1756-RM001B-EN-P, Using ControlLogix in SIL2 ... - Tuv-fs.com

Chapter 10Use and Application of Human toMachine InterfacesNo specific device is part of the certification because the variety ofdevices is so large, ranging from simple thumb-wheel and LEDreadouts to PC/CRT-based human to machine interface (HMI) deviceson a variety of networks. The range and breadth of these devices issimilar to that of sensors and actuators; it would be impractical toimpose device restrictions.Using Precautions andTechniques with HMIHowever, users must exercise the same precautions and techniqueson HMI devices as on simple devices such as sensor and switchinputs. The precautions include, but are not restricted to:• Limited access and security• Specifications, testing and validation• Restrictions on data and access• Limits on data and parametersFor more information on how HMI devices fits into a typical SIL loop,see Figure 1.2 on page 1-4.Sound techniques should be used in either the application softwarewithin the HMI or PLC in safety-related systems and non-safety-relatedsystems.Accessing Safety-Related SystemsNormally, when accessing the safety-related system, the HMI shouldbe restricted to read data and information such as diagnostics. Theuser should use techniques to limit access to only those sections ofmemory that are appropriate. For more information, see Figure 1.2 onpage 1-4.If parameters in safety-related system require a change from an HMI,users should follow the guidelines indicated in the next section.1 Publication 1756-RM001B-EN-P - October 2003