Evaluating PROFINET System Redundancy (S2) and Power Supply Architectures for ET 200M in SIMATIC PCS 7

In SIMATIC PCS 7 architectures utilizing ET 200M distributed I/O stations, PROFINET connectivity is implemented using single IM 153-4 HF interface modules operating in PROFINET System Redundancy (S2) mode, rather than mounting dual interface modules on an active backplane bus as done with PROFIBUS DP IM 153-2. While PROFIBUS DP supports dual redundant IM 153-2 modules on a shared active bus module (6ES7195-7HD10-0XA0), ET 200M PROFINET stations cannot host two IM 153-4 modules in a single rack. Power supply redundancy for ET 200M is achieved externally using dual SITOP power units coupled through redundancy modules, as no monolithic redundant PS 307 rack power supply exists.

PROFINET S2 System Redundancy vs PROFIBUS DP Dual-IM Architecture

Historically, SIMATIC PCS 7 plants established high-availability field connections using PROFIBUS DP, where an ET 200M modular station housed two IM 153-2 interface modules (6ES7153-2BA10-0XB0) mounted onto an active bus module (6ES7195-7HD10-0XA0). Each IM connected to one line of an S7-400H redundant controller pair. This configuration provided complete line, transceiver, and interface module redundancy.

With the advent of PROFINET IO in PCS 7 (starting in PCS 7 V8.1/V8.2), communication shifted to Ethernet-based industrial networks. PROFINET defines distinct redundancy topologies under PI guidelines:
- System Redundancy (S2): A single PROFINET interface module establishes logical Application Relations (ARs) to both CPU 410-5H / S7-400H controllers over a ring network managed by Media Redundancy Protocol (MRP). One AR is primary (data exchange), while the backup AR remains active for bumpless failover.
- System Redundancy (R1): A distributed I/O station contains two separate interface modules, each connected to an independent PROFINET network. R1 redundancy is supported in modern ET 200SP HA systems using dual IM 155-6 PN HA modules, but is physically and functionally unsupported on ET 200M racks.

ET 200M Hardware Constraints with IM 153-4 HF

Engineers designing ET 200M stations with the PROFINET interface module IM 153-4 PN HF (6ES7153-4BA00-0XB0) must account for specific physical hardware limits:

Single Module per Rack: The ET 200M backplane bus architecture does not support mounting two IM 153-4 modules on a single rack. There is no active PROFINET bus module equivalent to the dual-slot 6ES7195-7HD10-0XA0.
S2 Logical Redundancy Only: The IM 153-4 PN HF provides S2 redundancy to redundant S7-400H / CPU 410-5H controllers. If the physical IM 153-4 module fails, the entire ET 200M station loses communication.
Ring Network Topology: Redundancy against physical cable breakage is provided by wiring the two integrated RJ45 ports of the IM 153-4 HF into an MRP ring closed by SCALANCE X switches or the integrated PN ports of the CPU 410-5H.

Implementing Redundant 24V DC Power for ET 200M Stations

Unlike the S7-400 central rack—which supports dual redundant PS 407 power supplies (6ES7407-0RA02-0AA0) seated in the same chassis—the ET 200M line has no native dual-slot redundant power supply module. The standard SIMATIC S7-300 / ET 200M power supply (PS 307, e.g., 6ES7307-1EA01-0AA0) is a single, non-redundant unit.

To achieve robust power redundancy for ET 200M stations:
- External Redundant SITOP Configuration: Deploy two identical 24V DC switch-mode power supplies (e.g., SITOP PSU8200 6EP3436-8SB00-0AY0).
- Decoupling Module: Route the 24V outputs of both supplies through a SITOP redundancy module (e.g., SITOP PSE202U 6EP1961-3BA21 or SITOP RED1200 6EP4346-7RB00-0AX0). The redundancy module isolates short circuits in either power supply using Schottky diodes or active MOSFET decoupling.
- Power Distribution: Feed the decoupled 24V DC output simultaneously to the IM 153-4 / IM 153-2 power terminals and the front connectors of digital and analog I/O modules.

Redundancy Topology Comparison for Distributed I-O

The following table compares redundancy levels across distributed I/O families in SIMATIC PCS 7:

Distributed I/O FamilyInterface ModuleFieldbus ProtocolSystem Redundancy LevelInterface Redundancy (Module Failure)Cable Failure ProtectionET 200M Redundant2x IM 153-2 High Feature (6ES7153-2BA10-0XB0)PROFIBUS DPDual Master / Flying RedundancyFull (Dual IMs on active backplane)Dual independent PROFIBUS linesET 200M PROFINET1x IM 153-4 PN High Feature (6ES7153-4BA00-0XB0)PROFINET IOS2 RedundancyNone (Single IM failure drops rack)MRP Ring TopologyET 200SP HA2x IM 155-6 PN HA (6DL1155-6AU00-0PM0)PROFINET IOR1 RedundancyFull (Dual IMs on terminal block)Dual MRP rings / Separate subnetsET 200iSP2x IM 152-1 (6ES7152-1AA00-0AB0)PROFIBUS DP (IS)Flying RedundancyFull (Dual IMs for hazardous areas)Dual intrinsic safety DP lines

Note: For new plant designs requiring both PROFINET and physical interface module redundancy, Siemens specifies ET 200SP HA rather than legacy ET 200M.

Verification

Verify ET 200M PROFINET and power redundancy through these operational checks:
1. In HW Config, verify that IM 153-4 HF is connected to both redundant CPU 410-5H controllers with S2 redundancy active and MRP role set to Client.
2. In runtime, disconnect the primary PROFINET cable to the IM 153-4 HF and verify that the MRP ring reconfigures within 200 ms without dropping I/O communication.
3. Switch off the primary SITOP power supply feeding the redundancy module and verify with a multimeter that 24V DC remains uninterrupted across the ET 200M backplane.

Limitations and Operational Precautions

Key architectural limitations must be observed when planning ET 200M stations:
- The IM 153-4 PN HF does not support R1 redundancy; a physical electronics failure on the IM halts communication to all modules on that rack.
- Do not mix PROFIBUS active bus modules (6ES7195-7HD10-0XA0) with PROFINET IM 153-4 stations.
- Always monitor the signaling contacts of the external SITOP redundancy module via digital inputs in CFC to trigger an alarm when one power supply fails before total loss of station power occurs.

Engineer FAQ

Can I use two IM 153-4 modules on one ET 200M station?

No. The ET 200M backplane hardware does not accommodate dual PROFINET interface modules. Redundancy at the interface module level on PROFINET requires the ET 200SP HA platform.

What happens if an MRP ring breaks on an ET 200M PROFINET system?

The redundancy manager (SCALANCE switch or CPU) detects the link break and transitions from ring mode to linear line mode in under 200 ms, maintaining uninterrupted process data flow.

Is there an internal redundant power supply for ET 200M like the PS 407?

No. ET 200M uses standard single-width PS 307 power modules. High-reliability installations must use external SITOP power units with diode or MOSFET redundancy modules.