8 - Programmable systems for safety controls

Abstract

This chapter focuses on several programmable logic controller (PLC) systems for safety controls. SafetyBUS-p allows up to 32 subsystems to be linked and interfaced to a safety PLC. Local safety interlock functions are performed in the subsystems using safety-certified program blocks. Peer-to-peer communications permit safety functions to operate without a host. The actuator–sensor bus system allows single-cable networking of safety and nonsafety devices with data transfer to plant-level controls. Safety monitors are parameterized to carry out safety functions and act as hosts for a cluster of devices. In this design, fail-safe and basic control system components share the same network. Some of the features of this plant-wide bus design are that safety devices can connect directly to the network with fail-safe communications ports; safety function messages are event-driven and hence have rapid response; and fail-safe I/O subsystems ensure safe shutdown on loss of communications.