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DEFINITIONS
This is the safety alert symbol. It is used to alert you to potential personal
injury hazards. Obey all safety messages that follow this symbol to avoid
possible injury or death.
DANGER—Indicates a hazardous situation which, if not avoided, will result in death
or serious injury.
WARNING—Indicates a hazardous situation which, if not avoided, could result in
death or serious injury.
CAUTION—Indicates a hazardous situation which, if not avoided, could result in
minor or moderate injury.
NOTICE—Indicates a hazard that could result in property damage only (including
damage to the control).
IMPORTANT—Designates an operating tip or maintenance suggestion.
The engine, turbine, or other type of prime mover should be equipped with an
overspeed shutdown device to protect against runaway or damage to the prime
mover with possible personal injury, loss of life, or property damage.
The overspeed shutdown device must be totally independent of the prime mover
control system. An overtemperature or overpressure shutdown device may also
be needed for safety, as appropriate.
Read this entire manual and all other publications pertaining to the work to be performed before
installing, operating, or servicing this equipment. Practice all plant and safety instructions and
precautions. Failure to follow instructions can cause personal injury and/or property damage.
This publication may have been revised or updated since this copy was produced. To verify that
you have the latest revision, be sure to check the Woodward website:
www.woodward.com/pubs/current.pdf
The revision level is shown at the bottom of the front cover after the publication number. The latest
version of most publications is available at:
www.woodward.com/publications
If your publication is not there, please contact your customer service representative to get the
latest copy.
Any unauthorized modifications to or use of this equipment outside its specified mechanical,
electrical, or other operating limits may cause personal injury and/or property damage, including
damage to the equipment. Any such unauthorized modifications: (i) constitute "misuse" and/or
"negligence" within the meaning of the product warranty thereby excluding warranty coverage
for any resulting damage, and (ii) invalidate product certifications or listings.
To prevent damage to a control system that uses an alternator or batter
y
-charging
device, make sure the charging device is turned off before disconnecting the battery
from the system.
To prevent damage to electronic components caused by improper handling, read
and observe the precautions in Woodward manual 82715, Guide for Handling and
Protection of Electronic Controls, Printed Circuit Boards, and Modules.
Revisions—Text changes are indicated by a black line alongside the text.
Woodward Governor Company reserves the right to update any portion of this publication at any time. Information
provided by Woodward Governor Company is believed to be correct and reliable. However, no responsibility is assumed
by Woodward Governor Company unless otherwise expressly undertaken.
© Woodward 1997
All Rights Reserved

Manual 85017V1 505 Digital Governor
Woodward i
Contents
ELECTROSTATIC DISCHARGE AWARENESS ..................................................V
CHAPTER 1. GENERAL INFORMATION...........................................................1
Introduction.............................................................................................................1
General Description................................................................................................3
505 Inputs and Outputs ..........................................................................................5
Control Overview ....................................................................................................6
Speed Control.........................................................................................................9
Auxiliary Control .....................................................................................................9
Load Sharing Input ...............................................................................................10
Cascade Control...................................................................................................10
Valve Limiter.........................................................................................................10
Starting Features ..................................................................................................11
Critical Speed Avoidance .....................................................................................11
Block Diagrams ....................................................................................................12
Keypad and Display..............................................................................................14
Watchdog Timer/CPU Fault Control.....................................................................16
CHAPTER 2. INSTALLATION PROCEDURES..................................................17
Introduction...........................................................................................................17
Mechanical Data and Hardware Installation.........................................................17
Communications Grounding and Shielding..........................................................33
CHAPTER 3. 505 CONTROL DESCRIPTION..................................................35
Introduction...........................................................................................................35
Turbine Start.........................................................................................................35
Turbine Start Modes .............................................................................................37
Critical Speed Avoidance .....................................................................................40
Idle/Rated .............................................................................................................41
Automatic Start Sequence....................................................................................42
No Idle Programmed ............................................................................................45
Speed Control Overview.......................................................................................45
Speed PID Operational Modes.............................................................................46
Cascade Control...................................................................................................58
Auxiliary Control ...................................................................................................64
Remote Auxiliary Setpoint ....................................................................................68
Valve Limiter.........................................................................................................70
Emergency Shutdown ..........................................................................................70
Controlled Shutdown ............................................................................................71
Overspeed Test Function .....................................................................................72
Local/Remote Function.........................................................................................73
Function Keys.......................................................................................................74
Relays...................................................................................................................74
CHAPTER 4. CONFIGURATION PROCEDURES..............................................77
Program Architecture............................................................................................77
Programming the 505 ...........................................................................................78
Exiting the Program Mode..................................................................................101
Valve/Actuator Calibration & Test ......................................................................105
Calibration/Stroking Procedure ..........................................................................106
Calibration/Stroking Procedure ..........................................................................108

