ABB RELION 670 Series Technical Manual page 110

Section 5
Local Human-Machine-Interface LHMI
Input function
All function keys work the same way: When the LHMI is configured so that a certain function
button is of type CONTROL, then the corresponding input on this function block becomes active,
and will light the yellow function button LED when high. This functionality is active even if the
function block operation setting is set to off. It has been implemented this way for safety reasons;
the idea is that the function key LEDs should always reflect the actual status of any primary
equipment monitored by these LEDs.
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1MRK 502 066-UUS B
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Technical manual