Introduction to Industrial Automation

3.8.1   Machine Operation Control from Multiple Positions

Let’s consider the problem of controlling a machine from multiple different locations, which 

means that it is required to have the ability to start or stop the machine from every control posi-

tion. Let’s also consider that for this automation, there are only two available wires and there is 

no possibility for installing more. As presented in Section 3.2.9, the classical automation circuit 

for the operation of a machine from multiple positions requires three wires, without including the 

wirings for the operation indication in every control position.

A solution to this problem is the utilization of a pulse relay and to apply the automation circuit 

of Figure 3.31. It is obvious that the operation start and pause are achieved by pressing the same 

button. This generates some problems, especially in the case of an operator who is not aware of the 

double operation of this button, and tries to stop the machine, e.g., in an emergency. Moreover, it 

should be noted that the automation circuit of Figure 3.31 has the characteristic of reoperation. If 

such an operation is not desirable, then the automation circuit should be altered as is presented in 

Figure 3.32 with the help of an additional auxiliary relay.

N

C

50 Hz 230 V

R

START/

STOP

START/

STOP

START/

STOP

e

d

d

Control

panel 1

Control

panel 2 

Control

panel n

Figure 3.31  Use of pulse relay for the ON-OFF manual control of a machine from multiple