505 Digital Governor Manual 85017V1
ii Woodward
Contents
CHAPTER 5. 505 OPERATION...................................................................112
Run Mode Architecture.......................................................................................112
Keypad and Display............................................................................................116
Run Mode Front Panel Keys ..............................................................................116
Starting Procedures............................................................................................117
Speed Key Screens............................................................................................118
Overspeed Test Function ...................................................................................122
F3 and F4 Keys ..................................................................................................123
Limiter (LMTR) Key Screens ..............................................................................123
Actuator (ACTR) Key Screens............................................................................124
Control (CONT) Key Screens .............................................................................125
Dynamics (DYN) Key Screens ...........................................................................127
Stop Key Screens...............................................................................................128
Auxiliary (Aux) Key Screens ...............................................................................128
Remote/Speed Bias (RMT) Key Screens ...........................................................131
Unit Load (KW) Key Screens..............................................................................134
Cascade (CAS) Key Screens .............................................................................135
Alarms.................................................................................................................137
Trips....................................................................................................................138
Speed, Cascade, and Auxiliary Dynamics Adjustments.....................................139
CHAPTER 6. COMMUNICATIONS................................................................143
Modbus Communications ...................................................................................143
Port Adjustments ................................................................................................146
505 Control Modbus Addresses .........................................................................146
Specific Address Information..............................................................................157
CHAPTER 7. SERVICE OPTIONS................................................................159
Product Service Options.....................................................................................159
Woodward Factory Servicing Options ................................................................160
Returning Equipment for Repair .........................................................................161
Replacement Parts .............................................................................................161
Engineering Services..........................................................................................162
How to Contact Woodward.................................................................................162
Technical Assistance..........................................................................................163
APPENDIX.505 PROGRAM MODE WORKSHEETS ......................................164
DECLARATIONS .......................................................................................167

Manual 85017V1 505 Digital Governor
Woodward iii
Illustrations and Tables
Figure 1-1. Typical Single or Dual Inlet Steam Turbine .........................................4
Figure 1-2. Split Range or Admission Type of Turbine Configuration....................4
Figure 1-3a. Overview of 505 Functionality............................................................7
Figure 1-3b. Overview of 505 Functionality............................................................8
Figure 1-4. Overview of 505 Functionality Notes .................................................12
Figure 1-5. Single or Split-Range Turbine Configurations ...................................13
Figure 1-6. Single or Split-Range Turbine Configurations ...................................13
Figure 1-7. Single or Split-Range Turbine Configurations ...................................14
Figure 1-8. 505 Key Pad and Display...................................................................14
Figure 2-1. 505 Control Layout (Standard Enclosure) .........................................19
Figure 2-2. 505 Bulkhead-Mounted Enclosure.....................................................20
Figure 2-3. Jumper Options..................................................................................21
Figure 2-4. Jumper Locations...............................................................................21
Figure 2-5. CageClamp Terminal Blocks .............................................................23
Figure 2-6. Control Wiring Diagram......................................................................24
Figure 2-7. Representative 505 I/O Schematic ....................................................25
Figure 2-8. Fuse location......................................................................................26
Figure 2-9. Shielded Wire Connections................................................................27
Figure 2-10. Typical RS-232 Communications.....................................................32
Figure 2-11. Typical RS-422 Communications.....................................................32
Figure 2-12. Typical RS-485 Communications.....................................................33
Figure 2-13. Preferred Multipoint Wiring with a Separate Signal Ground Wire....33
Figure 2-14. Alternate Multipoint Wiring without a Separate Signal Ground
Wire .................................................................................................34
Figure 3-1. Basic Control Overview......................................................................35
Figure 3-2. Manual Start Mode Example..............................................................38
Figure 3-3. Semiautomatic Start mode Example..................................................39
Figure 3-4. Automatic Start Mode Example .........................................................40
Figure 3-5. Idle/Rated Start ..................................................................................42
Figure 3-6. Automatic Start Sequence .................................................................43
Figure 3-7. Speed Control Functional Diagram....................................................46
Figure 3-8. Speed PID Control Modes .................................................................47
Figure 3-9. Frequency and Unit Load Relationship..............................................49
Figure 3-10. Speed Relationships ........................................................................51
Figure 3-11. Loadsharing Logic............................................................................57
Figure 3-12. Cascade Functional Diagram...........................................................59
Figure 3-13. Aux Control Overview ......................................................................64
Figure 4-1. Basic Program Architecture ...............................................................77
Figure 4-2. Initial 505 Program Mode Entry .........................................................78
Figure 4-3a. Program Mode Blocks......................................................................81
Figure 4-3b. Program Mode Blocks......................................................................82
Figure 4-3c. Program Mode Blocks......................................................................83
Figure 4-3d. Program Mode Blocks......................................................................84
Figure 4-4. Exiting the Program Mode ...............................................................101
Figure 4-5. Stroke Actuator ................................................................................110
Figure 4-6. Stroking Dual Actuators ...................................................................111
Figure 5-1. Basic Program Architecture .............................................................112
Figure 5-2a. Overview of Run Mode ..................................................................113
Figure 5-2b. Overview of Run Mode ..................................................................114
Figure 5-3. 505 Keypad and Display ..................................................................116
Figure 5-4. SPEED Key Screens .......................................................................118
Figure 5-5. Direct Setpoint Entry ........................................................................121
Figure 5-6. Overspeed Test Enable Key Screens..............................................122
Figure 5-7. LMTR Key Screens..........................................................................124

