Increase in Trustworthiness of Checking the Digital Components in Safety-Related Systems

The possibilities of increase in trustworthiness of on-line testing methods in checking of the results calculated in digital components of instrumentation and control safety-related systems which are widely used in power engineering including cryogenic applications are considered. Approach to increase in trustworthiness of checking the results on the basis of distinguishing of the essential and inessential errors caused in approximate result by failure of digital circuits with raised functional checkability is offered. For operations of multiplication and division of mantissas, the result models which are its upper and lower boundaries are proposed. These models are based on the restrictions determined for the normalized numbers by the modern floating-point formats. Models are evaluated on their root mean square deviation from results. On a set of models of result, the methods checking the mantissas by inequalities are defined. They provide distinguishing of essential and inessential errors. The methods are oriented on circuits of the iterative array multipliers and dividers executing the truncated operations with mantissas. Such circuits are characterized by the raised dualmode functional checkability which is provided due to abbreviation of array structures. Methods are evaluated on probability of error detection and trustworthiness in checking of results. Errors are detected depending on their value more likely in most significant bits in comparison with least significant bits. It provides the high trustworthiness in checking of mantissas important for safety-related systems.