anti-icing solenoid valve, starting fuel solenoid valve, oil level indicator, and power turbine tachometer
generator. The main disconnect plug mates with an electrical receptacle of the airframe wiring,
establishing electrical continuity to the various airframe components.
b.
Ignition exciter. The high-potential ignition pulse is developed by the ignition exciter;
24 volts dc is applied to the input of the exciter. Current flows through the primary transformer
winding the bias coil and the vibrator points to ground. This generates magnetic lines of force which
permeate the transformer core and the core of the bias coil attracting the vibrator reed upward and
interrupting the circuit. As current flow ceases, the lines of force collapse and the reed falls back,
closing the circuit. This cycle repeats at a rate proportional to the input voltage. The resultant current
flows in pulses, causing magnetic lines of force to build up and collapse with each pulsation. These lines
induce voltage across the secondary coil which is transformed to a higher potential by an increased
number of windings comprising the secondary. The diodes rectify the pulsating current back into direct
current to charge the capacitors. The charge on the capacitors continues to build up at a rate
proportional to input voltage, until a potential of 2,500 volts exists. The calibrated spark gaps ironize at
this voltage, creating an electrical path for the firing pulse. The capacitors discharge through this path
into the lead and coil assembly for distribution to each of the spark igniters.
Radio frequency energy is generated within the exciter during normal operation. An
inductive capacitive filter has been incorporated at the input to prevent this energy from being fed back
into the 24-volt input line. Radio frequency interference on this line could be detrimental to the
operation of other electrical accessories. This filter is tuned to radio frequencies and does not offer any
appreciable opposition to the flow of 24-volt direct current.
c.
Ignition lead and coil assembly. The ignition lead and coil assembly constitutes the
high-potential ignition wiring. This assembly incorporates two coils, fed with high voltage from the two
outputs of the ignition exciter. The coil assemblies function as spark splitters distributing high voltage to
four igniter plugs. Each coil assembly has one input and two outputs with the coil windings forming a
transformer having a 1:1 ratio. Any current flowing through either winding will induce a voltage across
the other so that even a shorted igniter plug will not short out the high-voltage ignition signal. The
entire wiring harness is shielded and grounded at the airframe to suppress radio frequency interference.
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