Application Note 14
Dual Communications
The
upgrade for dual communications provides increased system integrity by
ensuring that the failure of a communication path can be tolerated without
compromising the system. It provides dual redundancy, whereby both
paths are used all the time, so failure of either will be immediately
detected, but will not stop the system functioning. This offers
obvious advantages over main/standby operation, where failure of the
standby path would not be detected until the system switches to it.
The feature can be used to give dual communications by radio and leased
line, for additional security. It can also be used to configure a
system to operate on two radio channels to give increased immunity to
failure due to radio interference.
The
functionality can be applied to any Micro_Link units by adding a Comms
Expansion module and installing a firmware upgrade (it is not currently
available for use on Nano_Link). If the user want to access the
relevant alarm flags he will also need to upgrade the configuration
software on his computer to DCD Version 2.17 or later.
The
Comms Expansion module connects via the I/O_Link bus in the same way as
any other expansion modules. Furthermore, it uses the same
mechanical construction.
Any
combination of communication media can be used (except GSM). For
example, the Micro_Link could be fitted with a radio and the Comms
Expansion module with a leased line modem.
When the upgrade is applied, the Micro_Link will transmit on both paths, and listen for incoming messages on both paths. If it fails to receive messages on one path it will generate a ‘Dual Comms Fail’ alarm, but keep functioning on the other path. It will simultaneously raise an ‘Expansion Comms Fail’ alarm if the fault is with the comms expansion module. This applies equally to Micro_Link’s configured as outstations, repeaters or base-stations.