Legacy PLC Emulators vs. Full Migration: Pros and Cons

PLC emulators and adapter modules physically replace the old CPU but run the original program in emulation. They avoid program conversion — you keep the S5 code running on modern hardware. This sounds ideal, but it solves only part of the problem. This article compares emulation against full migration honestly.

What PLC Emulators Do#

An emulator is a hardware module that fits into the existing S5 rack (or replaces it) and executes the S5 program without conversion. The emulator translates S5 machine code to its internal processor in real time. Popular products include VIPA SPEED7, Helmholz S7-mEC, and IBH S5 to S7.

Comparison Table#

When Emulation Makes Sense#

As a bridge solution (1–3 years):

• Buy time while planning a proper migration
• The S5 CPU has failed and a replacement is not available
• Budget for full migration is not yet approved
• The machine is scheduled for decommission in 2–3 years

For non-critical, stable systems:

• The program never changes
• No integration with modern systems needed
• The machine runs independently (no network, no HMI updates)

When Emulation Does NOT Make Sense#

For long-term operation (5+ years):

• You are dependent on a niche emulator vendor instead of Siemens
• STEP 5 is still required for any program change (DOS/Windows XP)
• No access to modern features (OPC UA, web diagnostics, cloud connectivity)
• The code remains undocumented — the knowledge problem is not solved

For safety-critical systems:

• Emulators typically do not have safety certifications (SIL/PL)
• Safety validation must be redone regardless

For interconnected systems:

• If the machine needs to communicate with modern systems (MES, ERP, other S7-1500s)
• Emulators typically support PROFIBUS but limited PROFINET/OPC UA

The Hidden Cost of Emulation#

Emulation looks cheaper initially: €5,000 vs. €30,000. But over 5 years:

The 5-year cost difference is only €6,500 — but the full migration gives you documented code, modern features, and standard Siemens support. The emulation gives you the same undocumented S5 code on a different CPU.

PLCcheck Pro: Making Full Migration Affordable#

The main argument for emulation is "migration is too expensive and complex." PLCcheck Pro changes that calculation:

• Code analysis in minutes instead of days of manual reading
• Automatic documentation eliminates the biggest migration cost block
• S7 equivalent generation reduces engineering time by 30–50%

With PLCcheck Pro, the cost gap between emulation and migration shrinks significantly — and the migration delivers far more long-term value.

Analyze your S5 code before deciding →

Frequently Asked Questions#

Can I use an emulator now and migrate later?

Yes, this is a valid strategy. The emulator keeps the machine running while you plan and budget for migration. Just make sure "later" has a date.

Does the emulator run my S5 program exactly the same?

Mostly yes, but timing behavior can differ slightly. Analog processing, interrupt handling, and communication timing may need verification.

What if the emulator vendor goes out of business?

This is the key risk. You exchange dependency on S5 spare parts for dependency on a niche vendor. At least with S5 spare parts, multiple third-party suppliers exist.

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Maintained by PLCcheck.ai. Last update: March 2026. Not affiliated with Siemens AG.