What is Performance Level (PL)?
Performance Level is a rating used to measure the reliability of safety-related parts of control systems. It’s defined by two key safety standards:
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DIN EN ISO 13849-1 – covers machinery safety
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ISO 25119 – focuses on the functional safety of electronic systems in agricultural and forestry machinery
PL ratings range from PL a (lowest safety level) to PL e (highest). To determine the appropriate level, three main factors are considered:
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Hardware Category (1–4): System architecture and redundancy
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Diagnostic Coverage (DC): The ability to detect failures
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Mean Time to Dangerous Failure (MTTFd): Expected lifespan before a dangerous failure might occur
To meet PL d, a system must have:
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A failsafe architecture capable of detecting faults
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Diagnostic coverage greater than 90%
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An MTTFd typically greater than 100 years for electronic components
What does Performance Level d (PL d) mean for RAFI’s SAFETY TOUCH®?
In industries like agriculture, construction, and heavy machinery, safety is non-negotiable. Human-machine interfaces (HMIs) play a critical role in how operators interact with equipment, and these systems must be built with safety in mind.
SAFETY TOUCH® is engineered to meet the rigorous demands of functional safety by achieving Performance Level d (PL d) compliance. However, SAFETY TOUCH® is a touchscreen, which inherently comes with obstacles to overcome.
Why is achieving PL d with a touchscreen so complex?
Unlike traditional safety components, like E-stop buttons or dual-redundant sensors, touchscreens come with their own unique challenges when safety is on the line. Here’s how RAFI addresses them:
1. Reliable Touch Detection
Standard capacitive touchscreens aren’t inherently safe. They typically lack redundancy and can’t distinguish between intentional and accidental touches.
SAFETY TOUCH® changes that by combining multiple sensing mechanisms with force detection. This setup confirms that a touch is deliberate before registering it, helping avoid unintended activations.
2. Display Integrity and Verification
A screen that shows the wrong information, or fails to display at all, can mislead operators and lead to unsafe conditions.
SAFETY TOUCH® includes both optical and electrical monitoring to detect display issues in real time. It also performs content integrity checks to ensure the right information is always visible to the user.
3. Fault Detection and Diagnostics
Because full hardware redundancy is often impractical in touchscreens, SAFETY TOUCH® relies on smart diagnostics to ensure safety.
Through Failure Modes, Effects, and Diagnostic Analysis (FMEDA), potential system faults are identified and addressed. This enables the system to meet the >90% diagnostic coverage requirement of PL d.
Key features include:
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Real-time error detection and alerts
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Smart algorithms that differentiate between real and false inputs
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Ongoing self-tests of the LCD, touch sensor, controller, and communications interface
4. Durability and Long-Term Reliability
To meet PL d, the system’s components must be designed to last, often more than 100 years in theoretical usage terms.
Touchscreens used in heavy machinery face constant vibration, harsh environments, and temperature swings. SAFETY TOUCH® uses industrial-grade components that have passed rigorous lifetime testing to ensure long-term reliability in the field.
Ensuring functional safety in touch-based HMIs is no small task, but it’s one we take seriously. With its layered sensing, robust diagnostics, and durable components, SAFETY TOUCH® meets the demanding requirements of Performance Level d.
And because it allows safety-critical inputs to happen directly on the screen, it gives design teams more flexibility, less reliance on hard-wired buttons, more freedom in layout, and better ergonomics for the operator.
SAFETY TOUCH® isn’t just a touchscreen, it’s a smarter, safer way to interact with your machine.