Introduction to Industrial Automation

7.5.4   Using Structural Programming

The purpose and benefits of structural programming were discussed in Section 7.3, where the 

basic structural components of such an automation program have also been described (e.g., the 

three types of POUs). Here, how to implement structural programming with specific examples 

is presented. Figure 7.56 shows the I/O connections in the PLC for three direct-starting motors 

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  Introduction to Industrial Automation

PLC

Inputs

Outputs

0 V

(a)

(b)

+24 V DC 

0 V

+24 V DC 

I0.0

Q2.0

I0.3

Q2.3

Q2.6

STOP

START

C

1

C

2

C

3

T3

0

Remaining time 18 sec

1st machine starts immediately

2nd machine starts after 5 sec

Remaining time 13 sec

3rd machine starts after 10 sec

Remaining time 8 sec

4th machine starts after 15 sec

Remaining

time 3 sec 

0

(T3, time setting)=18 sec

Figure 7.55  Start of machines with time difference between each other, (a) PLC electrical wir-