Omron NT31 Operation Manuals page 239

System Maintenance
Checking the RUN LED
228
S If the buzzer functions correctly, it will sound continuously. At this time, the
"Buzzer Check" touch switch will be displayed in reverse video.
S To stop the buzzer while it is sounding, press the "Buzzer Check" touch switch
again.
Check if the RUN LED functions normally.
Check the RUN LED by following the menu operation from the System Menu
shown below.
Select "Device Check".
Select "Buzzer Check".
Select "Maintenance Mode".
Select "I/O Check".
Section 6-11