Introduction to Industrial Automation

4.3.3   Step-by-Step Transition due to a Discrete Successive Signal

Attempting to code the states of a state diagram according to the rule that “from one state to 

another state, no simultaneous variation of two auxiliary variables must exist”, usually we prefer 

an indirect transition of a state to another instead of a direct one. As shown in Figure 4.13, the 

instant signal “x” causes the transition of a system from state S

0

 to state S

2

, through the state S

1

, 

which is understood to a human observer as a one-step transition. In fact, the system first passes 

through state S

1

 and then into state S

2

, due to an instant signal (an example would be the single 

actuation of a pushbutton). In such a case, the state S

0

 has the code “00”, while the state S

2

 can 

have the code “11”, which is impossible if a direct transition from S

0

 to S

2

 has been designed due 

to the same signal.

On the other hand, there are applications where it is desirable for the same pushbutton to 

cause different actions through its successive activations. For example, maybe it is desirable that 

the first activation of a button causes the low speed rotation of a machine, the second activation of 

the same button causes a medium speed rotation, the third activation of the same button a high 

speed rotation, and so on. If we follow the Section 4.3.2 approach of state diagram design, the 

N

A

A

R

b

2

 

b

0

C

1

Β

Α

B

Β

b

1

b

0

A

B

A

 

b

3

 

A

Low speed

C

2

Β

Α

Medium speed

C

3

Β

Α

High speed