A Method for Implementing a Safety Control System Based on Its Separation into Safety-Related and Non-Safety-Related Parts

Abstract

International safety standards recommend that control systems should be separated into safety-related and non-safety-related parts. The control circuit is required to have such an interlock function that the control output of the safety-related part gives permission to the control output of the non-safety-related part. This paper describes the methods of separating and combining the safety-related and non-safety related parts in Chapter 2. In Chapter 3, a configuration example of the control circuit for producing a control output is presented. The control circuit is constructed by two fail-safe techniques, or dynamic fail-safe signal processing and voltage-above-supply-voltage processing. The proposed control circuit has such a fail-safe characteristic that it produces no output when the frequent check of its functioning detects a failure in any of its elements. An interlock device constructed by using the two fail-safe processing techniques and containing high-output semiconductor switching elements is shown.