505 Digital Governor Manual 85017V1
iv Woodward
Illustrations and Tables
Figure 5-8. ACTR Key Screens ..........................................................................125
Figure 5-9. CONT Key Screens..........................................................................126
Figure 5-10. DYN Key Screens ..........................................................................127
Figure 5-11. STOP Key Screens ........................................................................128
Figure 5-12. AUX Key Screens ..........................................................................129
Figure 5-13. RMT Key Screens ..........................................................................132
Figure 5-14. KW Key Screens ............................................................................134
Figure 5-15. CAS Key Screens ..........................................................................135
Figure 5-16. ALARM Screen ..............................................................................137
Figure 5-17. TRIP Screen...................................................................................138
Figure 5-18. Typical Response to Load Change................................................142
Figure 6-1. ASCII/RTU Representation of 3.......................................................144
Figure 6-2. Modbus Frame Definition.................................................................145
Table 1-1. 505s with Polyacrylate Coated Boards .................................................1
Table 2-1. Jumper Options Chart .........................................................................22
Table 3-1. On-Line/Off-Line Dynamics Selection .................................................53
Table 3-2. Load Sharing Logic .............................................................................58
Table 4-1. Actuator Driver Limits ........................................................................106
Table 5-1. Overview of Run Mode......................................................................115
Table 5-2. Idle/Rated Messages.........................................................................119
Table 5-3. Auto Start Messages .........................................................................120
Table 5-4. Controlling Parameter Messages......................................................126
Table 5-5. Auxiliary Messages (if using Aux enable) .........................................130
Table 5-6. Auxiliary Messages (if using Aux as a limiter)...................................130
Table 5-7. Remote AUX Messages....................................................................131
Table 5-8. Remote Speed Messages.................................................................132
Table 5-9. Control Messages .............................................................................133
Table 5-10. Cascade Control Messages ............................................................136
Table 5-11. Remote Cascade Messages ...........................................................137
Table 5-12. Alarm Messages..............................................................................138
Table 5-13. Trip Messages.................................................................................139
Table 6-1. ASCII vs RTU Modbus ......................................................................144
Table 6-2. Modbus Function Codes ...................................................................145
Table 6-3. Modbus Error Codes .........................................................................146
Table 6-4. Maximum Modbus Discrete and Analog Values ...............................147
Table 6-5. Boolean Write Addresses..................................................................148
Table 6-6. Boolean Read Addresses .................................................................150
Table 6-7. Analog Read Addresses ...................................................................152
Table 7-8. Analog Write Addresses....................................................................152
Table 6-9. Last Turbine Trip Cause....................................................................153
Table 6-10. Control Status..................................................................................153
Table 6-11. Analog Input Configuration..............................................................154
Table 6-12. Analog Output Configuration...........................................................154
Table 6-13. Relay Configuration.........................................................................155
Table 6-14. Contact Input Configurations...........................................................156
Table 6-15. Units Configuration..........................................................................156

