System Overview


  • Flexible and scalable hardware solution with redundant controllers, in order to minimize downtimes

  • Various redundancy options:
    - Redundant I/O
    - Redundant fieldbuses

  • Hot-Standby - bumpless changeover without loss of data (< 100ms)

  • Online repair, i.e. replacement of defective components during plant operation

  • Configuration changes, i.e. plant expansions, during operation

  • Simple integration of safety functionality

  • Synchronization of the systems possible up to distances of 10 km

  • The integrated Ethernet interface can be used for the connection of I/O devices or for plant communication

  • Many S7-400H components are also available in a SIPLUS extreme version for extreme environmental conditions, e.g. for use where there is a corrosive atmosphere/condensation.

Advantages and main applications

  • Avoidance of downtimes that a controller failure would cause – specifically in production, energy and water supply, airfield navigation lighting, marshalling yard systems, etc.

  • Avoidance of high restart costs as a consequence of data loss following plant failure – specifically in baggage handling, high-bay storage, tracking & tracing, etc.

  • Protection of plant, workpieces and materials in the event of a plant or machine standstill – specifically in furnaces, the semiconductor industry, or with ships‘ rudders, etc.

  • Safeguarding of operations without supervisory or maintenance personnel – specifically in wastewater treatment plants, tunnels, waterway locks, building systems, etc.


Interfaces of the CPU

All CPUs of the S7-400H series have 5 interfaces:

  • 1 PROFIBUS DP interface

  • 1 MPI/PROFIBUS DP interface

  • 2 interfaces for accommodating the Sync modules

  • 1 PROFINET interface with 2-port switch

Features of H-CPUs

Four new CPUs are available for the SIMATIC S7-400H to suit different performance requirements. Apart from high volumes, the H-CPUs are also characterized by high performance. This is not only visible in a high processing speed, but also in a large communication output.

There are two configuration options for central devices:

  • Design with split module rack

  • Design with two separate module racks if systems have to be completely separate from each other for reasons of availability. The distance between the systems can be up to 10 kilometers (16 miles). 

  • If a particularly high availability is required, you can use two redundant power supplies.

User-friendly and efficient engineering

Redundancy is an integrated system function of the S7-400H.
Programming of the SIMATIC S7-400H is analogous to a standard system.
All STEP 7 programming languages are supported.

Existing standard system programs can easily be ported to a redundant system and vice versa. When the program is loaded, it is automatically transferred to the two redundant CPUs.

The redundancy-specific functions and configurations are parameterized with STEP 7.

High availability and safety in one system

S7-400FH combines high availability and safety technology in a single automation system.

The architecture of SIMATIC S7-400FH tolerates faults while maintaining safety (see PROFIsafe).

The system is TÜV certified and complies with all relevant standards for production and process automation.

Highly available HMI systems

As far as the availability of HMI systems is concerned, Siemens offers scalable solutions which can seamlessly be integrated into the architecture  of highly available systems. While fault-tolerant controllers minimize downtimes of machines and plants highly available HMI systems ensure their operability at any time. The key to this is the capability to support redundant architectures and communication channels


Configuration of the central controllers

The central devices can be configured in two different ways:

When the subunits have to be completely separated from each other for availability reasons, it is appropriate to use two standard racks (UR1 and UR2). Each rack accommodates one CPU and one power supply (PS). If extremely high availability is required, two redundant power supply modules can be used. The distance between the two racks can be up to 10 km.

Two CPUs, each with either a single or a redundant power supply, are plugged into the UR2-H rack with a segmented backplane bus. This enables an extremely compact configuration.

I/O connection

One-way (left) or switched (right) I/O interface via PROFIBUS

The I/Os can be connected flexibly via PROFIBUS and PROFINET. PROFIBUS and PROFINET configurations can be combined with one another.

PROFIBUS can provide a one-way interface (normal availability), a single-channel connection (normal availability) or a switched interface (increased availability).

One-way (left) or system-redundant (right) I/O interface via PROFINET

PROFINET provides a one-way interface (normal availability) or a system-redundant interface via open ring. Availability in the open ring increases when devices that support PROFINET IO system redundancy are connected, such as the SIMATIC ET200M distributed I/O.


Hochverfügbare Kommunikation

Fault-tolerant communication for redundant connections is already integrated into the SIMATIC S7-400H. In the event of a fault, the fault-tolerant communication link can take over automatically and invisibly to the user. When the I/O is connected via PROFIBUS, the internal PROFINET interface can be used for communication.