A safety related analog input module based on diagnosis and redundancy

This paper introduces a safety-related analog input module to achieve data acquisition of 4-20mA current signals. It is an integral part of the safety-instrumented systems (SIS) which is used to provide critical control and safety applications for automation users. In order to ensure the performance of analog input circuit in good condition, a combination of hardware and software diagnosis should be carried out periodically. These kinds of internal self-diagnosis allow the device to detect improper operation within itself. If potentially dangerous process occurs, the AI has redundancy to maintain operation even when parts fail. The article presents special hardware, diagnostic software and full fault injection testing of the complete design. The test result shows that the safety-related AI is capable of detecting and locating of mostly potential faults and internal component failures.