Introduction to Industrial Automation

Figure 4.29  The system state diagram for Example 4.10.

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  Introduction to Industrial Automation

Second, the minimum realization of the circuit is the one generated from the empirical approach, 

which is something that might sound awkward. However, we should remember that in these state 

diagram approaches, state reduction techniques have not been applied and thus, such a result when 

examining minimum realizations might happen. In many real cases it is possible to have an indus-

trial automation circuit with more switching contacts or a few more auxiliary relays than another 

one implementing the exact same logic. This happens mainly due to neglect of the state reduction 

approaches during the design phase, and it is not a serious cost problem, since the automation cir-

cuit, in most cases, will only be implemented once for a specific and unique application. This is in 

contrast to the logical design of integrated circuits (ICs), where the extended application of state 

reduction techniques is fundamental, mainly due to their production number, which can be equal 

even to thousands or millions of replications of the same circuit, and thus, in this case, the corre-

sponding cost demands minimum realizations.

Third, the characteristics of the automation circuits shown in Figures 4.28 and 4.30 are worth 

mentioning. The circuit in Figure 4.28 has two buttons of dual contacts, in contrast with those 

shown in Figure 4.30 that have single contacts. The timer T in Figure 4.29 has only one delayed 

contact, while the corresponding one in Figure 4.30 has two delayed contacts. Since timers usually 

have only one delayed contact or output, the implementation problem can be easily overcome by an 

additional auxiliary relay.