Introduction

A power interruption, such as a breaker trip, can sometimes leave a safety controller in an unexpected state upon restart. This article explains how to identify and resolve a condition where a G9SP safety PLC remains in Idle mode after power is restored.

Reported Condition

The issue typically presents with the following:

• A breaker trip occurred, interrupting power to the G9SP safety PLC system
• After power is restored:
  • MS (Module Status) LED is flashing green
  • LOCK LED is flashing yellow
  • Both LEDs may flash simultaneously

Understanding the LED Indicators

According to the G9SP Operation Manual:

• MS flashing green indicates that the safety PLC is in Idle mode and not executing the safety program
• LOCK flashing yellow indicates that the configuration is valid but currently unlocked

This combination confirms that the controller is not running, even though the configuration itself is intact.

For detailed reference, consult the G9SP manual:

https://www.omron.com.au/data_pdf/mnu/z922-e1-12_g9sp.pdf?id=2937

• Page 40 – Operation indicators
  
• Page 168 – Changing operating mode (Idle to Run)
  
• Page 169 – Configuration lock settings
  

Resolution

To restore normal operation, the controller must be placed back into RUN mode.

Before commencing any reprogramming make sure the proper risk assessments/JSA/SWMS have been completed on the machine/parts to be controlled to prevent damage to machine and/or injury.

Step 1 – Confirm Programming Access

Determine whether you have access to the safety program using the appropriate configuration software. If programming changes were previously made, ensure the latest version is available.

Step 2 – Change to RUN Mode

• Connect to the G9SP controller using the configuration tool
• Navigate to the operation mode settings
• Change the mode from IDLE to RUN

Refer to Page 168 of the manual for detailed instructions.

Step 3 – Lock the Configuration (If Required)

If the system requires a locked configuration for operation:

• Apply the configuration lock after confirming correct operation
• This ensures the safety program cannot be modified unintentionally

Refer to Page 169 of the manual for guidance.