Introduction to Industrial Automation

Figure 7.53  (a) Counting luggage on a belt conveyor set-up (b) PLC wiring of the related auto-

mation components.

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  Introduction to Industrial Automation

The indirect presetting of a counter to a value through a data file is used when the controlled pro-

cess can work with two or more scenarios. Of course, in the luggage conveyor example, something 

similar it is not obvious, but let’s consider the following case. If a loading transport vehicle of type A 

is used, then counting 100 pieces of luggage should be performed when a loading vehicle of type B is 

used, so the maximum count should be 200. Changing the value of this parameter cannot be done 

in the program each time it is required, because it will be a time-consuming process (programming 

device, program opening, value correction, downloading program, etc.). Instead, this change should 

be performed simply by a corresponding selector switch. The automation program, depending on the 

position of the switch, will then perform the change in the numeric value of the parameter. These 

two, or in the general case of more alternative values of a parameter, are usually stored in a data block 

from where the main automation program calls them. For this example, obtaining only the value of 

200 from a data block by pressing the set button is implemented with the following program:

DB16

OPN  D B15

A

I0.5

CD

C10

A

I0.0

L

DBW2

S

C10

A

I0.3

R

C10

AN C10

=

Q2.3

BE

DB15

0:

0

1:

100

2:

200

3:

300

4:

0

..

.

BE

DB16

DB15

0:

0

1:

100

2:

200

3:

300

4:

0

..

.

word

numb er

BE

Comparison of numerical values. Figure 7.54a shows a conveyor belt transferring caps of switches 

from the production department to the final packaging section. Photocell 1 (PC

1

) counts all the 

caps passing in front of it, whereas photocell 2 (PC

2

) detects if there is a cap of different size. When 

 

 

 

 

(b)

(c)

(a)

PLC

Inputs

Outputs

0 V

+24 V DC

0 V

+24 V DC

I0.0

I0.3

I0.5

Q2.0

Set

 

PC

1

Reset

 

PC

2

I0.7

h

1

h

2

h

3

h

4

Q2.2

Q2.4

Q2.6

PC

1

PC

2

PC

1

PC

2