Section Il. EQUIPMENT DESCRIPTION AND DATA

TM 3-4240-284-30&P

Section Il. EQUIPMENT DESCRIPTION AND DATA

1-6. DESCRIPTION AND TABULATED DATA. Refer

to TM 3-4240-284-20&P.

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

illustrated in appendix B of this manual.

Section IV. PRINCIPLES OF OPERATION

1-10. PRESSURE CONTROL SYSTEM.

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

operational amplifier (op amp) on the switching card

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