Can you explain how the PQube 3 detects and trigger events such as sags/swells?

For detecting events, the PQube3 uses the RMS½ method per IEC 61000-4-30 (standard which defines how meters should evaluate power quality parameters). RMS½ is "the value of the RMS voltage measured over 1 cycle, commencing at a fundamental zero crossing, and refreshed every half-cycle."

The PQube 3 is constantly watching the 1-cycle RMS voltage every half cycle. As soon as this RMS value exceeds the voltage dip or swell threshold, the PQube 3 will record and trigger an event. The dip and swell thresholds are defined as a percent of nominal voltage remaining.

For example, your nominal voltage is set to 120V RMS, and your dip threshold is 90%. When the voltage dips to 108V, the PQube 3 will detect a voltage sag event. The event ends when the voltage goes above the threshold +/- any hysteresis.