Safety architecture

The Functional Safety Revolution in Electrohydraulics

Feb. 9, 2021
The Functional Safety Revolution in Electrohydraulics

Everyone has seen how digital technology has been changing our lives and, with the advent of the Fourth Industrial Revolution, is the central focus in the industrial sector. Digitalization has created the basis for fieldbuses, diagnostics and functional safety, now essential conditions to engineer smarter and safer Industry 4.0 machines.

Functional safety is the ability to detect a potentially dangerous condition and activate a protective mechanism to prevent raising hazardous events. The Machine Directive 2006/42/EC with relevant harmonized standards IEC 61508 Safety Integrity Level (SIL) and ISO 13849 Performance Level (PL) define the general principles concerning machine safety which manufacturers must consider in order to limit risks related to machine operation.

Consequently, hydraulic systems designers need to extend their competence and responsibility in dealing with safety regulations related to the risk prevention for workers and equipment in case of system fault or human error. They are also investing energies and time in components validation and the relative overall system certification process.

Certified safety valves eliminate the need for machine manufacturers to validate such components in compliance with the applicable safety standards. A considerable amount of time is saved during the machine design, resulting in a simplification of the system certification process.

The standard solution foresees the use of on-off valves or cartridges with inductive safety sensors to monitor the spool or poppet position, information which the machine central unit collects in order to confirm the safe status of the valve.

On-board Electronics

The innovation is represented by new digital proportional valves with on-board electronics designed for functional safety and certified by a notified body. They meet safety standards by performing the safety function in addition to axis motion control or standard valve regulation.

The safety function is operated to limit potential risks to equipment or operators by preventing dangerous movements of electrohydraulic axes during machine cycles. It is activated by the machine central unit in case of emergency, which inhibits the regulation of proportional valve via on-off enable signals. The valve confirms when a safe spool position has been reached; this information is managed by the machine central unit as a “safe condition.”

Of course, overall system SIL and PL levels do not depend solely on the characteristics of a single component. Moreover, SIL and PL levels are determined by hydraulic system architecture, diagnostic coverage of that system and the entire chain of safety-related parts used to perform the safety function. Architecture plays a fundamental role: On-off and proportional controls can be integrated in redundant double channel systems to achieve higher safety levels, as well as increasing the complexity of the systems.

In the last year, functional safety in hydraulic systems has become more and more important and is no longer optional; it’s now a basic requirement for every manufacturer. Certified valves support engineers in designing safer systems without wasting time in components validation versus the applicable safety standards.

Fabio Balzarini is technical sales manager for Atos.

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