Introduction to Industrial Automation

Figure 4.15  Automation circuit confirming the double transition of the state diagram, which 

means the auxiliary relays A and B are energized both with only one press of the button b.

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Logical Design of Automation Circuits 

◾

 

131

The introduction of three auxiliary variables is necessary for the six states of the system. For the 

code assignment shown in Figure 4.16, we obtain the following equations:

 

Turn ON of A b

Turn OFF of A b

Turn ON of B

=

=

=

BC

BC

,

bbA

Turn OFF of B

Turn ON of C b

Turn OF

C

s AC

AB

,

,

=

=

1

FF of C

=

s AB

2

Applying the formula (1) to the three auxiliary variables, we obtain,

 

A

b B C bBC A

= + +

+

(

)(

)

 

B

s A C bAC B

=

+ +

+

(

)(

)

1

 

C

s

A B bAB C

=

+ +

+

(

)(

)

2

For the operation of the two machines we have,

 

M ABC ABC ABC ABC AC AB

=

+

+

+

=

+

 

N ABC ABC ABC AB ABC

=

+

+

=

+

Converting the above equations to an automation circuit, we obtain the circuit shown in Figure 4.17.

S

5

S

0

s

2

S

1

b

s

1

Μ=0

Ν=0

Μ=1

Ν=0

Μ=1

Ν=1

S

4

ABC

000

Μ=0

Ν=1

100

S

3

S

2

b

Μ=1

Ν=0

b

b

Μ=1

Ν=1

110

010

011

001

Figure 4.16  State diagram including the complement of a signal (

b

) as a condition for separat-

ing successive actuations.

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132

 

◾

  Introduction to Industrial Automation

Example 4.7:  Power Factor Correction by Manual Insertion of Capacitors

The manual correction of the power factor (cos

φ

) in an industrial electric AC power station is 

performed by inserting successively capacitors to the power circuit until it reaches the desired 

factor value. The insertion of capacitors is achieved by energizing an equal number of relays and 

by pressing the same button several times. In a similar way, the technician who monitors and cor-

rects the power factor can subtract capacitors by pressing another button. The number of inserting 

capacitors may be greater than 10 or 12 stages, but in this example, we will examine the case of 

four capacitors and only the insertion mode due to space limitations. The required state diagram is 

shown in Figure 4.18, containing ten states and four auxiliary variables. Also, it is obvious its form 

is extendable and hence this can be a guide for the case of larger number of capacitors. It should 

be noted that the transitions from state S

8

 to S

0

 are included for the tutorial scope only in order 

to have a closed diagram and hence a repeatable procedure. In other words, it is not technically 

accepted to subtract all the capacitors in one step. In a real system, these transitions are missed 

and the return of the system from state S

8

 to state S

0

 will be performed via the above-mentioned 

subtraction pushbutton.

N

A

R

M

Α

Α

C

Β

A

B

Α

A

C

s

1

C

B

C

A

B

C

N

C

Β

b

b

 

Β

C

b

 

s

2

B

A

C

b

 

Α

Β

Α

Β

Figure 4.17  The automation circuit of the two machine Example 4.6 extracted from the state