Introduction to Industrial Automation

Figure 7.51  Implementation of the conventional OFF-delay stopping circuit in a PLC. 

(a) Conventional circuit, (b) implementation with PLC and (c) program.

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  Introduction to Industrial Automation

in Figure 7.52c, the required Boolean language program, for T

1

 = 20 s and T

2

 = 80 s is the 

following:

AN T2

L

‘20 sec’

SD   T1

A

T1

L

‘80 sec’

SD T2

A

T1

=

M3.4

A

I1.1

A

M3.4

=

Q0.2

BE

Counters. Counting as is a very common function in all industrial environments. There is no 

industrial production process (especially consumer products from beer or water bottles, to medi-

cines boxes, to all kinds of food packaging) that does not require enumeration of objects. A series 

of features associated with the operation of a counter is the ability to place it at an initial value, to 

increase or decrease its content, to define the step of its content change and to reset its current value. 

Figure 7.53a shows a conveyor belt for carrying luggage that is counted by the photocell (PC). The 

input devices that affect the counting function of the PLC are shown in Figure 7.53b. With the set 

button, the counter is set at an initial value of 100. With the reset button the contents of the counter 

are reset for any reason and at any time. It is desired when 100 pieces of luggage are counted that 

the relay C

1

 is activated. The required Boolean language program is as follows:

A

I0.5

CD C10

A

I0.0

L

‘100’

S

C10

A

I0.3

R

C10

AN C10

=

Q2.3

BE

A

I0.5

CD C10

A

I0.0

L

‘100’

S

C10

A

I0.3

R

C10

AN C10

=

Q2.3

BE

PLC

Inputs

Outputs

S1

Sensor

0 V

C

+24 V DC 

0 V

+24 V DC

Q 0.2

I 1.1

N

d

S

1

R

(a)

(b)

(c)

T

1

T

2

T

2

T

1

C

T

1

d

d

T

1

T

2

T

1

T

2

t

T

1