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Abstract

Programmable logic controllers are microprocessor-based solid state switches that can be programmed to operate in a particular sequence in response to such external inputs as pressure or temperature indication. These units are now being installed to control primary and peripheral processes, including the burner management/safety environment, in place of the more traditional electromechanical controls. Specific design guidelines that will successfully manage the several identified failure modes of programmable logic controllers are discussed. Suggestions as to how this philosophy may be applied to actual installations are provided.