Manual 85017V1 505 Digital Governor
Woodward v
Electrostatic Discharge Awareness
All electronic equipment is static-sensitive, some components more than others.
To protect these components from static damage, you must take special
precautions to minimize or eliminate electrostatic discharges.
Follow these precautions when working with or near the control.
1. Before doing maintenance on the electronic control, discharge the static
electricity on your body to ground by touching and holding a grounded metal
object (pipes, cabinets, equipment, etc.).
2. Avoid the build-up of static electricity on your body by not wearing clothing
made of synthetic materials. Wear cotton or cotton-blend materials as much
as possible because these do not store static electric charges as much as
synthetics.
3. Keep plastic, vinyl, and Styrofoam materials (such as plastic or Styrofoam
cups, cup holders, cigarette packages, cellophane wrappers, vinyl books or
folders, plastic bottles, and plastic ash trays) away from the control, the
modules, and the work area as much as possible.
4. Do not remove the printed circuit board (PCB) from the control cabinet
unless absolutely necessary. If you must remove the PCB from the control
cabinet, follow these precautions:
Do not touch any part of the PCB except the edges.
Do not touch the electrical conductors, the connectors, or the
components with conductive devices or with your hands.
When replacing a PCB, keep the new PCB in the plastic antistatic
protective bag it comes in until you are ready to install it. Immediately
after removing the old PCB from the control cabinet, place it in the
antistatic protective bag.
To prevent damage to electronic components caused by improper
handling, read and observe the precautions in Woodward manual
82715, Guide for Handling and Protection of Electronic Controls,
Printed Circuit Boards, and Modules.

505 Digital Governor Manual 85017V1
vi Woodward

Manual 85017V1 505 Digital Governor
Woodward 1
Chapter 1.
General Information
Introduction
This manual describes the Woodward 505 Digital Governor for steam turbines.
English versions are 9907-162, 9907-163, and 9907-164. The option charts
below show the differences between the part numbers. Volume 1 of this manual
provides installation instructions, describes the control, and explains the
configuration (programming) and operating procedures. Volume 2 includes notes
on applying the control to specific applications, Service mode information, and
505 hardware specifications. This manual does not contain instructions for the
operation of the complete turbine system. For turbine or plant operating
instructions, contact the plant-equipment manufacturer.
Manual 85018 describes the 505E Digital Governor for extraction steam turbines.
Part Number Options
Part Number Power
9907-162 HVAC (180–264 Vac)
9907-163 AC/DC (88–132 Vac or 90–150 Vdc)
9907-164 LVDC (18–32 Vdc)
Optional Bulkhead Mounting Box (NEMA 4X) P/N 8923-439
505 controllers now utilize a special polyacrylate conformal coating material to
coat and protect their internal circuit boards from corrosive environments. This
new polyacrylate material replaces the previous silicon conformal coating and
provides an improved barrier between board components and sulfur-based
gases. 505 controls that have this coating will have a label on the side stating
“SULFUR RESISTANT CONFORMAL COATED”. All 505 controllers shipped
from Woodward with the revision letters listed below, or subsequent letters, were
shipped with the new polyacrylate conformal coating material:
Table 1-1. 505s with Polyacrylate Coated Boards
Part Number Revision Label on 505
9907-162 U 9907-162U
9907-163 U 9907-163U
9907-164 R 9907-164R
9907-805 K 9907-805K
9907-806 K 9907-806K
9907-807 K 9907-807K
9907-813 D 9907-813D
9907-814 D 9907-814D
9907-815 D 9907-815D

