Introduction to Industrial Automation

Figure 4.22  A multi-conveyor system feeds an assembly station.

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Logical Design of Automation Circuits 

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137

 

C

T PS C

C

T PS

C

C

T PS

C

C

T C C C

1

1

1

2

2

2

3

3

3

4

1 2 3

=

+

=

+

=

+

=

(

)

(

)

(

)

(

++

=

+

C

C

T b C

C

4

5

0

4

5

)

(

)

For the operation of the active components we have

 

H

C H

C H

C H

C , C

T C

M

1

1

2

2

3

3

4

4

5

=

=

=

=

= =

,

,

,

.

Converting the above equations to an automation circuit and after some obvious simplifications, we 

obtain the circuit shown in Figure 4.24.

As we ascertain by the inspection of the automation circuit shown in Figure 4.24, the relays C

1

, 

C

2

, and C

3

 may be characterized as auxiliary relays, but have been introduced in the circuit without 

the use of auxiliary variables and binary coding that is a basic easiness of the above modified state 

diagram method applicable to similar problems.

4.3.6   State Diagrams and Minimum Realizations

In most cases, automation problems do not have a unique solution. Different methods of circuit 

design can produce different automation circuits. As many solutions as there are to an automation 

problem, only one of them is the minimum implementation, i.e., the solution with the smallest 

possible number of relay contacts and auxiliary relays. The design of an automation circuit which 

is not the minimum implementation does not constitute a mistake or an implication problem. The 

main and important goal is for the circuit to operate correctly, satisfying the specifications for the 

overall system’s operation. Let’s clarify these non-identical solutions derived from different design 

methods by an example.

C

3

C

4

S

0

C

2

C

5

C

1

b

0

•C

4

PS

2

PS

3

T

PS

1

C

1

•C

2

•C

3

T

T

T

T

Figure 4.23  The component state diagram of the multi-conveyor system feeding an assembly 

station.

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  Introduction to Industrial Automation