Low voltage LU, entry in history buffer

Question:

Untder which conditions is the message 'Low voltage LU' entered in the history buffer.

Answer:

The message 'Low voltage LU' is entered in the history buffer, if

• the power (mains or DC supply) is switched off for less than 3 sec. (more precisely: the DC bus voltage drops for less than 3 sec. under the switch-on threshold LU) and
• the control board of the controller is still in operation before the supply voltage is reconnected (occurs particularly with separate supply of the control control with 24 V (X5/59) or controllers with large power).

If the LU threshold is not reached for more than 3 sec. no entry is created. This case is interpreted as desired mains switching and not as fault.

Further information can be obtained from the systems manuals of controllers 9300 in tab D, section 'Monitoring'' (low voltage LU).

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