505 Digital Governor Manual 85017V1
2 Woodward
General Installation and Operating Notes and Warnings
This equipment is suitable for use in Class I, Division 2 , Groups A, B, C, and D
(Class I, Zone 2, Group IIC) or non-hazardous locations.
The 505s are suitable for use in European Zone 2, Group II environments per
compliance with EN60079-15, Electrical apparatus for explosive atmospheres –
Type of protection ‘n’
These listings are limited only to those units bearing the certification
identification.
Field wiring must be rated at least 75 °C for operating ambient temperatures
expected to exceed 50 °C.
Peripheral equipment must be suitable for the location in which it is used.
Wiring must be in accordance with North American Class I, Division 2 or
European Zone 2 wiring methods as applicable, and in accordance with the
authority having jurisdiction.
EXPLOSION HAZARD—Do not connect or disconnect while circuit is
live unless area is known to be non-hazardous.
Substitution of components may impair suitability for Class I,
Division 2.
Do not use any test points on the power supply or control boards
unless the area is known to be non-hazardous.
RISQUE D’EXPLOSION—Ne pas raccorder ni débrancher
tant que l’installation est sous tension, sauf en cas
l’ambiance est décidément non dangereuse.
La substitution de composants peut rendre ce matériel
inacceptable pour les emplacements de Classe I, Division 2.
Ne pas utiliser les bornes d’essai du block d’alimentation
ou des cartes de commande à moins de se trouver dans un
emplacement non dangereux.

Manual 85017V1 505 Digital Governor
Woodward 3
505 Software Changes Covered in This Manual Revision
1. PROGRAM MODE: Added an error check to ensure Rated Speed (when
programmed as a gen set) was less than max gov.
2. SERVICE MODE: Changed the hold changes for Min Load to come from the
Breaker Logic header's Hold Changes input. Previously the hold changes
command was selected under the Speed Control Settings header.
3. SPEED SETPOINT RATES: Changed the minimum adjustment range for all
speed setpoint rates to 0.01 (was 0.1).
4. AUX LIMITER or CONTROLLER: Added logic to ensure the inhibited status
of Aux control when the input is failed. In addition, changed Aux re- enable
logic such that when a failed aux input is restored there is no glitch to the
speed LSS. Also changed breaker open logic to correct a Gen Opening Aux
actuator output glitch.
5. AUX CONTROLLER: Changed the speed setpoint aux biasing logic to only
allow the speed control limiting action (while in aux control) to be active when
the speed setpoint reaches max gov. Prior to this fix the speed limiter could
come into control during an extreme transient.
6. AUX DIRECT ENTERED SETPT: Changed Aux Entered setpoint to be
reset/stopped on a shutdown pulse rather than held disabled on a shutdown
condition. This change allows the Aux Limiter function direct setpoint entry
even when the unit is tripped.
7. AUX and CASC DROOP: Changed the droop feedback lag-tau tunable range
from a max of 10 to a max of 1000.
8. MODBUS: Changed the Gen and Tie Open alarms for Aux, Casc, and
Remote to match the Modbus listing—the software eventlatch inputs were
reversed/backwards with the Modbus listing.
9. CONTROLLED STOP: Made the Controlled Stop abort if speed raise/lower is
selected or another control mode is selected. This can be tuned-out by
setting CNTRL_STOP.RL_STOP.IN_2=*false in the debug mode.
10. ANALOG INPUTS: Changed max setting on the delay time’s tunable range
from 3 ms to 3000 ms. The analog input failure delay setting is defaulted to
zero but can be adjusted up to 3000 ms using the debug mode
MAIN.AIx.LATCH_DLY where x is the analog input number. Added a tunable
single pole filter (LAG) to each analog input. Output/input = 1/(1+st) where t =
1/(2(pi)f) = LAG_TAU. The Lag-tau is defaulted to zero but can be adjusted
in the debug mode using MAIN.AIx_LAG.LAG_TAU where x is the analog
input number (1-6).
General Description
General
The 505 microprocessor-based control is designed to control single or dual (split
range) actuator steam turbines (extraction steam turbines require the 505E
version). The 505 is field programmable which allows a single design to be used
in many different control applications and reduces both cost and delivery time. It
uses menu driven software to instruct site engineers on programming the control
to a specific generator or mechanical drive application. The 505 can be
configured to operate as a stand-alone unit or in conjunction with a plant’s
Distributed Control System.

505 Digital Governor Manual 85017V1
4 Woodward
INLET
STEAM
T&T
VALVE
EXHAUST
855−664
VALVE
T&T
GOVERNOR VALVE
STEAM
INLET
98−03−12 JMM
GOVERNOR VALVE
STEAM
Figure 1-1. Typical Single or Dual Inlet Steam Turbine
GOVERNOR VALVE
INLET
STEAM
T&T
VALVE
EXHAUST
STEAM
855−665
VALVE
T&T
GOVERNOR VALVE
STEAM
INLET
HP/ACT1
LP/ACT2 98−03−12 JMM
Figure 1-2. Split Range or Admission Type of Turbine Configuration
Operator Control Panel
The 505 is a field configurable steam turbine control and operator control panel
(OCP) integrated into one package. A comprehensive operator control panel,
including a two-line (24 characters each) display, and a set of 30 keys is located
on the 505’s front panel. This OCP is used to configure the 505, make On-Line
program adjustments, and operate the turbine/system. Easy to follow instructions
are presented in English through the OCP’s two-line display and operators can
view actual and setpoint values from the same screen.

