Functional Safety in Measurement Technology: SIL and PL Compliant Sensor Solutions from Octogon

In modern industrial plants and machinery, the protection of people, machinery, and the environment is paramount. The Machinery Directive requires reliable proof of the overall system's fail-safety for safety-critical applications. Sensors such as load pins, load cells, and torque transducers are often the first and most crucial link in the safety chain.

Octogon develops and manufactures measurement technology components specifically designed for use in systems with high functional safety requirements according to EN IEC 61508 (SIL) and EN ISO 13849-1 (PL).

Safety Standards: An Overview of SIL and PL

Depending on the industry and the risk assessment of a plant, different standards apply, all pursuing the same goal: reducing the risk of a dangerous machine failure to an acceptable minimum.

SIL (Safety Integrity Level): Defined according to EN IEC 61508. Relevant for the process industry and complex electronic systems. Divided into levels SIL 1 to SIL 4.
PL (Performance Level): Defined according to EN ISO 13849-1. The standard in classic mechanical and plant engineering. Divided into levels PL a to PL e.

For demanding applications in lifting technology or stage technology, specifications such as SIL 3 or PL e are now industry standards. To meet these system requirements, the sensors used must exhibit appropriate architectures and reliability metrics.

Technical Implementation: Redundancy and CCF Avoidance

A single, single-channel sensor cannot inherently meet the highest safety levels. For safety-related applications, Octogon therefore relies on consistent two-channel design (1oo2 architecture) and comprehensive measures to avoid Common Cause Failures (CCF).

Our safety architecture for load pins and sensors includes:

1. True Mechanical and Electrical Redundancy

The sensor's deformation body is equipped with two completely independent strain gauge bridges (SGS). Both measuring circuits detect the same physical force but operate galvanically isolated from each other. If one measuring circuit fails or provides implausible values, the overriding safety system immediately detects the discrepancy and initiates a safe state.

2. Separate Signal Paths and Connections

To prevent crosstalk effects and common cause failures (e.g., a single cable break that severs both signals), internal wiring is physically separated. Connection is made via separate cable outlets or isolated multi-connectors.

3. Diagnostic Capability and Signal Diversity

The safety of a control system depends on its ability to detect sensor faults (Diagnostic Coverage / DC). We support this with various signal configurations:

Inverted Analog Signals: For example, channel A delivers $4 \dots 20\text{ mA}$ , while channel B outputs the inverse $20 \dots 4\text{ mA}$ . A simple addition of the values in the control system must always result in $24\text{ mA}$ – deviations immediately indicate a fault.
Digital Safety Protocols: Fully integrated electronics with protocols such as CANopen Safety or PROFIsafe, which cyclically monitor runtimes, data integrity (CRC), and telegram losses.

Documentation is Part of the Product

A redundant sensor is useless without the appropriate statistical evidence for plant certification. Functional safety requires comprehensive documentation.

Octogon supports machine builders and system integrators not only with hardware but also provides the essential data for Sistema calculations (or comparable tools):

Key Figure	Significance for Plant Certification
$\text{MTTF}_d$	Mean Time To dangerous Failure – The average time until a dangerous failure of the sensor system.
B10d	(For electromechanical components) – Number of switching cycles until 10% of components experience dangerous failure.
DC	Diagnostic Coverage – The diagnostic coverage of our integrated electronic components.
FMEA	Failure Mode and Effects Analysis for identifying and evaluating potential design weaknesses.

Typical Applications

SIL and PL compliant sensors from Octogon are used wherever mechanical failure could endanger human lives or cause immense material damage:

Lifting Technology and Crane Construction: Overload protection and load moment limitation (LML) for mobile, tower, and overhead cranes.
Stage Technology: Wire rope force monitoring above audience and performer areas (rigging).
Automated Guided Vehicles (AGV) & Robotics: Safe force and moment monitoring in human-robot collaboration.
Presses and Forming Technology: Safeguarding closing forces in heavy machinery manufacturing.

Safe machines start with safe sensors.

Are you planning a system according to EN ISO 13849 or EN IEC 61508? Contact the experts at Octogon. We will support you from risk analysis to sensor design and the provision of certification-relevant reliability data.