1 0 - 1. PURPOSE   AND   FUNCTION   OF    ENGINE AND   GENERATOR   CONTROLS   AND   INSTRU- MENTS.  (cont) b. Functional Theory of Operation. (cont) microprocessor. Drive is converted into an analog signal that controls a pulse  width  modulator. If the speed value is too high, the drive signal is decreased and the pulse width modu- lation  output  duty  cycle  decreases. (4) Contactor enabling Con- tactor enabling is the process by which generated power is supplied to the load. As  the  engine  continues  to accelerate, its speed is monitored by the EECM microprocessor until 100 percent  speed  is  reached. The  fact that 100 percent speed has been reached is determined by the microprocessor which compares a stored value for 100 percent speed with the actual value on the speed signal line. When that point is reached, the engine is turning the generator at a rate where the generator power output is sufficient to supply the load (start the aircraft). At 100 percent power, the microprocessor outputs a level on one of the four status/control lines  to  the  switch card. After buffering, this becomes the generator enable signal which actuates  a lamp driver circuit. Generator enable is also sent off the card through connector P4 to the GECM to enable the GECM to control the generator. The  lamp  driver  generates the ready to load signal that is routed from the EECN to the control panel causing the READY TO LOAD lamp to come on. When the operator sees the READY TO LOAD  lamp  come  on,  he  places  the CONTACTOR switch momentarily in the CLOSED position, then releases it back to the normal center position. This places +24 Vdc on the (Contactor On) line to the switch card where it is ARMY TM     5-6115-612-34 MARINE   CORPS   TM   6115-34/8 AIR FORCE TO    35C2-3-471-2 NAVY AG-320B0-MME-000 shaped, then used to set a latch on the switch  circuit  card. The set output of the latch is applied to a contactor gate and buffer where it is gated with a contactor enable output that the microprocessor generates at this time. The resulting gate output drives a contactor relay driver which in turn outputs  an  enabling  contactor  enable level. After routing this signal through and out of the control panel unaltered, it  becomes  the  contactor enable level to the output contactor. This level energizes the  contactor relay, allowing power to flow from the generator through the closed contactor relay contacts to the aircraft being started. To show the operator that the relay is closed, closure of another set of relay contacts applies +24 Vdc through  control  panel  terminal  board TB1 to the CONTACTOR CLOSED lamp. The lamp comes  on to verify that the contactor  relay  is  energized. (5)  Output power control. The operator can monitor the voltage and current being supplied to the air- craft. He is also able to regulate the voltage output  of the generator. Voltage is displayed on the control panel VOLTAGE meter, while current is shown on the OUTPUT CURRENT meter. Output voltage is controlled by turning the control panel VOLTAGE ADJUST knob. The changing resistance caused by turning the knob is routed to the GECM to regulate the generator voltage adjust  level. The operator adjusts the knob while watching the VOLTAGE meter until the meter reading is correct. Additionally, the HOURMETER is con- nected across the VOLTAGE meter so that it accumulates the number of hours that voltage  has  been  generated  by  the generator set. 10-5