The construction of high-availability systems by using controller redundancy is also very attractive and economical for small applications. APROL supports redundancy on all levels; operator bus and process bus, as well as runtime server and controller can be set up redundantly.
The CPU redundancy switchover is in the range of only 1 to 2 task cycles on the I/O bus, and is therefore completed within a few milliseconds.
When a controller is exchanged during operation, the controller operating system and control application are updated automatically and then the real-time data is synchronized.
To configure a redundant controller, the user simply declares it as such. This can also be done retrospectively.
Apart from the real-time data, the runtime server also contains the trend and alarm systems as well as the report server. Redundancy support also includes execution of the control computer tasks. In case the computer with process control fails, there is an automatic take-over of the jobs by the redundancy partner (master/slave). The recording gaps which occur in the historical archive during a failure standstill are automatically compensated for by the system.
The controller without control of the process monitors all data traffic on the POWERLINK fieldbus – including the synchronization signal of the controller with control of the process – in order to be able to react without delay within one network cycle. Data for synchronizing the two controllers is exchanged continuously over a redundancy link, which is based on Gigabit Ethernet. All of the hardware components come from the standard X20 product portfolio.
With controller redundancy, one controller controls the process while another stands by in inactive mode. Continuous monitoring ensures that, if necessary, the inactive controller can take over all of the active controller's functions in a completely bumpless manner.
Bonding can be used to increase the availability of the operator bus and process bus. This allows two independent Ethernet interfaces on the nodes to be used without doubling the communication load.