Introduction to Industrial Automation

Figure 3.3  Motor operation with thermal overload protection.

C

230 V 50 Hz 

N

Stop

Start

C

C

e

R

e

C

Machine

operation

indicator

Overload fault

indicator

Temperature

fault siren

Temperature

sensor contact

 

Figure 3.4  Signaling of machine operation or faults.

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  Introduction to Industrial Automation

operation information is needed directly from the motor itself, special sensors can be utilized to 

provide this.

Different types of light indicators can also display the various faults in the operation of a 

machine. The most common indication of a fault is the activation of a thermal overload relay due 

to an overcurrent situation for an extended period of time (Figure 3.4), which is called a “thermal 

overload trip”. In cases where the fault is of a high risk or very dangerous, the light indication can 

be accompanied by proper sound indications (sound alarms) through the utilization of a horn or 

a buzzer.