Where SISTEMA fits in the process
By this point in the series you've completed your ISO 12100 risk assessment, identified your required Performance Levels, and designed your safety circuits. SISTEMA is the step that closes the loop — it validates that the circuits you've designed actually achieve the Performance Level your risk assessment demands.
Think of it as a building block calculator. You enter each component of each safety circuit into SISTEMA — the E-stop button, the safety relay, the contactors, the door interlock — and it assesses each one as a block in the system. Once all the blocks are entered, SISTEMA tells you whether the combined circuit achieves the required PL. If it does, your safety circuits are validated and approved safe to wire.
SISTEMA automates the Performance Level calculation defined in ISO 13849-1. Without it, you'd need to manually calculate MTTFd, DCavg and CCF for every component in every safety circuit — a process that involves complex formulae and extensive reference tables. SISTEMA does all of that automatically once you've entered the component data.
What is SISTEMA?
SISTEMA stands for Safety Integrity Software Tool for the Evaluation of Machine Applications. It was developed by the IFA — the Institute for Occupational Safety and Health of the German Social Accident Insurance (Deutsche Gesetzliche Unfallversicherung, DGUV). It is free to download, free to use for commercial purposes, and free to distribute.
It is the industry standard tool for validating safety circuits against ISO 13849-1 and is accepted by certification bodies and notified bodies across Europe. If your Technical File needs to demonstrate that your safety functions achieve their required Performance Level, a SISTEMA report is how you demonstrate it.
Download SISTEMA free from the IFA websiteUnderstanding Performance Levels
Before you can use SISTEMA you need to understand what you're validating against. ISO 13849-1 defines five Performance Levels — PLa through PLe — representing increasing levels of safety integrity:
| Performance Level | PFHd (probability of dangerous failure per hour) | Typical application in robot cells |
|---|---|---|
| PLa | ≥ 10⁻⁵ to < 10⁻⁴ | Low risk — rarely applicable to robot cells |
| PLb | ≥ 3×10⁻⁶ to < 10⁻⁵ | Low-medium risk functions |
| PLc | ≥ 10⁻⁶ to < 3×10⁻⁶ | Medium risk functions |
| PLd | ≥ 10⁻⁷ to < 10⁻⁶ | High risk — most robot cell safety functions including E-stop, guard interlocks, enabling device |
| PLe | ≥ 10⁻⁸ to < 10⁻⁷ | Highest risk — collaborative robot speed and force limiting, some specialist applications |
For most industrial robot cells, your risk assessment will determine that your primary safety functions — E-stop, guard door interlocks, enabling device for teach mode — require PLd. This is the level your SISTEMA validation needs to confirm is achieved.
What you enter into SISTEMA
SISTEMA structures each safety function as a hierarchy of subsystems, channels and blocks. For each component in the safety circuit you enter:
| Parameter | What it means | Where you get it |
|---|---|---|
| Category | The architecture of the safety circuit — single channel (Cat B/1) or redundant dual channel (Cat 2/3/4). Most robot cell safety functions will be Category 3 or 4. | Your safety circuit design from Part 3 |
| MTTFd | Mean Time to Dangerous Failure — a reliability figure for each component expressed in years. Higher is better. | Component datasheet or manufacturer's SISTEMA library |
| DCavg | Diagnostic Coverage — how well the system detects its own faults. Expressed as a percentage. | Determined by the circuit architecture and any self-monitoring features |
| CCF | Common Cause Failure measures — steps taken to prevent a single event causing failure of both channels in a redundant system. | Checklist within SISTEMA based on your design measures |
The good news is that most major safety component manufacturers — Pilz, Sick, Schmersal, Omron, Rockwell — provide SISTEMA libraries for their products. This means the MTTFd and DC values for their components are pre-loaded and you don't need to find them manually. Download the library file from the manufacturer's website and import it into SISTEMA.
The practical approach — from experience
Honestly, SISTEMA is not the most intuitive software you'll ever use. The learning curve is real and the first time you use it will take significantly longer than you expect.
We figured it out once, validated our first set of safety circuits, and then used the same circuits — with the same components — for every cell we built after that. The key is over-specifying your components from the start. If your E-stop button, safety relay and contactors are specified well above the minimum requirement for PLd, the same SISTEMA project validates every cell you build that uses those components. You're not starting from scratch each time — you're confirming the same validated design is in place.
This is the most practical advice we can give: don't try to achieve exactly PLd with components that just scrape through. Specify quality components with high MTTFd values, use a proven Category 3 or 4 architecture, and build a validated SISTEMA project you can reuse. The time investment is front-loaded but the payoff is that every subsequent cell takes minutes rather than days to validate.
Component selection tip
Stick to manufacturers who provide SISTEMA libraries — Pilz, Sick, Schmersal, Omron. Avoid obscure components where you'll need to manually source and verify reliability data. The data from reputable manufacturers is peer-reviewed and accepted without question. Chasing marginal cost savings on safety components is never worth the validation burden it creates.
Validate every safety function separately
Each safety function in your cell needs its own SISTEMA validation — the E-stop circuit, the guard door interlock, the enabling device for teach mode. They are separate functions with potentially different PLr values and different circuit architectures. A single SISTEMA project can contain multiple safety functions, each validated independently.
The SISTEMA report
Once validated, SISTEMA produces a report that shows each safety function, the components entered, the calculated PL achieved, and whether it meets the required PLr. This report goes into your Technical File and forms part of your CE / UKCA marking documentation. Keep it. If the machine is ever modified, the relevant safety functions need to be re-validated and the report updated.
SISTEMA libraries — where to find them
The IFA maintains a list of manufacturer SISTEMA libraries on their website. Most major safety component manufacturers provide these free of charge. When specifying components for your safety circuits, always confirm a SISTEMA library is available before finalising your selection — it will save significant time during validation.
Pilz, Sick, Schmersal, ABB and Rockwell Automation all provide comprehensive SISTEMA libraries covering their safety relay, safety scanner, interlock switch and contactor ranges.
Browse SISTEMA libraries on the IFA websiteWhat happens after SISTEMA
A validated SISTEMA project confirms that your safety circuit design achieves the required Performance Level on paper. The next step is physically wiring those circuits, then testing them during your Factory Acceptance Test to confirm the physical implementation matches the design. That's covered in Part 8 — Testing & FAT.
The SISTEMA report, alongside your ISO 12100 risk assessment and your safety circuit design documentation, forms the core of your Technical File for CE / UKCA marking. None of these documents are optional — they are the evidence that your machine is safe.
Want a pre-built SISTEMA project for a robot cell?
A pre-built SISTEMA project file for a standard industrial robot cell — E-stop circuit, guard door interlock and enabling device, validated to PLd using Pilz components — is coming soon.
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