Safety Controls SIL and PL

The controls for a machine usually include one or more safety features. A safety control consists of a number of safety components, all of which function together. Examples of safety features include two-hands operation, glare shield, circuit pad, hold-to-run operation, function blocking with or without a lock, etc. Your choice of safety components for the controls circuit and their reliability should be based on a risk assessment.

Standards following on from EN 954-1

The most important standard for the design principles for safety controls was EN 954-1, which was revoked on 31 December 2011. EN 954-1 was developed on the basis of the available technology a number of years ago, when all safety features were still hardware-operated. Nowadays technology is much more advanced due to the invention of safety software, bus systems, complex electronics and safety PLCs and PSs. There are already PLCs in existence containing the entire integrated functional and safety controls. The standards that have replaced EN 954-1 are EN-ISO 13849-1 (PL = Performance Level) and EN-IEC 62061 (SIL = Safety Integrity Level). Both these standards have already been harmonised under the Machinery Directive and are widely applied. Although the old standard (EN 954-1) was based on a qualitative risk assessment only, the new SIL and PL standards also require calculations to be made showing that the design complies with these standards with respect to all parts of the safety controls.

Performance Level (PL)

The aim of EN-ISO 13849-1 is to provide machinery manufacturers with a tool for simple safety controls in order to classify a target performance level and verify it. This standard is suitable for relatively simple electromechanical, pneumatic and hydraulic safety circuits.

Sistema calculation tool

The free Sistema software tool on the IFA website can be used to carry out classification and verification in a simple manner. All D&F’s training courses on PL devote considerable attention to working with Sistema, as well as practical tips on how you can use this tool yourself in everyday practice. Sistema contains a large number of libraries from various component suppliers which include data on the chances of failure.

Safety Integrity Level (SIL)

SIL classification, verification and validation is widely accepted in the chemicals industry as a standard for component and system reliability. The main standard, IEC 61508, is a comprehensive standard on which the SIL standard for machine construction (EN-IEC 62061) is based. Although the calculation methods are different, they are not more complex in principle. IEC 62061 specifies the calculation methods for classifying, verifying and validating the target SIL, and is ideal for electronic and programmable safety circuits.

The IEC 62061 standard refers to ISO 13849 for the calculation of electromechanical, pneumatic and hydraulic safety circuits. Table 1, which is given together with the applicability in both standards, is out of date and has been superseded.

Both standards must be applied for combined safety circuits with e.g. hydraulic and programmable safety circuits. You should use ISO 13849 to calculate the parameters for the hydraulic components. You then use the results in the IEC 62061 calculations for the programmable safety controls, i.e. as a whole with the hydraulic parts included.

D&F: your expert on SIL and PL 

Advice and coaching on SIL and PL

We offer you specific tailor-made solutions for your company, such as carrying out risk assessments for machinery, assembling machinery, systems and processes, determining the safety features for designing safety controls, e.g. two-hands operation, hold-to-run, glare shields, mode selectors, function blocking with a lock, stopping times, etc. and compiling the safety requirements specification for classifying the SIL target and PL required.

Training courses on SIL and PL

D&F gives extremely practice-oriented training courses on electrical systems for machines and safety controls, SIL and PL, including practical tips on working with Sistema yourself. These training courses vary from one-day courses to a complete 4-day master class.

Click here for a full overview of D&F’s training courses on SIL and PL.

Useful SIL and PL trilogies (free of charge)

D&F’s aim is to lead the market in our own fields of expertise. Our KneX! teams (knowledge teams) make useful pocket-sized trilogies. You can ask us to send you these free of charge after you’ve registered. 

  • Click here to order the “Safety Integrity Level for Machine Construction” trilogy.
  • Click here to order the “Performance Level for Machine Construction” trilogy.
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