SIMATIC S7-1500 R/H for redundancy and high availability

Avoid plant downtime with redundant automation solutions using SIMATIC S7-1500 CPUs

Avoid plant downtime with redundant automation solutions

Maximum plant availability is essential – but how can you achieve this goal? The redundant and high-availability SIMATIC S7-1500 R/H CPU is the answer. A backup CPU synchronized with the primary CPU ensures that no data is lost in the switchover. And best of all, synchronization and project consistency are a system function. Which means that you don’t need special knowledge to use a SIMATIC S7-1500 R/H CPU: The engineering is performed in TIA Portal as usual.

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Redundancy at a glance

How redundant solutions can improve plant availability

Redundancy is important for plant availability. But why, exactly, and what does it involve? Discover how redundant systems can solve several potential problems with plant operation and maintenance.

Redundant systems reduce costs and increase productivity

Machine and plant downtime nearly always means production outages. In the worst case, an unplanned plant outage can damage the product or the machinery, which incurs more costs. Redundant systems can prevent outages in many cases, they’re easier to maintain than application-based solutions, and they may also meet legal requirements. But if a CPU outage occurs, production can continue because the backup CPU takes over seamlessly. And because service technicians aren’t always on-site, you have more time to schedule service work.

Safety, security, availability – the key elements

In addition to availability, safety and security are two more key factors in plant operation, although they differ greatly in terms of their focus and effects. Safety protects people and machines if a fault occurs, and it puts the plant units in question in a safe state: I other words, it brings them to a stop in most cases. Security prevents attacks from outside like cyber attacks or sabotage and so helps maintain availability. Redundant solutions enable what’s known as “hot standby” to ensure that the plant can continue to run in the event of an outage or other unforeseen events. This involves linking redundant CPU pairs together via PROFINET. High-availability CPU pairs are connected using synchronization modules and fiber-optic cable, which shortens the switchover time for H-CPUs by about a factor of six to 50 ms. The IO periphery is connected to the primary and backup CPU as a switched S1 or S2 device via the PROFINET ring and the media redundancy protocol (MRP).

System comparison

Redundant CPUs at a glance

Discover the similarities and differences between the redundant SIMATIC S7-1500 R CPU and the high-availability SIMATIC S7-1500 H CPU in the technical specifications.
Redundant CPU


High-availability CPU


CPU type
1513R CPU/1515R CPU as a pair
1517H CPU/1518HF CPU as a pair
via PROFINET ring (MRP)/max. 100 m
via synchronization modules/fiber-optic cable, max. ~6.2 miles
Hot standby
Yes, fail-over time approx. 300 ms
Yes, fail-over time approx. 50 ms
IO systems
SIMATIC 200SP and ET 200MP
Connection type
S1 and S2 devices via PROFINET
S1 and S2 devices via PROFINET
Technical specifications for SIMATIC S7-1500 R/H CPUs

Overview of additional technical details on the SIMATIC S7-1500 R/H CPUs

All of the technical specifications for the redundant and high-availability CPUs are available in the Siemens Industry Mall. You can also use the TIA Selection Tool to configure the devices identically.

Potential applications

Discover the many applications for redundant systems

Many applications require maximum availability. What structures are recommended for different areas of application? We’ll show you some typical examples drawn from practice.

Hot standby: To ensure that nothing happens when a CPU fails

Redundant CPUs are synchronized via PROFINET and are suitable for less time-critical applications where CPU availability combined with spatial proximity is very important. High-availability CPUs support applications where a short switchover time and a greater distance are also important, in addition to availability. This is where dedicated synchronization modules and fiber-optic cables come in. The primary CPU is programmed just like a standard CPU: The backup CPU is automatically fed the same program by the system and synchronously monitors the primary CPU in operation.

Avoid financial losses

Outages in baggage handling systems at airports are usually annoying, but they’re also costly if they result in delays in flight schedules. In warehouses and other logistics areas, outages can cause the supply chain to break down, which will quickly lead to significant financial losses because the next processes in the sequence will also be brought to a stop. The consequential costs will usually exceed the cost of investing in redundant systems many times over. This is where a decentralized IO system structure is recommended, with an active backplane bus in addition to a SIMATIC S7-1500 R/H CPU for maximum availability.

Reliable operation must always be assured

For safety reasons, systems in tunnels such as traffic control, ventilation, smoke extraction, and lighting must always be fail-safe. High-availability SIMATIC S7-1500 H CPUs can be synchronized over up to about 6.2 miles. This is a huge advantage in tunnels, which can often reach lengths of several kilometers, and it also makes it easier to construct redundant systems. If the safety requirements increase – for legal reasons, for example – the CPUs can be expanded by adding new fail-safe software blocks to provide optimal investment protection.

When constant air-conditioning is essential

In many areas it’s essential to have an air-conditioned atmosphere, even outside regular work hours. Outages that affect equipment for ventilation or air treatment – including humidification and heating – must therefore be reliably prevented. But if a fault occurs, it’s vital to rectify it as soon as possible. This is where it’s practical to have a redundant solution that uses SIMATIC S7-1500 R CPU in place.

Decentralized structure for decentralized devices

Pumps for water treatment are often distributed across multiple sedimentation tanks – along with the IOs. Because the treatment process is relatively slow, it’s not essential for the CPUs to be high-availability. A decentralized structure for the IO system ensures that a short-term outage affecting a single station will remains non-critical and the system can continue operating. If a higher level of availability is also required at the CPU end, SIMATIC S7-1500 R CPUs will do the job – depending on the quantity framework, SIMATIC S7-1500 H CPUs are also used.

Central CPU structure

Minimal space requirements and high cost pressures are important factors in mechanical engineering. Machines are normally switched off at the end of a shift and aren’t left to run unsupervised. That’s why these cases usually involve a central structure with just a single CPU. If individual sensors or IO channels fail, it’s easy to bypass them thanks to their deliberately redundant configuration.


Redundant SIMATIC systems in practical use

Learn how our customers overcame the challenges they faced using redundant and high-availability SIMATIC S7-1500 R/H CPUs.


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Let our experts advise you on the configuration that’s right for your application and the SIMATIC-based redundancy system that’s most appropriate. Find your closest contact fast using our contact database.