Introduction to Industrial Automation

Figure 4.14  State diagram with double transition due to an instant signal b.

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  Introduction to Industrial Automation

It is clear by inspection of this circuit logic that by pressing once the button b, both relays A and 

B are energized (the first relay B is actuated and then immediately relay A is also actuated) leading 

to the simultaneous start of the operation of both machines M and N. Therefore, the question is 

“How can we succeed the desired step-by-step activation of different machines through the discrete 

successive signal coming from the same device?” Such a device may be a sensor, a pushbutton, a 

switch contact, etc. It must be noted that the two power relays M and N are identical to the auxil-

iary relays A and B from the logical point of view and hence the auxiliary relays are not necessary. 

The introduction of the auxiliary variables are in order to follow exactly all the steps of the state 

diagram design method.

The key action for the step-by-step transition to succeed is to introduce the signal 

b

 as condi-

tion for outputting from a state. This means that the operator who presses a button once to activate 

a machine has to release the button b first and then press it again for a second time in order to 

activate another machine. This state diagram designing procedure is applied to Example 4.5, as 

follows.