Siemens S7-1500 Redundancy Configurations and Cases

Configuration Overview

First, the 1500 series PLC models that currently support redundancy are:

• CPU 1517H-3PN, order number: 6ES7517-3HP00-0AB0
• CPU 1515R-2PN, order number: 6ES7515-2RM00-0AB0
• CPU 1513R-1PN, order number: 6ES7513-1RL00-0AB0

One more point to remember: a PROFINET ring must be used in all configuration modes.

Within S7-1500R/H systems, the following components can be redundant:

• R/H CPU
• synchronization interface
• media in the PROFINET ring

This configuration section describes available configuration options and their advantages.

S7-1500R/H with IO Devices on a PROFINET Ring

Advantages:

• IO devices using S2 system redundancy can exchange process data uninterrupted with the S7-1500R/H redundant system when a CPU fails.
• If a cable break occurs at any position in the PROFINET ring, the redundant system can continue to operate.

S7-1500R configuration

S7-1500H configuration

Using Switches and Linear Topology with S7-1500R/H

Advantages:

• Switches can be used to add other linear topologies to the PROFINET ring. Unlike the PROFINET ring, linear topologies are not redundant.
• PROFINET IO devices can be located in the PROFINET ring or separated via switches.

S7-1500R configuration

S7-1500H configuration

Case Analysis

The following examples show possible redundancy scenarios for different configuration modes. Redundancy does not limit the process. In these examples, the redundancy system supports fault-tolerant operation.

Main CPU Failure

Event sequence:

1. The redundant system's main CPU fails while in the RUN-Redundant system state.
2. The redundant system switches to the backup CPU. The backup CPU becomes the new main CPU. The redundant system changes to the RUN-Solo system state.
3. The new main CPU exchanges process data with the IO devices.

Notes:

Standard IO devices are temporarily isolated when the main CPU fails.

If the main CPU fails, standard IO devices are temporarily isolated from the S7-1500R/H redundancy system. During this period, configured substitute-value behavior applies to the modules of the standard IO devices.

The new main CPU reestablishes the connection to the standard IO devices. After a short time, the main CPU resumes process data exchange with the standard IO devices.

System redundancy is limited. This limitation has no impact on the process.

If another system component or another network segment fails, the S7-1500R/H redundancy system may fail.

Diagnostics:

System state, operating state, and error display after the main-backup switch:

• Redundant system -> RUN-Solo system state
• Main CPU (previously the backup CPU) -> RUN operating state
• MAINT LED indicator -> lit yellow: R/H system is not in RUN-Redundant system state. No partner CPU found in the redundant system. PROFINET ring is disconnected.
• Backup CPU (previously the main CPU) -> fault

For detailed diagnostic information, check the diagnostic buffer.

Solution: Replace the faulty CPU.

Backup CPU Failure

Event sequence:

1. The redundant system's backup CPU fails while in the RUN-Redundant system state.
2. The redundant system switches to the RUN-Solo system state.
3. The main CPU continues to exchange process data with IO devices and standard IO devices.
4. System redundancy is limited. This limitation has no impact on the process.

If another system component or another network segment fails, the S7-1500R/H redundancy system may fail.

Diagnostics:

System state, operating state, and error display after the main-backup switch:

• Redundant system -> RUN-Solo system state
• Main CPU -> RUN operating state
• MAINT LED indicator -> lit yellow: R/H system is not in RUN-Redundant system state. No partner CPU found in the redundant system. PROFINET ring is disconnected.
• Backup CPU -> fault

For detailed diagnostic information, check the diagnostic buffer.

Solution: Replace the faulty CPU.

PROFINET Cable Fault in the PROFINET Ring

Event sequence:

1. A fault or disconnection of a PROFINET cable causes the PROFINET ring of the redundant system to be broken.
2. The redundant system remains in the RUN-Redundant system state. The main and backup CPUs remain in the RUN-Redundant operating state.
3. The redundant system reconnects via the alternate connection to the backup CPU. This allows the redundant system to regain access to all IO devices in the PROFINET ring.

System redundancy is limited. This limitation has no impact on the process.

If another system component or another network segment fails, the S7-1500R/H redundancy system may fail.

If the PROFINET cable also fails at another point, IO devices in the PROFINET ring may fail, depending on the location of the break.

Diagnostics:

System state, operating state, and error display after the PROFINET cable fault:

• Redundant system -> RUN-Redundant system state
• Main CPU -> RUN-Redundant operating state
• MAINT LED indicator -> lit yellow: PROFINET ring is disconnected. Only one redundant connection remains in the redundant system.
• Backup CPU -> RUN-Redundant operating state
• MAINT LED indicator -> lit yellow: PROFINET ring is disconnected. Only one redundant connection remains in the redundant system.

Warning: S7-1500R redundancy system failure

If, in addition to the PROFINET cable, the main CPU also fails, the backup CPU will switch to the STOP operating state.

For detailed diagnostic information, check the diagnostic buffer.

Solution: Replace the faulty PROFINET cable or reconnect the disconnected PROFINET cable.