Design of a fault-tolerant voter for safety related analog inputs
This paper introduces a voting scheme for safety-related analog input module to arbitrate between the results of redundant channels in fault-tolerant system. The design approach is a distributed system using a sophisticated form of duplication. For each running process, there is a backup process running on a different CPU. The voter is responsible for checkpointing its state to duplex CPUs. In order to increase the dependability for safety-related controllers, the I/O modules use redundancy to reduce the risk associated with relying upon any single component operating flawlessly. The 1oo2D voting principle is commonly used in fault tolerant I/O modules to provide passive redundancy for masking runtime faults at hardware and software levels, respectively. A dual architecture (1oo2D) which provides high safety integrity to a rating of SIL 3 is presented. The outputs from two identical channels operating in parallel with the same inputs are supplied to a voting unit that arbitrates between them to produce an overall output. Based on the hardware logic model and FPGA technique, the study adopts the hardware voter which has much more advantage in the velocity and reliability. Finally, using modelsim simulations, we verify the effectiveness of the proposed voter design in preserving the hazard-free property of the response of an analog inputs module.