MIL --- PRF --- 51191G(EA)
control knob. When the control knob is turned fully counterclockwise, no heat shall be sup-
plied to the air stream. The controller assembly shall be totally enclosed and watertight with
all electrical control circuitry (relays, switches, solid state electronics, etc.) sealed inside. The
center line of the controller shall be capable of being moved at least 45 degrees in either
direction (clockwise or counter --- clockwise) to the vertical plane which runs through the lon-
gitudinal axis and is perpendicular to the mounting bracket.
3.3 Operating requirements.
3.3.1 Compatibility with vehicle electrical system. The heater shall be capable of with-
standing normal vehicular voltage surges and spikes such as the following. The heater with
controller shall be capable of withstanding a surge voltage of 39 volts for 10 seconds and re-
cover within 0.015 second. The heater with controller shall meet all requirements in 3.3 after
withstanding a spike voltage of 250 volts for 0.015 milliseconds.
3.3.2 Operability during movement. The heater shall meet all operating requirements in
3.3 when the air inlet and outlet ports are rotated 180 degrees to each side of the vertical posi-
tion. The heater shall not malfunction due to opening or shorting of internal wiring.
3.3.3 Heating capability and power consumption. The heater shall be capable of receiving
4.5 cubic feet per minute (cfm) of air, minimum, (when corrected to standard conditions of
70_F and 1 atm) at its inlet at a temperature of 0 ± 4_F and discharging this air at its outlet
at a minimum temperature of 120_F within 15 minutes after starting heater set to its maxi-
mum output level. Heater shall not consume more than 250 watts of power.
3.3.4 Resistance to airflow. With the heater at ambient room temperature, the resistance
to airflow shall not exceed a differential pressure of 0.10 inches of water.
3.3.5 Operability with thermostatic control. The heater shall operate in a room tempera-
ture environment of 70_F and be capable of producing a regulated outlet air temperature of
120±4_F for input voltage of 24 to 30 Volts direct current (Vdc) and 115.5±8.5_F for input
voltage of 18 Vdc within 10 minutes of operation when the inlet air flow rate is 4.5 cfm. The
heater shall maintain those outlet air temperatures for a period of not less than 5 minutes
without adjustment of the controller. During these conditions, the case temperature shall not
exceed 126_F.
3.3.6 Leakage resistance. Air leakage shall be not greater than 1.00 cubic inch (16.4 cubic
centimeters) per minute when the filter is internally pressurized to at least 12 inches (30.5
centimeters) of water. Teflont or polytetrafluoroethylene tape shall be applied to the
threads of the plugs if this prevents sticking or leakage around plugs.
3.3.7 Electromagnetic emissions. The heater shall not produce electromagnetic emissions
of such magnitude that mission essential communications equipment and electronic systems
are adversely effected. Measured electromagnetic emission levels shall be within the limits
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