User manual
Toolbox 32 User Manual 1.47d www.cse-semaphore.com/mykingfisher
Page
204
Appendix - Redundancy
Redundancy allows an RTU to cope with equipment failures and continue operating normally. The RTU
shown below has redundant power supplies, CPUs and communications. The setup of these components is
detailed in the following sections. Another way of coping with equipment failures is to have two separate
RTUs as detailed in the topic Redundant RTUs. Each RTU can also be monitored and controlled by two or
more PCs running SCADA software as detailed in the topic Redundant PCs.
Redundant Power Supply
Power Supply
Duty CPU (even slot address)
Redundant CPU (odd
slot address)
Standby LAN
Duty LAN
RADIO
RADIO
CP11
CP11
PS11
PS11
Standby Radio
Duty Radio
Redundant CPUs
An RTU can have two redundant CP-10/11/21 modules with one CPU in duty mode and one CPU in standby
mode. If the duty CPU fails or is removed, the standby CPU takes over full control of the RTU.
A system with redundant CPUs must always have one CPU in an odd slot address and one CPU in an even
slot address (note: the CPUs do not have to be physically next to each other on the backplane). When the
system starts up, the CPU in the even slot will become the duty and the CPU in the odd slot will become the
standby (indicated by the L2 LED flashing).
The duty CPU does all the same things as a single CPU system and also scans the standby CPU to check if
it is still in standby mode and then updates the standby CPU's registers with its own values.
Updating The Standby CPU
• Digital and analog hardware registers are updated whenever a value is written to a digital or analog
output module.
• Network data is updated whenever a new data message is received by the duty CPU.
• Local registers and event logs are updated every couple of seconds.
• The real time clock is synchronized every hour and whenever the duty clock is written to.
• Network data, timer registers, system registers, inactivity parameters, network configuration variables
and most port configuration variables are checked a couple of times per minute and any differences are
updated.
• Ladder logic, telephone numbers, Ethernet parameters (eg. IP address), PSTN parameters, paging
parameters and TMR parameters are not updated.