Controls Redundant control solution with standard components

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Bachmann Electronic GmbH, Office Bochum Frank Fladerer

FAULHABER Drive Systems

SIMTOS (Seoul International Machine Tool Show)

Redundancy has many forms. In the simplest case, a packaged spare computer is kept in storage and can be put into operation when needed. The maximum variant represents control redundancy, with cycle-synchronous, seamless switching in the event of a malfunction. Bachmann builds the entire redundancy application with standard components, which saves costs.

Redundant controls are considered the pinnacle of automation. They usually require special versions of CPUs, bus couplers, and network components. Bachmann takes a different approach here: with the M200 system, the entire redundancy application is built using standard components. This applies to both hardware components and development tools.

No special requirements are placed on the network infrastructure either. On ships, in road tunnels, or power plants, a network is typically already present. The switches used in these environments already meet the minimum requirements for the industry and support prioritized VLAN. This means that the prerequisites for installing an M200 redundancy are already met.

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Spatially or separately mountable

The two redundant CPUs, which process the same application logic, can be mounted together or separately. When both CPUs are installed in the same cabinet, the operator achieves fault tolerance in the event of a hardware defect. In critical infrastructures, this is usually not sufficient. On ships, for example, planners often go further and lay completely separate networks on the port and starboard sides, with one of the redundant control CPUs operating on each side. This setup not only protects against hardware failure but also against external influences such as water, fire, or partial power outages.

Connected master

Only an additional network connection is required between the redundant CPUs. This facilitates the programming and configuration of both CPUs during commissioning. The service technician can thus reach both CPUs from a central location with his laptop and set up, test, and debug the application. The necessary tools are included in the standard installation of the Bachmann Solution Center.

In operation, the same master-master connection is used for cyclical, clock-synchronized comparison of the process images. The system knows the currently active master ("Primary Master") and automatically ensures that the secondary CPU always provides the same process image. This is the norm because the same control logic produces the same process output image from the same process input image. Only in exceptional cases is a deviation to be expected. This is regarded as an error, displayed, and automatically corrected by the next PLC cycle.

The cycle-synchronous acquisition of signals on the I/O stations and the simultaneous processing on both CPUs is triggered by the Ethernet-based protocol "bluecom," which transmits the data in prioritized VLAN packets. Even if an exact time source such as PTP, SNTP, or GPS is not available, the overall system runs synchronously, right down to the timestamps in the logbooks.

Physically separate networks

The I/O stations with an Ethernet coupler and the M200 I/O modules are connected via two completely separate networks. Single sources of error that could affect both networks ("Single Point of Failure") must be absolutely avoided. For example, both networks must not use the same switch, as its failure would paralyze the entire system.

Both CPUs have crosswise access to the two separate I/O networks. The M200 CPUs are equipped with enough Ethernet ports for this purpose. If these are already used elsewhere, the connection for CPU synchronization can be logically combined with one of the connections for the I/O network on the same cable.

Scada included

Not only can the control and regulation be designed to be highly available from the sensor to the PLC logic, but the operation, monitoring, and archiving of the process can also be executed redundantly with a Bachmann solution: Two autonomously managed Atvise Scada systems with crosswise connection to both CPUs ensure ongoing process control despite network disruptions.

Extended application fields

Redundancy systems have long been the state of the art in critical maritime applications. Applications with redundant control CPUs are also increasing in virtual power plants with redundant feed-in controllers, in infrastructure projects in the water industry, and in wind turbines.

The costs of a failure in a hard-to-reach, normally unmanned facility or even the consequential costs of critical infrastructure failure are high. The M200 system enables the setup of a redundant control solution with standard components, which is a significant advantage compared to other systems on the market.