Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 52
Figure 3-3. Speed Probe Rotation Check
Detecting Zero Speed
To enable the 505XT to detect zero speed – an active speed probe signal must be used. The option to
enable this detection feature is found on speed input channel 1. If a second active speed probe is used,
the logic will require that the second probe also detects zero speed. This indication is sent out via Modbus
and can also be used to drive a relay output state.
Figure 3-4. Speed Probe Zero Speed Detect
Manual Speed Override
If the ‘Override MPU Fault’ function is assigned to a contact input, the loss-of- speed detection logic is
overridden as long as this contact is closed; until the maximum time expires. Opening the assigned
contact input, disables the override logic, and re-arms the loss-of-speed detection circuit. Once re-armed,
a system shutdown is executed if the sensed speed drops below the ‘Failed Speed Level’ setting.
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