Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
94
LSS BUS OUTPUT % x ‘EXT/ADM DROOP %’ x ‘MAX SET POINT’ x 0.0001
Example: 25% x 5% x 600 psi x 0.0001 = 7.5 psi
Where the ‘EXT/ADM DROOP %’ is set in Configuration mode, ‘MAX SET POINT’ value is
determined by the upper range limit of the process variable selected and the ‘LSS bus output %’ is
determined by the Ext/Adm demand.
Invert Ext/Adm Input
Depending on the control action required, the Ext/Adm PID’s input signal can be inverted. If a decrease in
control valve position is required to increase the Ext/Adm process signal, program the ‘INVERT EXT/ADM
INPUT’ setting to ‘YES’. In the case of switching to fully decoupled mode, the necessary inversion in
taken care of internally in the control logic, thus in most cases, this parameter should typically not be
adjusted.
Ext/Adm Set Point
The Ext/Adm set point can be adjusted from the keypad, external contacts, Modbus/OPC commands, or
through a 4–20 mA analog input. A specific setting can also be directly entered from the keypad or
through Modbus commands.
The Ext/Adm set point range must be defined in the Configuration mode. Program settings ‘Minimum
Ext/Adm Setpoint’ and ‘Maximum Ext/Adm Setpoint’’ define the range of the Ext/Adm set point and
control.
When a raise or lower Ext/Adm Set Point command is issued, the set point moves at the programmed
‘Ext/Adm Setpoint Rate’ setting. If an Ext/Adm raise or lower command is selected for longer than three
seconds, the Ext/Adm set point will move at three times at the fast rate which is three times the Ext/Adm
set point rate. The Ext/Adm set point rate, fast rate delay, and fast rate can all be adjusted in the Service
mode.
The shortest length of time a set point will move for an accepted raise or lower command is 40
milliseconds (120 milliseconds for a Modbus command
A specific set point may also be directly entered from the 505 keypad or through Modbus/OPC
communications. When this is performed, the set point will ramp at the ‘Ext/Adm Setpoint Rate’ (as
defaulted in Service mode).
To “enter” a specific set point from the 505 Display, use the following steps:
1. From the HOME page go to the Ext/Adm Control page
2. Press the Commands button until ‘Entered Setpoint’ appears
3. Select ‘Entered Setpoint’ and a pop-up will appear
4. Press Enter from the Navigation cross and the pop-up value will highlight
5. Adjust the value with the Adjust keys or enter a value from the keypad
6. Press Enter again when desired value has been entered
7. The value in the pop-up will be accepted, if it is invalid a message will appear
8. Select the GO button to ramp the setpoint to this entered value
Refer to Volume 2 of this manual for further information on Service mode and online tunables. All
pertinent Ext/Adm control parameters are available through the Modbus links. See Chapter 6 for a
complete listing of Modbus parameters.
Remote Ext/Adm Set Point
The Ext/Adm set point can be positioned through an analog signal. Optionally, one of the 505’s analog
inputs can be programmed to position the Ext/Adm PID set point. This allows the Ext/Adm set point to be
positioned remotely by a process control or distributed plant control system.