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The influence of systematic failures to the functional safety of automated control systems of hazardous technological processes is considered. It is shown that stability ensuring of the process control system to systematic failures is an actual task for today. Approaches to increase the robustness to systematic failures recommended by IEC 61508 are presented. Special attention is paid to methods based on diversion. The functional diversity and technology diversity have been revealed in detail. Examples of using diversification in railway automation systems are given. The main problems of using diversification to increase resistance to systematic failures are formulated. The main advantages of using diversification are increased resistance to systematic failures and reduced risk of dangerous failures through the usage of diversified protection methods at the functional levels of the APCS. The disadvantages of using diversification are a significant increase in the costs of developing and automated process control system maintenance, the difficulty of confirming the different behavior of diversified channels in case of systematic failures, and the lack of an effective method to assessing the sufficiency of the obtained diversification for a given level of safety integrity.