scope:

This part of IEC 61800, which is a product standard, specifies requirements and makes recommendations for the design and development, integration and validation of safety-related encoder (Encoder(SR)) in terms of their functional safety considerations, electrical safety and environmental conditions. It applies to Encoder(SR), being sensors as part of a PDS(SR).

NOTE 1 The term "integration" refers to the Encoder(SR) itself, not to its incorporation into the safety-related application.

This document can also be referred to and used for Encoder(SR) in any other safety-related application, for example safety-related position monitoring.

NOTE 2 This document specifies only complementary functional safety, electrical safety and environmental condition requirements that are not clearly provided by other parts of the IEC 61800 series.

This document is applicable where functional safety of an encoder is claimed and the Encoder(SR) is operating mainly in the high demand or continuous mode.

NOTE 3 While low demand mode operation is possible for an Encoder(SR), this document concentrates on high demand and continuous mode. Safety sub-functions implemented for high demand or continuous mode can also be used in low demand mode. Requirements for low demand mode are given in IEC 61508 (all parts) [2]. Some guidance for the estimation of average probability of dangerous failure on demand (PFD_avg) value is provided in IEC 61800-5-2:2016, Annex F.

The requirements of IEC 61800-5-2:2016 for PDS(SR) apply to Encoder(SR) as applicable. This document includes additional or different requirements for Encoder(SR). It sets out safety related considerations of Encoder(SR) in terms of the framework of IEC 61508 (all parts), and introduces requirements for Encoder(SR) as subsystems of a safety-related system. It is intended to facilitate the realisation of the electrical/electronic/programmable electronic (E/E/PE) and mechanical parts of an Encoder(SR) in relation to the safety performance of safety sub-function(s) of an Encoder(SR).

Manufacturers and suppliers of Encoder(SR) will, by using the normative requirements of this document, indicate to users (system integrator, original equipment manufacturer) the safety performance of the Encoder(SR). This will facilitate the incorporation of Encoder(SR) into safety-related control systems using the principles of IEC 61508 (all parts), and possibly its specific sector implementations (for example IEC 61511 (all parts) [3], IEC 61513 [4], IEC 62061 [5] or ISO 13849-1 and ISO 13849-2 (see Clause 2).

By applying the requirements from this document, the corresponding requirements of IEC 61508 (all parts) that are necessary for an Encoder(SR) are fulfilled.

This document does not specify requirements for:

• the functional properties of an Encoder(SR) without any safety relevance;

• the hazard and risk analysis of a particular application;

• the identification of safety sub-functions for that application;

• the initial allocation of SILs to those safety sub-functions;

• the driven equipment except for interface arrangements;

• secondary hazards (for example from failure in a production or manufacturing process);

• the Encoder(SR) manufacturing process;

• the validity of signals and commands to the Encoder(SR); and

• security aspects (e.g. cyber security or Encoder(SR) security of access).

NOTE 4 The functional safety requirements of an Encoder(SR) are dependent on the application, and can be considered as a part of the overall risk assessment of the installation. Where the supplier of the Encoder(SR) is not responsible for the driven equipment, the installation designer is responsible for the risk assessment, and for specifying the functional and safety integrity requirements of the Encoder(SR).

This document applies to Encoder(SR) implementing safety sub-functions with a SIL not greater than SIL 3.

This document provides additional information for Encoder(SR) claiming conformity with ISO 13849-1:2015.

Figure 1 shows the installation and the functional parts of a PDS(SR) including the Encoder(SR) (sensor) which is considered in this document.

Figure 1 shows a logical representation of a PDS(SR) rather than its physical description.