ISO/TC 199/WG 8 - Safe Control Systems

This document specifies a methodology and provides related requirements, recommendations and guidance for the design and integration of safety‐related parts of control systems (SRP/CS) that perform safety functions, including the design of software. This document applies to SRP/CS for high demand and continuous modes of operation including their subsystems, regardless of the type of technology and energy (e.g. electrical, hydraulic, pneumatic, and mechanical). This document does not apply to low demand mode of operation. NOTE 1 See 3.1.44 and the IEC 61508 series for low demand mode of operation. This document does not specify the safety functions or required performance levels (PLr) that are to be used in particular applications. NOTE 2 This document specifies a methodology for SRP/CS design without considering if certain machinery (e.g. mobile machinery) has specific requirements. These specific requirements can be considered in a Type‑C standard. This document does not give specific requirements for the design of products/components that are parts of SRP/CS. Specific requirements for the design of some components of SRP/CS are covered by applicable ISO and IEC standards. This document does not provide specific measures for security aspects (e.g. physical, IT-security, cyber security). NOTE 3 Security issues can have an effect on safety functions. See ISO/TR 22100-4 and IEC/TR 63074 for further information.

This document specifies the safety requirements of a two-hand control device (THCD) and the dependency of the output signal from the actuation by hand of the control actuating devices. This document describes the main characteristics of THCDs for the achievement of safety and sets out combinations of functional characteristics for three types. It does not apply to devices intended to be used as enabling devices, as hold-to-run devices or as special control devices. This document does not specify with which machines THCDs shall be used. It also does not specify which types of two-hand-control device shall be used for a specific application. Moreover, while guidance is given, it does not specify the required distance between the THCD and the danger zone (see 8.8). This document provides requirements for design and guidance on the selection (based on a risk assessment) of THCDs including the prevention of defeat, the avoidance of faults and verification of compliance. NOTE 1 A THCD only offers protection for the person using it. NOTE 2 For specific machines, the suitability of a two-hand control as a suitable protective device can be defined in a type-C standard. If such a standard does not exist or is not appropriate, the risk assessment and determination of suitable protective measures is the responsibility of the manufacturer of the machine. This document applies to all THCDs, independent of the energy used, including: — THCDs which are fully assembled for installation; — THCDs which are assembled by the machine manufacturer or integrator. This document is not applicable to THCDs manufactured before the date of its publication.