MIL-PRF-24021K
potential of 26 "4 volts between pins 4 and 5 of the monitor receptacle. The internal circuit
connected to pin 5 shall have a current capacity not less than 1.5 amperes continuously and
15 amperes for 200 milliseconds (msec) at 115 volts AC input. The output shall energize the
aircraft AC external power contactor, thus connecting the AC external power to the aircraft load.
The cyclic peak-to-mean of ripple voltage to the mean level of the monitor DC output voltage shall
be less than 1.5 volts under all input and output conditions.
3.4.3.2 AC monitors excluding power supply. When the external power applied to the
M24021-5 monitor meets the reset conditions specified in 3.4.4.1, the monitor shall, upon
momentary closing of the reset switch, activate a switching circuit or relay which will connect
together pins F and H of the monitor receptacle. The switching circuit between these pins shall
have a DC or AC capacity of at least 5 amperes continuously and 15 amperes for 200 msec. The
switching circuit shall control the application of 26 "4 volts DC or 112.8 to 118.2 volts AC
(externally applied to pin H) to the external power contactor, which will connect external AC power
to the aircraft load. The voltage drop across pins F and H at the monitor receptacle shall be not
greater than 0.25 volt under all input and output conditions.
3.4.3.3 DC monitors. When the external power applied between pins B and A of the
M24021-6 monitor meets the reset conditions specified in 3.4.4.2, the monitor shall, upon
momentary closing of the reset switch, activate a switching circuit between pins G and A which
will apply external power to the aircraft power contactor coil. The switching circuit between pins G
and A shall have a current capacity not less than 2.5 amperes at 28 volts DC and a current capacity
of 15 amperes for 200 msec, which includes the current for the indicator lamp between pin D and
ground. When the switching circuit is closed (power connected to the external power contactor
coil) the voltage drop between pins G and A shall be not greater than 2.5 volts and the indicator
light shall be on under all input and output conditions.
3.4.4 Operating values. Each monitor shall operate as specified in 3.4.4.1 or 3.4.4.2. The
response time specified in 3.4.4.1.1, 3.4.4.2.1, or 3.4.4.2.2, applies to the monitor alone and does
not include the response time of the contactor.
3.4.4.1 Operation of AC monitors. Each AC monitor shall connect the source of AC external
power to the aircraft load via operation of the external power contactor (reset) only when all of the
reset conditions specified in 3.4.4.1.1 and 3.4.4.1.2 are met for all three phase voltages and the reset
switch is momentarily closed. The monitor shall not require the release of the reset switch to
activate its switching circuit. Each AC monitor upon reset shall not connect the load or if in
operation shall disconnect the load (trip) when any one or more of the trip conditions specified in
3.4.4.1.1 and 3.4.4.1.2 are met for any one or more of the three phase voltages. The reset and trip
response times are specified in 3.4.4.1.3 and 3.4.4.1.4.
3.4.4.1.1 Frequency and voltage. Each AC monitor shall have reset and trip response times
for voltage and frequency as specified in table II and on figures 10 and 11.
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