User manual

Toolbox 32 User Manual 1.47d www.cse-semaphore.com/mykingfisher
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211
Secondary RTU Takes Control
For this example, the master RTUs use the same ladder logic and are identical except for their RTU address.
Edits only need to be made to the primary RTU's ladder logic and then a copy of the ladder logic is used for
the secondary RTU.
Primary RTU1 starts up in primary listen mode and then sends a message to secondary RTU2 to make sure
it is in secondary listen mode (when RTU2 receives any message from RTU1 it changes to secondary listen
mode). If the message is not successful, the primary RTU will keep trying to send a message every minute to
secondary RTU2. If the message is successful or a Force Control command is received, primary RTU1
changes to primary control mode and begins polling RTU3 and RTU4 every 15 minutes. Secondary RTU2
starts up in Secondary Listen mode and if it has not heard from primary RTU1 for 35 minutes (waits a bit
longer than 2 polls), it changes to Secondary Control and begins responding to any messages for primary
RTU1 and carrying out polling. When secondary RTU2 is in control mode, it checks if RTU1 is OK at the start
of each system poll. If this message is successful, secondary RTU2 immediately reverts to secondary listen
mode and will not carry out the system poll.
SCADA Software
The same SCADA software configuration can be used with both the primary and secondary RTUs. The RTU
will respond with either its own local data or its network data depending on what RTU address is requested
by the SCADA software.
Data common to both masters is read from the primary RTU address (eg. 1). This could include comms
success and fail counters for each outstation RTU (stored in local registers in RTU1). When the primary
master is active, it updates these counters after any comms successes or fails and then sends these counter
values to the secondary master (RTU2). While the secondary master is in listen mode, it overwrites its own
comms counters (also stored in local registers) with the network data from RTU1.
If the primary master fails and the secondary master becomes active, the secondary master begins
managing its own comms counters. These counters already contain the values last received from RTU1.
While the secondary master RTU2 is active, it copies the new value of its own comms counters over the old
comms counters stored in network registers for RTU1. This allows the secondary master SCADA software to
display the correct value for the comms counters at all times.
Note: some SCADA software drivers (eg. Modbus) allow data to be read from RTU address 0. All RTUs will
respond to this address which simplifies some of the data management.
Secondary RTU2
Primary RTU1
RTU2 in
listen
mode
Comms counters
read from RTU1
local registers
RTU2 in
control
mode
Local Data
Network
Registers
Local Data
Comms counters
read from RTU1
network registers
RTU1 lo
cal registers
are transferred to
network registers in
RTU2
Network
Registers
SCADA
SCADA
Figure: Managing Common Registers In The Primary And Secondary RTUs