Simatic S7 Sync Module 6ES7960-1AA04-0XA0 6ES79601AA040XA0 6ES796O-1AAO4-0XAO 6ES7 960-1AA04-0XA0

6ES7960-1AA04-0XA0 | SIMATIC S7-400H Synchronization Module V4 — 10m Patch Cable / 210mA / 1.1W / 140×25×53mm / Dual-CPU Redundancy Link

The Component That Makes S7-400H Redundancy Work

The SIMATIC S7-400H is a hot-standby redundant PLC system. Two identical S7-400 CPUs run in parallel — one active (master), one on standby — with identical process images updated simultaneously. If the active CPU fails, the standby takes over without a programme interruption. Field devices, PROFIBUS networks, and the process itself see no gap in control.

The synchronisation module is the hardware that makes this seamless failover possible. One module installs in each of the two S7-400H CPU racks. A patch cable connects the two modules directly — the synchronisation link. Across this link, the two CPUs continuously exchange data: process image updates, timer states, flag values, and data block contents. The standby CPU is always current. When failover occurs, the standby already has the complete process image from the moment before the fault — it takes over from an up-to-date state, not from a reset.

Without the synchronisation module and its link cable, the two CPUs cannot maintain synchronisation. The system cannot operate in redundant mode.

Key Specifications

V4 — Version Context

The 6ES7960-1AA04-0XA0 is Version 4 of the S7-400H synchronisation module. Different hardware versions of the synchronisation module are associated with specific S7-400H CPU hardware generations. The installed CPU modules and their hardware versions determine which synchronisation module version is compatible. The V4 module is used with S7-400H CPUs from the corresponding hardware generation.

The 10m cable limit defines the maximum rack separation distance for this variant. For installations requiring greater separation between the two S7-400H racks, fibre-optic synchronisation modules with extended range must be specified. The 10m copper patch cable variant is appropriate for equipment rooms where both racks occupy the same cabinet row or adjacent positions within a short run.

Application Scenarios

Process plant hot-standby control: Chemical reactor, pipeline station, or power generation control system where a controller fault cannot interrupt process operation. The S7-400H dual-CPU architecture with synchronisation modules provides the failover capability that allows maintenance without planned stops.

Redundant PROFIBUS DP master: Both S7-400H CPUs share a common PROFIBUS DP network. The synchronisation link keeps both CPUs' PROFIBUS data tables identical. On failover, the incoming active CPU continues the DP master polling cycle immediately.

Replacement of failed synchronisation module: A failed synchronisation module prevents redundant operation — the system continues on one CPU but without standby protection. Replacing the 6ES7960-1AA04-0XA0 restores the redundancy link and returns the system to hot-standby mode.

FAQ

Q1: What happens to the S7-400H system if one synchronisation module fails?

If a synchronisation module fails, the two CPUs can no longer exchange synchronisation data. The system runs on the previously active CPU in single-CPU mode — process control continues, but without standby redundancy. A fault diagnostic alarm is generated. Replacing the failed module and re-establishing the synchronisation link restores redundant operation. The S7-400H system does not stop on a synchronisation module fault alone.

Q2: Can S7-400H synchronisation modules with different version numbers be mixed?

No. Both synchronisation modules in a redundant pair must be the same version. Mixing V3 and V4 modules, for example, is not supported. Both modules — one per CPU rack — must carry the same version designation. When replacing one module, confirm the version of the surviving module and order the matching version.

Q3: What patch cable connects the two synchronisation modules?

A standard shielded copper patch cable with the appropriate connector type for the 6ES7960-1AA04-0XA0 connects the two modules. The cable must not exceed 10m. The specific cable order number is documented in the S7-400H system manual. Do not use unshielded cables or extend cable length beyond the 10m limit — this degrades synchronisation signal integrity and can cause synchronisation errors under load.

Q4: Does replacing the synchronisation module require re-initialising the S7-400H system?

After physically replacing the module and reconnecting the patch cable, the S7-400H system performs a synchronisation check — verifying that the two CPUs' memory contents are consistent. If the standby CPU has been in single-CPU isolation for a period, it may require a programme download to resynchronise its memory with the active CPU before redundancy is restored. This procedure is documented in the S7-400H operating manual.

Q5: Is this module used in SIMATIC S7-400 standard (non-redundant) systems?

No. The 6ES7960-1AA04-0XA0 is exclusively for SIMATIC S7-400H redundant systems. It has no function in a standard S7-400 system and cannot be installed in standard S7-400 racks — the S7-400H uses specific H-version CPU modules (such as the CPU 412H, CPU 414H, CPU 417H) that are distinct from standard S7-400 CPUs.