Introduction to Industrial Automation

branches and connection status of I/O devices for implementation in a PLC (b).

---

Basic Programming Principles of PLCs 

◾

 

305

when either the contacts S

1

 and S

3

 are closed and the contact S

2

 remains closed; the contact S

4

 is 

closed; or the contact S

5

 is closed and the contact S

6

 remains closed. For this example, the con-

nection of the input devices is performed as presented in Figure 7.32b, while the required Boolean 

program is as follows:

A I1.0

A I1.2

A I1.4

O

A I2.0

O

A I2.2

A I2.4

= Q0.3

BE

A I1.0

A I1.2

A I1.4

O

A I2.0

O

A I2.2

A I2.4

= Q0.3

BE

After this first programming experience with some instructions expressing the Boolean logic 

and the simple activation instruction, the creation of the RLO in an entire small-sized program will 

be examined, since until now the RLO examination has been limited to individual instructions. 

+24 V DC

PLC

INPUTS

OUTPUTS

I 1.0

I 1.4

Q 0.2

I 1.2

0 V

C

1

(a)

(b)

S

1

S

2

S

3

S

1

S

2

S

3

PLC

Inputs

Outputs

0 V

+24 V DC

0 V

+24 V DC 

I1.0

I1.4

C

1

Q0.2

I1.

2

Figure 7.31  A conventional automation circuit with parallel contacts (a) and connection status