A method for designing ladder diagrams for sequencing tasks is described. it is systematic, fast, and simple to apply. The method is applicable to both programmable controllers and hard-wired relay circuits. While it ...
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A method for designing ladder diagrams for sequencing tasks is described. it is systematic, fast, and simple to apply. The method is applicable to both programmable controllers and hard-wired relay circuits. While it does not minimize the number of required relays, this should be no problem when working with programmable controllers. The method is based on the idea of dividing the required sequence into groups according to a simple rule. These groups are then encoded using the "one-hot" code, with each group assigned one relay set up to operate as RS-flip-flop. The various operations belonging to a particular group result each in a single ladder-diagram line. The method can also be adapted to systems with multiple-path programs having one or more random inputs. This is of special importance when using simple, low-cost programmable controllers, which usually do not provide conditional jumps. Four examples of such multi-path programs are presented: Two or more simultaneous parallel paths; two or more alternative parallel paths; option of by-passing certain steps; and option of repeating certain steps. The method has been used successfully in an instructional automation laboratory at the author's institute.
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