Manual 85017V1 505 Digital Governor
Woodward 5
Turbine Control Parameters
The 505 interfaces with one or two control valves to control one parameter at a
time and limit an additional parameter, if desired. The one controlled parameter is
typically speed (or load), however, the 505 could be utilized to control or limit:
turbine inlet pressure or flow, exhaust (back) pressure or flow, first stage
pressure, generator power output, plant import and/or export levels, compressor
inlet or discharge pressure or flow, unit/plant frequency, process temperature, or
any other turbine related process parameter. Refer to Volume 2 of this manual
for details on applications.
Communications
The 505 can communicate directly with plant Distributed Control Systems and/or
CRT based operator control panels, through two Modbus®* communication
ports. These ports support RS-232, RS-422, or RS-485 communications using
ASCII or RTU MODBUS transmission protocols. Communications between the
505 and a plant DCS can also be performed through hardwired connections.
Since all 505 PID setpoints can be controlled through analog input signals,
interface resolution and control is not sacrificed.
*—Modbus is a trademark of Schneider Automation Inc.
Additional Features
The 505 also provides the following features: First-Out Trip Indication (5 total trip
inputs), Critical Speed Avoidance (2 speed bands), Auto Start Sequence (hot &
cold starts), Dual Speed/Load Dynamics, Zero Speed Detection, Peak Speed
Indication for Overspeed trip, and Isochronous Loadsharing between units (with a
DSLC™ control).
Using the 505
The 505 control has two normal operating modes, the Program Mode and the
Run Mode. The Program Mode is used to select the options needed to configure
the control to your specific turbine application. Once the control has been
configured, the Program Mode is typically never again used, unless turbine
options or operation changes. Once configured, the Run Mode is used to operate
the turbine from start-up through shutdown. In addition, on-line adjustments can
be made using the Service Mode (see Volume 2).
505 Inputs and Outputs
Control Inputs
Two speed inputs that are jumper configurable for MPU (magnetic pickup units)
inputs or proximity probes.
Six programmable analog inputs can be used as one of the following options:
auxiliary input, remote auxiliary setpoint, cascade input, remote cascade setpoint,
kW (load) input, remote speed setpoint, synchronizing, load sharing, both
synchronizing and load sharing, and first stage pressure. The sixth analog input
has isolation circuitry and should be used for a self-powered signal that is not
isolated.

505 Digital Governor Manual 85017V1
6 Woodward
Sixteen contact inputs are available. Four are dedicated for shutdown, reset,
raise speed setpoint, and lower speed setpoint. Another two contact inputs must
be dedicated for generator breaker and utility tie breaker if the control is used in a
generator application. Ten additional contact inputs can be configured. If the unit
is not used in a generator application, then twelve additional contact inputs can
be configured.
Four function keys on the front panel of the control. F1 and F2 are dedicated to
alarm and overspeed, respectively. F3 and F4 can be used to enable or disable
various functions of the control.
Control Outputs
Two actuator outputs with linearization curves; the second actuator output can be
used as an extra readout if not used as an actuator output. Six 4–20 mA outputs,
for meters or other readouts.
Eight Form-C relay contact outputs, six that are configurable. The two dedicated
relay outputs are for shutdown and alarm indication.
Control Interfaces
Two Modbus ports, to be used as control interfaces. The protocol can be either
ASCII or RTU and the communications can be RS-232, RS-422, or RS-485.
One computer (PC) port to be used for program configuration storage.
An overview of the 505 functions is shown in Figure 1-3. Use this block diagram
to match the control features to the site-specific application required.
Control Overview
The 505 has two independent control channels, the speed/load and auxiliary
controllers. The outputs of these two controllers are low-signal-selected (LSS)
with another channel, the valve limiter. The output of the LSS directly sets the
position of the actuator driver’s output. In addition to these channels, the
speed/load controller can be manipulated by another controller, the cascade
controller. The cascade controller is ‘cascaded’ into the speed controller,
whereby the speed controller setpoint is changed directly by the cascade
controller output. The auxiliary controller can act as either a control channel or as
a limiting channel. All three of these PID controllers have the option of utilizing an
analog input signal to remotely position their setpoints. Additional features of the
505 include frequency control, isochronous loadsharing (with a DSLC), critical
speed avoidance, idle/rated control and an automatic start sequence. There are
two serial communications ports which can be used to monitor and control the
turbine using Modbus protocol.

