Woodward GECO, Technical Manual, Page: 34 / 90

GECO

Stoichiometric Manual 03554
26 Woodward
Figure 4-4. Start Sequence Flowchart
In more detail, when the engine is shut down, the speed signal reads 0 speed. At
this time, the fuel valves are closed down to 0%. At cranking, the control looks for
an engine speed of at least 50 rpm before opening the valves to the “Crank
Default” position. The valves remain at this position until the engine accelerates
to approximately 450 rpm. At 450, the valve position control passes to the Valve-
Learn table. The valve position is taken from this table until the Mdot_air
breakpoint is reached. This value will rise as the engine speeds up and load
increases. The “Mdot_air breakpoint” is the value of “Mdot_air” at which the
closed loop control is activated. This value can be set at any level but would
typically be the value that represents approximately 50% load. At this time the
control will move into closed loop operation.
Modbus Communication
The GECO
 Stoichiometric control can serve as a Modbus “slave” unit and will
respond to requests for information from a properly programmed “master.”
The table below gives some examples of the parameters available. A complete
list is available in the Appendix. The register addresses in the proper Modbus
format will provide the numerical or Boolean values. These values must then be
scaled properly for meaningful information.
It is not necessary to read all of the information available. Modbus protocol allows
you to read only the registers of interest.
This function is for information distribution and is not intended or capable of
remote configuration or tuning.
RS-485
Terminals 63 and 64 on the edge of the circuit board are the RS-485 connection.
This is the Modbus communication port.
Valve
Position = 0
Command
Is speed
>
cranking
speed?
BEGIN
NO
NO
Is speed
>
running
speed?
Valve
Position =
Command
YES
YES
Go to Open
Loop
I
s Mdot_air
>
Mdot_air
breakpoint?
NO YES
Go to
Closed
Loop
Crank
Position
Cranking speed is
typically 20 rpm
Running speed is
typically 190 rpm