Introduction to Industrial Automation

NO STOP pushbutton.

---

304

 

◾

  Introduction to Industrial Automation

connected to two different outputs and their parallel operation is achieved by proper program-

ming. The required Boolean program is as follows:

A

I1.0

A

I1.2

A

I1.4

=

Q0.0

AN I1.0

AN I1.2

AN I1.4

=

Q0.2

=

Q0.4

BE

In Figure 7.31a a simple OR logic circuit is considered, including three-sensor switching 

contacts; S

1

, S

2

, and S

3

. In this case, it is desired that the relay C

1

 is activated when either the 

contact S

1

 closes or the contact S

2

 is closed or the contact S

3

 closes. For a similar connection of 

the input devices to the PLC, as presented in Figure 7.31b, the required Boolean program is the 

following:

O

I1.0

O

I1.2

O

I1.4

=

Q0.2

BE

In the next programming example, the OR instruction, without a reference to a variable, will 

be utilized. This instruction has the same logic as the simple OR instruction, except that it does 

not refer to a specific variable, but to a complex logical expression from individual instructions that 

usually have an AND logic. In the circuit of Figure 7.32a, it is desired that the relay C

1

 is activated 

0 V

PLC

INPUTS

OUTPUTS

Q 0.0

I 1.0

I 1.4

Q 0.2

Q 0.4

I 1.2

PLC

INPUTS

OUTPUTS

Q 0.0

I 1.0

I 1.4

Q 0.2

Q 0.4

I 1.2

C

1

+24 V DC

S

1

C

2

S

1

S

2

S3

S

2

S3

C

3

PLC

Inputs

Outputs

0 V

(b)

(a)

C

1

+24 V DC 

0 V

+24 V DC 

Q 0.0

I 1.0

I 1.4

S

1

S

3

C

2

Q 0.2

C

3

Q 0.4

S

2

I 1.2

Figure 7.30  A conventional automation circuit (a) with a series of logic AND in both the