CPU CENTRAL UNIT 6ES7412-3HJ14-0AB0 6ES7 412-3HJ14-0AB0 6ES7412-3HJ14-OABO

Siemens 6ES7412-3HJ14-0AB0 | SIMATIC S7-400H CPU 412-3H — 768KB / 1 MPI/DP + 2 Sync / Entry-Level H-CPU / S7-400H + F/FH

The Entry-Level H-CPU — Where the 412-3H Sits in the S7-400H Range

The CPU 412-3H is the entry point in the S7-400H high-availability CPU family. Understanding its position means understanding what it has and what it does not have relative to the 414H and 417H variants above it.

Memory: 768KB total — 512KB programme and 256KB data. This is the smallest memory allocation in the S7-400H range. The 414-4H doubles this to 1.4MB, and the higher 414-4HM variant reaches 2.8MB.

Communication interfaces: One combined MPI/DP port. The 414H variants add a second dedicated PROFIBUS DP master interface alongside the MPI/DP combined port. For a process plant where one PROFIBUS network is sufficient — one segment covering all instrumentation and drives — the 412-3H's single MPI/DP interface is adequate. For larger plants where two independent PROFIBUS segments would improve network separation and reduce bus loading, the 414H is the appropriate choice.

Redundancy infrastructure: Two synchronisation module interfaces — the same count as the 414H variants. The sync architecture that delivers seamless CPU failover is identical across the H-CPU family. The 412-3H provides the same redundancy quality as the 414H; what it provides less of is memory and communication flexibility.

Key Specifications

How Two CPUs Become One Fault-Tolerant System

The 6ES7412-3HJ14-0AB0 operates only as one unit of a matched pair. Both CPUs run the identical programme simultaneously, processing the same inputs, synchronising their complete state — every output, timer, counter, and memory bit — through the two fibre-optic sync links at every scan cycle. When one CPU develops a fault, the other already holds all current process data and continues execution without interruption. From the field devices' perspective, the PROFIBUS cycles continue unbroken, outputs hold their values, and the process sees nothing.

Two independent sync paths are mandatory. A single sync link would create a single point of failure in the redundancy mechanism itself — one cable fault would destroy the system's ability to synchronise and maintain hot-standby readiness. With two independent paths, a sync link failure generates a maintenance alert without impairing the CPU pair's ability to synchronise until the degraded link is restored.

S7-400F/FH — Redundancy and Certified Safety Together

The CPU 412-3H is certified for S7-400F/FH configurations, which combine hardware redundancy (no unplanned shutdowns from CPU failure) with IEC 61508-certified functional safety (SIL 1/2/3-rated safety instrumented functions via PROFIsafe F-peripherals).

For process industries where both availability and regulatory safety certification are requirements from the same controller, the F/FH configuration addresses both simultaneously.

FAQ

Q1: How does the CPU 412-3H differ from the CPU 414-4H variants?

The 412-3H provides 768KB total memory and one combined MPI/DP interface — no dedicated second PROFIBUS DP port. The 414-4H variants provide 1.4MB or 2.8MB memory and add a second dedicated DP interface for managing two independent PROFIBUS networks. The sync interface count and redundancy architecture are identical. Choose the 412-3H when programme and data fit within 768KB and one PROFIBUS network is sufficient; choose the 414-4H when larger programmes or two DP segments are required.

Q2: How fast is the CPU failover during switchover?

Switchover occurs within the PLC scan cycle — typically in the range of single-digit milliseconds. The standby CPU, having maintained identical programme execution state through continuous synchronisation, resumes execution from exactly where the failed CPU stopped. No process values are lost, no outputs change state due to the switchover, and no manual restart is required.

Q3: Can the S7-400H be maintained while the process is running?

Yes. Hardware redundancy enables online maintenance — replacing a failed CPU module, swapping power supplies, or updating firmware in one rack while the other continues controlling the process. After maintenance, the repaired rack resynchronises automatically with the running rack. This online maintainability eliminates the planned downtime that would otherwise be required for any hardware intervention on a single-CPU system.

Q4: What programming software does the CPU 412-3H require?

STEP 7 Professional V5.x with the S7-REDCONNECT library for redundant communication configuration. TIA Portal does not support the S7-400H CPU family; the current-generation TIA Portal-compatible high-availability platform is the S7-1500H. Existing S7-400H installations must maintain the STEP 7 Classic environment.

Q5: Where is the 6ES7412-3HJ14-0AB0 sourced after discontinuation?

Through Siemens service channels (while stock exists) and the established S7-400H aftermarket — industrial automation spare parts dealers and tested surplus suppliers. Both CPU units of an H-pair must be identical and firmware-matched; source a matched pair when planning replacements. The S7-400H has been widely deployed in critical process infrastructure; the aftermarket holds substantial stock.