Manual 85017V1 505 Digital Governor
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Figure 1-3a. Overview of 505 Functionality

505 Digital Governor Manual 85017V1
8 Woodward
Figure 1-3b. Overview of 505 Functionality

Manual 85017V1 505 Digital Governor
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Speed Control
The speed control receives a turbine speed signal from one or two magnetic
pickups or proximity probes. The speed PID (proportional, integral, derivative)
control amplifier then compares this signal to the speed setpoint to generate an
output signal to the actuator (through a low signal select bus).
The speed control’s setpoint is adjustable with raise or lower commands through
the keypad on the front of the control, remote contact inputs or the
communication line. The setpoint can also be directly set by entering the new
setpoint from the keypad or through either Modbus communications. In addition,
an analog input can be programmed to remotely position the speed setpoint.
Remote Speed Setpoint
One of the 4–20 mA inputs can be configured to control the speed setpoint.
Typically, a process control external to the 505 interfaces with this input to
regulate the turbine’s speed or load to control a related process.
The remote speed setpoint input directly affects the 505’s speed setpoint. The
maximum rate at which the remote input signal can change the speed setpoint is
programmable. When the remote setpoint is enabled, the speed setpoint will
move at a much slower rate until the two settings are matched at which time the
speed setpoint will be allowed to move at the maximum rate. The remote speed
function can be enabled and disabled as required from the front-panel keypad,
remote contact inputs or the communication line.
Auxiliary Control
The Auxiliary control channel can be used to either control a parameter or limit a
parameter. The Auxiliary PID controller can be used to control or limit unit
load/power, plant import/export levels, inlet pressure, exhaust pressure,
temperature or any other process directly related to turbine load.
The Auxiliary input is a 4–20 mA current signal. The Auxiliary PID control
amplifier compares this input signal with a setpoint to produce a control output to
the digital LSS (low-signal select) bus. The LSS bus sends the lowest signal to
the actuator driver circuitry.
The Auxiliary setpoint is adjustable with raise or lower commands through the
keypad on the front of the control, through remote contact inputs or through the
communication links. Also, the setpoint can be directly set by entering the new
setpoint from the keypad or through either Modbus communications. In addition,
an analog input can be programmed to remotely position the Auxiliary setpoint.
Remote Aux Setpoint
One of the 4–20 mA inputs can be configured to remotely adjust the aux setpoint.
The remote aux setpoint input directly affects the Auxiliary setpoint. The
maximum rate at which the remote input signal can change the auxiliary setpoint
is programmable. When the remote setpoint is enabled, the Auxiliary setpoint will
move at a much slower rate until the two settings are matched at which time the
setpoint will be allowed to move at the maximum rate. The remote aux function
can be enabled and disabled as required from the front panel keypad, the remote
contact inputs, or the communication links.

