Introduction to Industrial Automation

Figure 3.2  Machine operation (a) manually or (b) automatically via sensor command.

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Industrial Automation Synthesis 

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3.2.2   Operation and Fault Indication

The indication that a machine is in operation can be achieved simply either by the sound produced 

from the operated machine or by a visual inspection of its moving parts. However, it is straight-

forward that both ways for indicating the operation of the machine are not accepted, not only 

because they are old-fashioned but also because these approaches are ineffective, e.g., in the case 

that the operator is away from the operating machine. As a design regulation, the operation of 

the machine is indicated through the utilization of indicative lamps that are placed on the control 

panel. This control panel can be located either on the machine or at a distance from it.

A lighted indicator is able to inform the operator that the corresponding machine is in opera-

tion. However, in reality, the exact information that the light indication is providing is that “the 

power relay in energized”, as displayed in Figure 3.4. For example, in a case where the power cable 

from the power relay to the motor is cut, independently of the fact that the light indication will 

be on, the motor will not be in operation. In the majority of applications, the light indications of 

the machines’ operation are implemented in the form of Figure 3.4. In special cases, where the 

NC contact of

overload relay

R

N

RS

C

230 V 50 Hz 

R

N

Stop

Start

C

C

e

230 V 50 Hz 

e