Jari Rauhamäki

Patterns for control system safety

The main purpose of a control system is to operate a system under control so that it functions as desired. However, when a control system for a plant, process or device is being designed, safety-related aspects also need to be considered. In this article four design patterns for control system safety are illustrated. The patterns consider software architecture to implement interlock mechanism, design of the system to be safe when de-energized, and to check that operation in software has the desired response in the physical world. The patterns are applicable to safety systems and to control systems with safety-related aspects.

Strategies for hazard management process II

When a system is being designed, the hazards and corresponding risks introduced by the system must be identified. Mitigation of risks is required if they are found intolerable. To mitigate risk there are multiple valid possibilities, but some are more preferable than other. Hazard elimination is the most preferable approach but it is not always applicable. In such case substitution, isolation and active protective measures in form of electric, electronic and programmable electronic systems need to be considered. In this paper, we illustrate some hazard management methods and provide the suggested order of consideration for the methods in format of strategy collection.

Patterns for Safety System Bus Architecture

Traditionally safety and controls systems have been strictly separated from each other. There are both benefits and liabilities in this approach. Thus, modern system employing control and safety system parts do not necessarily make a strict separation between these two elements of the system. Regardless of the degree of separation, the nodes belonging to either control or safety system may need to communicate with each other to implement the desired functionality. An increasing number of systems nowadays utilize a fieldbus to connect the distributed nodes of the system together. A time comes in the design process, when one needs to select the architecture of the physical fieldbus. That is, how and which nodes are connected? In this paper, two patterns to organize the fieldbus architecture are illustrated. In short, one either can separate the fieldbus between the safety and control system nodes or use a shared fieldbus between the nodes.

Patterns to implement active protective measures

There are various ways to protect people, environment and other systems from harm caused by machines and system. In this paper, patterns on implementing protective measures applying an active approach are given. The purpose of a protective measure is to lower the risk related to a hazard by either reducing the likelihood (the frequency of exposure of) or the consequences of a realization of harm. The protective measures can, for example, protect user from harms introduced by hazards in the system or operations of the system operator.

Patterns for Sharing Safety System Operation Responsibilities between Humans and Machines

Although the automatic operations of machines, processes, and systems have increased, human operators are still typically required to operate or monitor the system or operate in proximity of the considered process or system. As people operate the systems and in their proximity, they have a role in the overall safety system operation. Automated safety systems, which primarily ensure a safe operation of the system under control, have properties that humans are not capable of, but they are not perfect either. In this paper, two patterns for sharing the responsibilities between automated safety systems and human operators are presented. The strengths of automated safety systems and human operators are combined so that the weaknesses of the other can be overcome.