Chapter 3 - Device Overview
66 3BHS335648 E82 UNITROL 1020 User Manual
output and bring the Main Channel back to Active (and the Redundant back to Standby)
once the failure has been diminished or fixed.
Main Channel Redundant Channel
CAN interface
DO - Changeover
DI - ResetAlarm DI - ResetAlarm
DI - Standby
DI - Standby
Figure 3-14 Typical configuration of Changeover output
Delay on Switch Over output after Power Cycle
Switching back to channel 1 can be done by applying reset Alarm signal to Channel 1
AVR or by power cycling Channel 1.
In order to enable the correct setpoint follow up on Channel 1, the switch over output is
kept active for a defined delay time, configurable by the parameter SWO Startup Hold
Time, which allows Channel 1 to initialize all filters and statuses before taking over control
again.
Switchover hold time is normally only active in case of a power cycle. In terms of Modbus
communication setup, the hold time can also be enabled for regular switch back by setting
the checkbox “SWO Hold Time always active”.
Automatic Logic
Within the DCH SW a configurable logic for forcing the AVR into Manual or automatically
switching off excitation logic is provided.
Automatic forcing logic
OR
Manual ON
Alarm 1 status
Alarm 2 status
Manual ON
Status
AND
Excitation ON
GCB Status
Trip
Excitation ON
Status
AND
Figure 3-15 Automatic forcing logic
DCH Follow-Up
The DCH Follow-up is an automatic function that runs in the Standby channel, following
the actual setpoint used by the Active channel, in order to perform a bumpless transfer
during changeover. The DCH Follow-up is different from Channel Follow-up, which is
used to have bumpless changeover between operating modes within the same Channel
and could also be used on systems without Double Channel software support. For more
information about Channel Follow-up see Chapter 3.4.1.5 - Channel Follow-up.
The DCH Follow-up uses the setpoint information from the Active channel over the CAN
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