Why can one not see a duration time for a sag event?

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Issue:
A sag event has occurred on an ION or PowerLogic meter, but the duration does not display through a data log viewer.

Product Line:

Power Monitoring Expert 7.2

Power Monitoring Expert 8.x

Power Monitoring Expert 9.x

Power Monitoring Expert 2021

Power Monitoring Expert 2022

Power Monitoring Expert 2023

Power Monitoring Expert 2024

Environment:
Vista

Cause:
All meter power quality events (sag, swells, transients) have two separate 'Disturbance Start' and 'Disturbance End' timestamps. PME uses the difference between these two to calculate the duration. During a sag event, if a meter's control power is wired in parallel to the voltage inputs this can cause the meter to only register the 'Disturbance Start' event.

Resolution:
If a duration time stamp is needed, the meter should be wired with separate control power from the voltage inputs such as a battery backup. This will ensure that if the voltage inputs go to zero, the meter will remain powered to capture both the start and end events.