Single Battery Radiacmeters

11-6665-232-40

ionization chamber. The collector electrode of

contacts 5 and 4 of S2A, and connectors P1-H

the ionization chamber connects to pin 11, S2

and J1-H, and no difference of potential exists

through R1 and J1/P1 pin H. Pin 9 of switch S2

between the ionization chamber and the control

connects to the common line (ground). Pin 10 of

grid of V1. At the same time, batteries BT-1 and

switch S2 connects to the converter, to complete

BT-2 are switched out of the circuit through

the bias circuit.

connectors J1-H and P1-H, contacts 11 and 10 of

b. Meter Circuit.

S2B, and resistors R6, R7, and R5. As a result,

(1) Voltage is developed across grid resistor

the bias is removed from the control grid circuit

R 1 of cathode follower V1 by current flow

of V1, V1 conducts more heavily, and meter M1

through the ionization chamber. An increase in

provides an indication in the CHECK band on

this voltage increases current flow through

the scale.

V1. There is a similar increase in the cathode

(3) When S2 is set to OPERATE (center pos-

voltage as current flow through the cathode re-

i t i o n ) , batteries BT-1 and BT-2 are series-

sistor R2 (contained in the converter) also in-

connected between the ionization chamber and

creases. Meter M1 is connected between the

the control grid circuit of V1 through connectors

cathode V1 and a voltage divider composed of

J1-F and P1-F, contacts 5 and 3 of S2A, and

R4, R5, R7, and R6. As the voltage on the

contacts 9 and 11 of S2B, and connectors P1-H

cathode goes up, the voltage across the meter

and J1-H. As a result, the ionization chamber

g o e s up and results in a meter deflection.

wall is made positive with respect to the elec-

trode in the control grid circuit of V1. When

Gamma radiation does rates are then read di-

rect from the meter scale. Resistor R3 is used to

radiation

the

ionization

gamma

strikes

calibrate the radiacmeter.

chamber, current is caused to flow through R1

(2) Zero control R5/S1 consists of switch S1,

and the electrode to the ionization chamber

wall, and a positive voltage is produced in the

a two pole, two-position switch, and potentiome-

control grid circuit of V1. Bias for the control

ter R5 mounted on a common shaft. When S1 is

grid of V1 is provided from BT-2 through con-

set to ON, the battery voltage is applied to the

filament of V1, and to the converter. The conver-

tacts 9 and 11 of S2B, connectors P1-H and

J1-H, and R1.

ter produces the regulated voltages required for

d. Instrument Light. The instrument light

the operation of the circuit of the radiacmeter.

(not shown) is attached to the meter of those

Potentiometer R5 is used to balance the meter

radiacmeters that do not contain a radioactive

circuit and produce the same potential at its

dial. The instrument light is used to light the

wiper as is present at the junction of V1/R2.

meter dial during low light-level conditions. The

When these two voltages are equal, the meter

instrument light contains a 1.34-volt battery

circuit is balanced and the radiacmeter zeroed.

When switch S1 is set to OFF, it shorts meter M1

(BT-7), a No. 331 lamp (DS1), a battery/lamp clip

ring, and a spring-loaded switch connected in

and dampens the pointer movement when the

series. When the lamp switch is pressed, the cir-

radiacmeter is not in use.

cuit is completed and the lamp lights.

(3) Function switch S2 is a two pole, three

position switch, spring loaded to the center

(OPERATE) position.

2-5. Single Battery Radiacmeters

(a) When S2 is set to ZERO (during zero

The single battery type radiacmeters use a bat-

adjustment of the meter, (2) above), bias voltage

tery and a dc to dc power supply (converter) to

i s removed and the ionization chamber is

develop its required operating voltages. In the

shorted (through R1) to the control grid of V1

schematic diagram (fig. FO-3) the converter is

through connectors P1/J1 pin F, and contacts 5

shown as a separate block on the right-hand

and 2 of S2A. As a result, no potential difference

side. It inputs and outputs on a row of terminals

exists between the ionization chamber and the

numbered 1 through 10. Voltages on the output

control grid of V1.

of the converter are used to bias the ionization

(b) When S2 is set to CHECK (during the

chamber (pin 5), supply plate voltage for V1 (pin

check of radiacmeter circuits), bias voltage is

removed and the ionization chamber is effec-

4) and for checking operation or zeroing the

meter M1.

tively shorted (through R1) to the control grid of

a. Ionization Chamber Bias. Bias for the ioni-

V1. At the same time, the control grid of V1 is

zation chamber is connected through switch S2,

c o n n e c t e d to +1.4 volts from the converter

pins 5 and 3 and 11 and 9. Pin 3 of S2 is connected

through contacts 11 and 10 of S2B. As a result of

to converter pin 5 which supplies positive 2.8

this increase in grid biases of V1, V1 conducts

volts. Pin 5 of S2 is connected to the walls of the

more and the potential at the junction V1, R2

2-4