Introduction to Industrial Automation

Figure 7.69  Temperature regulation via ON-OFF control performed by the PLC.

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  Introduction to Industrial Automation

more easily despite any other equivalent numerical values. Details of the required analog value 

scaling are given in Appendix B. Therefore, in order for the above program to be correct, it is 

assumed that the MW100 contains the scaled value of the analog input.

Layout for separating objects. Figure 7.70 shows a layout for separating objects differing in 

height. The whole system is turned on via a switch RS, when the conveyors M

0

, M

A

, and M

B

 start 

to operate. At the same time, the contents of the counters and timers that are possibly utilized 

are reset. The photocell PC

2

 detects the objects B that should be led to the conveyor belt B (M

B

). 

To do this, the cylinder C

B

 has to be extended while the cylinder C

A

 is inside. The photocell PC

1

 

detects objects A, but it is also triggered by objects B, which will be handled by the logic program-

ming. The objects A are driven on the conveyor belt A (M

A

) with the cylinders C

A

 and C

B

 to be 

both in retracted status. The combination of the C

A

 and C

B

 cylinders is attached to the movable 

part of the conveyor M

0

, which can occupy one of the three positions: A, B, and C. When 1000 

objects are counted, whether they are A or B, the next objects are guided to position C with the 

C

A

 and C

B

 cylinder pistons both in extraction status, while both the conveyor belts M

A

 and M

B

 

stop. This continues until a reset in the operation of the layout is performed by the switch RS, 

whereby the conveyor belt M

0

 also stops. Furthermore, it is desired that, if for any reason, it does 

not reach an object A or B (in front of photocells) for a time interval of 10 min, a light indicator 

A

B

A

B

C

PC

1

PC

2

C

C

C

Β

M

0

M

Α

M

Β

PLC

Inputs

Outputs

0 V

+24 V DC

0 V

+24 V DC

Q2.0

I0.1

Q2.2

Q2.4

Μ

0

Μ

Α

Μ

Β

I0.3

I0.4

C

Β

C

C

h

PC

2

PC

1

RS

Q3.0

Q3.2

Q3.4