage of 1.5 volts
regulated and stable dc output voltages. on the
dc. The converter's highest output voltage is
schematic the IC is labeled VR1. The voltage
+13.2 volts dc. This voltage increase is brought
divider consists of resistors R4, R7 and R6. The
about by taking the low input voltage and;
voltage divider provides the proper range of volt-
changing it into an ac voltage; applying the ac
ages for the operation of R5, the zero set poten-
voltage to a step-up transformer; rectifying the
tiometer. VR1 produces 2 regulated dc output
stepped-up voltage; filtering and regulating the
voltages, +2.8 volts and +1.4 volts. The +2.8 vdc
stepped-up (converted) voltages.
output is connected to pin 5 of the converter and
a. When S1 is set to ON, battery voltage is
is used to bias the ionization chamber during
applied to a free running oscillator circuit con-
operation of the radiacmeter. The other output,
sisting of R13, R14, C1, Q1 and T1. Resistors R13
+ 1.4 volts, is only used when the radiacmeter
and R14 form a voltage divider network to sup-
circuits are checked (para 2-5b above).
ply bias current. to Q1 through feedback wind-
ings T1-6 and T1-5. Q1 goes into saturation with
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