Siemens PLCs Before SIMATIC S5: Teleperm M, S3, and the S-System

The SIMATIC brand was introduced by Siemens in 1958 and has since gone through four major generations, with SIMATIC S7 representing the current platform. This reference documents the systems that preceded SIMATIC S5, the architectural differences between Teleperm M and the S3/S-system controller families, the practical implications of running legacy Siemens process control hardware today, and the engineered migration paths to PCS 7 and SIMATIC S7. Field engineers maintaining waste incineration lines, power plants, chemical installations, and continuous process facilities will encounter the systems covered here long after their original commissioning dates, and the lifecycle constraints, supported spare parts, and conversion procedures must be understood before any modernization project is scoped.

1. The SIMATIC Generation Timeline (1958 to Present)

Siemens' industrial automation brand is organized into four major hardware generations. Each generation brought distinct programming languages, backplane architectures, and operator interfaces. The historical sequence is critical for migration planning because field wiring, I/O signal conditioning, and rack mechanical formats were never fully backward compatible between generations.

Source for the four-generation classification and 1958 introduction date: SIMATIC - Wikipedia.

2. Pre-SIMATIC Control: The S-System Family

Before SIMATIC branding consolidated the product line, Siemens sold a family of controllers often referred to as the S-system. These were relay-based or early solid-state systems used for machine control in the 1950s and 1960s. The S-system was not a true programmable logic controller in the modern sense; it relied on hard-wired logic implemented with contactor relays, timing relays, and stepping switches. Programs were physical wiring diagrams, and changes required a rewire of the control cabinet.

2.1 S-System Characteristics

• Logic medium: Discrete electromechanical relays, drum programmers, cam timers.
• Programming: None - the program was the wiring diagram.
• Typical applications: Machine tool sequencing, conveyor control, packaging lines, lifts.
• Field I/O: 24 VDC, 110 VAC, 220 VAC discrete; no analog I/O as standard.
• Documentation: Schematic diagrams, terminal lists, relay contact utilization charts.

Engineers maintaining facilities that were originally built with S-system hardware should treat the system as functionally extinct: no Siemens support, no spare parts, and no migration tool. The only viable path forward is a greenfield replacement using a current SIMATIC S7 platform with PROFINET or PROFIBUS distributed I/O.

3. SIMATIC S3 (1970s Compact Modular PLC)

The SIMATIC S3 was Siemens' first widely deployed programmable controller. It used a compact, modular chassis with plug-in function cards and a programming console based on a hand-held keypad or early CRT terminal. The S3 represented Siemens' entry into the PLC market and competed directly with the Allen-Bradley PLC-2 and Modicon 184 families of the same era.

3.1 SIMATIC S3 Hardware Profile

3.2 S3 to S5 Migration Considerations

The S3 CPU uses a different instruction set from the S5. There is no automated cross-compiler shipped with STEP 5. A migration project must reverse-engineer the S3 program into a functional specification, then re-implement in STEP 5 or directly in STEP 7. The I/O wiring side is often reusable with a signal-conditioning adapter or terminal block re-termination, but the S3 backplane format is mechanically incompatible with the S5 or S7 chassis.

4. Teleperm: Siemens' Pre-S5 Process Control System

Teleperm was the designation for Siemens' pre-S5 distributed control system (DCS). It was used primarily in power generation, water treatment, chemical, and waste incineration applications where continuous process control, redundant controllers, and operator-station-driven supervisory control were required. The DCS predates the mainstream acceptance of PLCs in process control and is architecturally distinct from the SIMATIC S-line.

4.1 Teleperm M - The Industrial Standard

Teleperm M was the most widely deployed variant. It was organized around four functional subsystems:

• AS (Automatisierungssystem / Automation System): The process controller; analogous to a PLC CPU but designed for closed-loop regulatory control with hot-standby redundancy.
• OS (Operator Station): The supervisory HMI; cathode ray tube consoles with function keys, trend displays, and alarm annunciation.
• CP (Communication Processor): Gateway modules handling inter-rack communication between AS, OS, and engineering stations.
• IM / IO: Input/Output modules and interface modules, including analog inputs (0/4-20 mA, RTD, thermocouple), analog outputs, and discrete I/O.

Like much of the 1980s electronics, the Teleperm M hardware was engineered for very long service life, with documented installations exceeding 30 years of continuous operation in harsh industrial environments.

4.2 Teleperm M Communication Architecture

The Teleperm M backplane used Siemens' proprietary CS275 bus and later the SIMATIC H1 / PROFIBUS derivatives for inter-rack communication. The OS-AS link was typically redundant, with two CPs operating in parallel and a watchdog-based switchover logic. Field wiring from sensors and actuators terminated on dedicated IM modules, often in cabinets that were physically separate from the controller racks.

5. Why Teleperm M Survived into the 2010s

Several factors contributed to the unusually long service life of Teleperm M systems in the field:

1. Process control inertia. Power plants, refineries, and waste-to-energy lines cannot tolerate sudden control-system failures. A controller swap is a multi-week shutdown event.
2. Proprietary tuning expertise. Many control loops in Teleperm M carry proprietary tuning constants built up over decades. A naive conversion will lose this know-how unless it is meticulously documented.
3. I/O rack longevity. The I/O racks with autonomously running controllers from the early 1980s were still in service decades later because the hardware never failed.
4. Spare parts hoarding. Operators and integrators often stock decommissioned Teleperm M controllers as cold-spare replacements.

