(3)
Input/Output (I/O) PCB
The I/O PCB contains all ECB I/O circuits.
(4)
Connect Module PCB The connect module PCB interconnects all external I/O signals to the related PCB(s). It contains the ARINC 600 connector and the cold junction sensor circuitry (for EGT evaluation).
R **ON A/C 001-003, 051-099, 401-499,
7. Operation/Control and Indication:
_________________________________
A. APU Operation The ECB supplies full authority digital control for all modes of APU operation. The ECB monitors all APU critical parameters, like
-
APU speed,
-
APU temperatures,
-Ambient temperatures,
-Load compressor bleed flow.
This information is used to calculate and continuously control the APU
operation within its different modes.
The control system also includes logics which automatically adjust the
APU operation to reflect variable ambient conditions (e.g. temperature
and altitude (ambient pressure)).
B. APU Control Several major software logics are installed into the ECB to operate and control the APU under various conditions. These major software logics are as follows:
-Fuel Control logic,
-
. Starting logic,
-
. On-speed governor loop,
-IGV control logic,
-SCV control logic,
-Normal shutdown logic
-Protective shutdown logic,
-BITE.
(1)
Fuel Control Logic
The Fuel Control Logic is divided into two sub-logics:
-Starting logic
and
-On-speed governor loop.
(a)
Starting Logic The starting logic accelerates the APU from zero speed (0% rpm) to governed speed (95% rpm) within controlled EGT limits. The starting logic provides 'required-to-run' fuel to the APU, in relation to a given schedule (ramp), by computing the FCU Torque Motor current.
(b)
On-speed Governor Loop During governed APU speed the on-speed governor loop controls the fuel flow to the APU. This keeps a constant APU speed (99% rpm or 101% rpm). The fuel flow is limited by programmed min. and max. fuel schedules.
(2)
IGV Control Logic The ECB measures the IGV position set-point in relation to the APU operation mode. This set-point is dependent on three factors:
-
APU operating mode (i.e. MES, ECS etc.)
-
APU inlet temperature (T2),
-Inlet pressure (P2) The ECB gets feedback from the IGVs LVDT and computes and corrects the commanded position every 20 mS. When the EGT reaches the OVERTEMP limit the IGV setpoint is reduced in order to decrease the mechanical load on the APU.
(a)
ECS Mode The ECS mode operates when the APU BLEED pushbutton switch is pushed and the air conditioning packs are in operation. Then the Zone Controller 8HK sends the ECS demand through the ARINC 429
bus to the ECB (Ref. 21-63-00). This sets the Inlet Guide Vanes (IGV) position in proportion to the ECS demand signal. The ECS min position corresponding to zero % demand depends on T1 and T2.
(b)
MES Mode The MES mode operates when the APU BLEED pushbutton switch is pushed and a main engine start is initiated (Ref. 73-25-00). Then the FADEC sends a signal to the ECB. This sets the IGV position in a fixed position in proportion to the inlet temperature and the T5 trim schedule. When the engine starter valve closes, the FADEC removes the MES signal to the ECB and the ECB switches back to the normal operation mode.
(3)
SCV Control Logic The SCV control logics prevents load compressor surge for all modes of APU operation, ambient conditions (T2/P2) and A/C airflow requirements. The ECB gets feedback from the SCV LVDT, computes the commanded position and corrects the current position in a certain time frame.
**ON A/C 001-003, 051-062,
(4) Performance Adjustments The performance adjustments are used in the IGV control logic, except the adjustment of the cool-down timer. These adustments are electronic switches within the ECB and can be change only by use of a remote terminal through the RS232 interface of the ECB.
(a) Table 2 Performance Adjustments
----------------------------------------------------------------------
| | Adjustment | IGV Position |
| Adjustment | Setting | (volts) |
|-----------------------|----------------------|-----------------------|
| MES adjust | (1) | 9.57 |
| | (2) | 9.57 |
| | (3) | 9.57 |
| | (4) | 9.57 |
| | (5)* | 9.57 |
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