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Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
221
Modbus Percentage
Some of the analog read addresses have percentages sent across. The formula used in the percentage
calculation is (actual/max) * 100). The percentage is multiplied by 100 before being sent across the
Modbus to provide up to 2 decimal places, if desired.
Modbus Emergency Shutdown
Two different types of shutdown commands (emergency and controlled) can be issued through Modbus.
The Emergency Shutdown command instantly takes the speed set point and actuator current to zero.
Optionally the 505 can be configured to ignore this Emergency Shutdown command if it is desired to not
allow the unit to be tripped through Modbus.
To avoid an inadvertent trip, the emergency shutdown command from Modbus can be configured to
require a two-step process before a shutdown command is issued. When the shutdown is a two-step
process Boolean write address 0001 starts the shutdown process. An “ESD ACKN ENABLE” feedback
(1:0065) is given and an acknowledgement on address 0002 has to be given within five seconds for the
control to issue a shutdown command.
See Volume 2 for Service mode tunables.
For More Modbus Information
Detailed information on the Modbus protocol is presented in “Reference Guide PI-MBUS-300” published
by AEC Corp./Modicon Inc., formerly Gould Inc. To implement your own source code, you must register
with Modicon. Registration includes purchasing document PI-MBUS-303 and signing a non-disclosure
agreement. You can register to use Modbus at your nearest Modicon field office. To find the office
nearest you, contact Modicon Technical Support at
1-800-468- 5342.