However, the practical limits of this approach have now been reached. New Teleperm M components have not been manufactured for many years, repair services are increasingly difficult to source, and any plant safety audit will flag the absence of manufacturer support as a non-conformity.

6. SIMATIC S5 - The Bridge Generation

The SIMATIC S5 series was introduced in 1979 and served as Siemens' flagship PLC line for over four decades. S5 brought STEP 5 programming (STL, LAD, CSF, GRAPH 5) and a modular rack architecture that became the de-facto Siemens standard. The S5 line included:

• S5-90U / S5-95U: Compact, low-cost PLCs for small machines.
• S5-100U: Compact modular with limited I/O expansion.
• S5-115U: Mid-range modular PLC.
• S5-135U / S5-155U: High-end rack PLCs used in process control.
• S5-155H: Fault-tolerant redundant configuration.

The S5 reached end of life on 30 September 2020. Reference: Siemens Support Entry 109776026. After this date, Siemens no longer provides new S5 spare parts, although some third-party rebuilders and legacy stockists continue to offer refurbished components.

6.1 S5 Programming Languages (STEP 5)

7. Migration Path: Teleperm M to PCS 7

Modernization of a Teleperm M installation should be approached as a cutover replacement rather than a code conversion. The two architectures are sufficiently different that an automated translation produces unusable code. The recommended workflow is:

1. Functional specification. Reconstruct the process control narrative from existing Teleperm function block diagrams, OS faceplates, and operating manuals. This is the single most valuable deliverable and the only asset that will transfer to the new system.
2. New control design. Generate fresh CFC / SFC logic in PCS 7 using the standard PCS 7 library (APL - Advanced Process Library). Do not attempt to port Teleperm function blocks directly.
3. Field device audit. Document every sensor, actuator, drive, and valve at the field end. Many field devices can be reused; some will need replacement to match the new I/O module voltage ranges.
4. Cabinet and MCC upgrade. Replace the Teleperm I/O cabinets and the motor control center (MCC) where applicable. The new I/O (ET 200M / ET 200SP) and new motor starters should be installed in parallel with the live system for staged cutover.
5. Operator station build. Reconstruct OS faceplates in PCS 7 WinCC. Use the same process graphic layout as the old OS so that operators transition quickly.
6. Shutdown cutover. Schedule a full plant shutdown, de-energize the Teleperm I/O racks, terminate field wiring to the new I/O, commission, and restart.
7. Tuning and validation. Walk through every loop, valve, and interlock. Re-tune PID constants only if necessary; the original tuning is usually good.

8. Migration Path: SIMATIC S5 to SIMATIC S7 / TIA Portal

The S5-to-S7 transition is more tractable than the Teleperm transition because both are PLC-based. Siemens' official conversion tool (S5 to S7 converter) provides partial automation:

9. Migration Path: SIMATIC S3 to S5 / S7

The S3 is a generation removed from the S5 and there is no supported automated conversion path. Recommended approach:

1. Capture the S3 program as a printout (STL listing) from the PG 605/615/635 programmer.
2. Translate the STL line-by-line into a functional specification.
3. Re-implement in STEP 5 (or directly in STEP 7) using modern programming constructs (structured FB, instance DBs, symbolic addressing).
4. Verify I/O assignments against the original S3 wiring diagram.
5. Re-commission with a controlled loop-by-loop check.

10. Field Engineering: Sourcing Spares for Pre-S5 Systems

Once a system is past its manufacturer-supported life, the spare parts strategy shifts from "call Siemens" to "call a rebuilder." Common field tactics include:

11. Documentation, Cybersecurity, and Regulatory Concerns

Pre-S5 systems are increasingly difficult to defend in a modern cybersecurity audit:

• No authentication. Teleperm M operator stations and S3/S5 programming ports have no concept of user authentication. Anyone with physical access to the programming port has full control.
• No encryption. Field bus traffic on the CS275 / H1 / PROFIBUS layers is unencrypted.
• No patch capability. The firmware is in EPROM and cannot be updated.
• Audit findings. IEC 62443 and similar standards treat unsupported operating systems and controllers as non-conformities. Insurance carriers may refuse cover for plants that rely on unsupported automation hardware.

These factors often accelerate the case for migration, even when the legacy hardware is still functional.

12. Quick Reference: Identifying a Pre-S5 Siemens Controller in the Field

Use the following checklist when auditing a brownfield site for legacy Siemens controllers:

1. Check the manufacturer label on the front of each rack. "SIMATIC S3," "SIMATIC S5," or "Teleperm M" will be printed directly on the chassis.
2. Check the programming port. An S3 uses a 25-pin serial port (PG 605 protocol). An S5 uses the same 25-pin AS511 protocol. Teleperm M uses a proprietary CP link.
3. Check the operator station. Teleperm M OS consoles are large CRT units with function keys; S3/S5 systems do not have an OS - they use pushbutton panels or external HMIs.
4. Check the backplane. S3 and S5 racks use a different connector pitch. Teleperm M racks are physically much larger and use a different mounting footprint.
5. Check the documentation set. The original manuals will be in the site's engineering archive. Look for Teleperm M manuals (gray covers with green stripe), S5 manuals (gray covers with red stripe), or S3 manuals (smaller format, German language).

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