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Load Sharing Input
The 505 is capable of using an analog input to accept a load sharing signal from
Woodward’s Digital Synchronizer and Load Control (DSLC). This input in
conjunction with the DSLC allows the control to isochronously loadshare with any
other system using a DSLC. The 505’s internal summing junction adds this signal
with the speed/load PID’s reference. In addition to loadsharing, the DSLC input to
the 505 can be used to synchronize the unit to either the plant bus or to the utility.
Cascade Control
The cascade control can be configured to control any system process, related to
or affected by turbine speed or load. Typically this controller is used as a turbine
inlet or exhaust pressure controller.
The cascade control is a PID controller that compares a 4–20 mA process signal
with the cascade setpoint. The PID controller sets the speed controller setpoint
until the process signal and the setpoint match.
The cascade setpoint is adjustable with raise or lower commands through the
keypad on the front of the control, the remote contact inputs, or the
communication links. Also, the setpoint can be directly set by entering the new
setpoint from the keypad or through Modbus communications. In addition, a
remote cascade setpoint analog input can be programmed to remotely position
the cascade setpoint.
Remote Cascade Setpoint
One of the 4–20 mA inputs can be configured to remotely adjust the cascade
setpoint. The remote cascade setpoint input directly affects the 505’s cascade
setpoint. The maximum rate at which the remote input signal can change the
cascade setpoint is programmable and can be changed in the Run mode. When
the remote setpoint is enabled, the cascade setpoint will move at a much slower
rate until the two settings are matched at which the setpoint will be allowed to
move at the maximum rate. The remote cascade function can be enabled and
disabled as required from the front-panel keypad, the remote contact inputs or
the communication links.
Valve Limiter
The valve limiter limits the actuator output signal or valve position to aid in
starting up and shutting down a turbine. The output of the valve limiter is low-
signal-selected with the output of the speed/load and auxiliary control channels.
The control or limiter channel asking for the lowest valve position will control
valve position. Thus, the valve limiter limits the maximum valve position. The
valve limiter can be adjusted through the keypad, external contact closures, or
Modbus commands.
The valve limiter can also be used to troubleshoot system dynamics problems. If
it is believed that the 505 is the source of system instability, the valve limiter can
be positioned to manually take control of the valve position. Care should be taken
when using the valve limiter in this fashion, so as to not allow the system to reach
a dangerous operating point.

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Starting Features
The 505 provides options for three different starting modes: automatic, semi-
automatic, and manual. One of these modes must be programmed to get the
turbine from a shutdown state to speed control at minimum speed. The start
mode configured and minimum governor controlling speed will depend on normal
plant starting procedures and turbine manufacturer’s recommendations.
If an idle speed is programmed (either idle/rated or auto start sequence modes),
the 505 can provide automatic speed control and critical speed avoidance. A
‘Run’ command can be given through the 505 keypad, a remote contact input, or
Modbus communications. In addition, an optional ‘Start Permissive’ contact input
can be programmed to prevent a start if, for example, the trip-throttle or stop
valve is not closed.
Idle/Rated
The idle/rated function gives an operator the ability to move between a
programmed idle speed and a programmed rated speed at a configured rate. The
selection of idle or rated speed setpoint positions can be made through the front
panel keypad, through remote contact inputs, or through the Modbus
communications links. The idle/rated function can also be programmed as a
ramp-to-rated function only.
Auto Start Sequence
The auto start sequence function gives the operator the ability to start from a
programmed low idle speed, hold there until the programmed warm-up time has
expired, then go to a programmed high idle speed, hold there until the
programmed high idle warm-up time has expired, and finally move to the
programmed rated speed setpoint. The hold times and the acceleration rates are
dependent on whether the turbine is considered ‘hot’ or ‘cold’ based on the time
the turbine has been shut down. When the turbine is between hot and cold
conditions, the control interpolates between the hot and cold data points to
determine the appropriate startup rates and hold times.
The auto start sequence can be stopped and started, if desired, by programming
and using the auto start sequence halt/continue commands. The selection of halt
or continue can be made through the 505 keypad, remote contact inputs or
Modbus communications. In addition, the auto start sequence can be
programmed to automatically halt at each idle setpoint.
Critical Speed Avoidance
In many turbines, it is desirable to avoid certain speeds or speed ranges (or pass
through them as quickly as possible) due to excessive turbine vibration or other
factors. During programming, two critical speed avoidance bands may be
selected. These bands may be any speed ranges that is less than the minimum
governor speed setting. Either the Idle/Rated or the Auto Start Sequence
functions must be programmed to perform critical speed avoidance. Within a
critical speed range, the 505 moves the speed setpoint at the critical speed rate
programmed and does not allow the speed setpoint to stop within the critical
speed avoidance band. If the turbine is accelerating through a critical avoidance
band and excessively high vibrations are experienced, selecting the speed
setpoint lower command will bring the unit back to the lower limit of the band.

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Block Diagrams
Overviews of possible 505 configurations are shown in Figures 1-5 through 1-7.
Use these block diagrams to match the control features to the site-specific
application requirements. Figure 1-4 lists symbols and their respective
explanations. The Cascade and auxiliary PIDs are optional controllers, and are
shown in the following diagrams for PID relationship purposes only.
Figure 1-4. Overview of 505 Functionality Notes