SIS Testing: Strengths and Limitations of Full Loop Tests and Partial Tests

摘要

Safety Instrumented Systems (SIS) need to be tested to ensure that they can properly respond to a demand when called upon. International standards for SIS design and regulations also require that these systems be tested and place requirements on how the testing is accomplished. One area of controversy is the testing of individual components of a Safety Instrumented Function (SIF) separately, instead of testing the complete loop. The standards allow for partial testing, and in some cases regulations require partial testing of individual components. Many practitioners of SIS design believe that complete loop tests (from sensor to final element) are the only acceptable methodology for testing. The paper will discuss the strengths and limitation of both the partial test and complete loop test approaches to SIS testing, starting with a review of standards requirements, moving on to additional regulatory requirements that are placed on some process industries, and summarizing with best practices and recommendations on performing tests in different process industry applications.