TM 3-4240-284-30&P
Section Il. EQUIPMENT DESCRIPTION AND DATA
1-6. DESCRIPTION AND TABULATED DATA. Refer
Section Ill. REPAIR PARTS, SPECIAL TOOLS, TMDE, AND SUPPORT EQUIPMENT
1-7. COMMON TOOLS AND EQUIPMENT. For
1-8. SPECIAL TOOLS, TMDE, AND SUPPORT
EQUIPMENT. No special tools, TMDE, or support
authorized common tools and equipment refer to the
Modified Table of Organization and Equipment (MTOE)
equipment are required.
applicable to your unit.
1-9. REPAIR PARTS. Repair parts are listed and
Section IV. PRINCIPLES OF OPERATION
switching card A3, the pressure transducer output vol-
tage drops below the low limit reference voltage. An
a. The basic function of the pressure control system
is to control the air pressure in a protected compartment
compares pressure transducer output voltage to the low
within the prescribed limits by controlling the opening of
limit reference voltage (2.6 volts for the compartment
an airflow valve from the pressurized air supply, the filter
control module low limit side) provided by potentiometer
unit. The prescribed limits are 1.2 to 1.7 inches water
R11, resistor R13 and the voltage reference diode VR1
gage (hereafter referred to as in. wg) for the compart-
and multiplies the voltage difference by 26 times and
ment or compartment control module and 0.4 to 0.8 in.
provides this as the output voltage at TP-D. The op amp
wg for the protective entrance and protective entrance
output voltage is at a low power level of only a few
control module. The control system operates from 28
milliamps (mA). The transistor Q1 amplifies the power
vdc power.
level to about 50 mA while providing no voltage amplifi-
b. The compartment pressure is sensed by the
cation. The power level is further amplified by Q4 of the
pressure transducer which provides an output voltage of
power card Al. This transistor brings the power level up
2 volts/in. wg to pin 1 of the switching card. When the air
to about 500 mA to drive the airflow valve motor.
pressure in the compartment drops below the desired
low limit, 1.2 in. wg for switching card A2 or 0.4 in. wg for
1-2