Status LED lights are located on the front of the PLC’s CPU module and other modules. 

For most PLCs, the status lights give you relevant information, such as whether the PLC is in RUN mode, the back-up battery is functioning, and which input or outputs are true or ON. 

The status light does just what the title says – it gives the status or position of the PLC at any given time, which is usually displayed with an LED. 

Other purposes for the PLC status light may include: 

1. Power ON, 

2. Program running, 

3. Fault (generally is displayed when the PLC has experienced a major software or hardware problem).

4. Stop Status

5. Battery Status

6. Trip Status

7. Program Copy

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