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Power Quality Analyzer Model 3945-B
95
Hysteresis
Hysteresis is a ltering principle, often used after the threshold detection has
occurred. A correct setting of hysteresis value will avoid repeated triggering when
the measure is varying close to the threshold.
The event detection is activated when the measure is going over the threshold but
it can only be deactivated if the measure goes under the threshold minus the value
of the hysteresis.
The default hysteresis value is 2% of the reference voltage but it may be set in the
range of [1%, 5%] depending of the voltage stability on the system.
Alarm for high voltage RMS (Swell Detection)
Hysteresis =
2% Uref
Swell duration
Threshold of swell =
100% Uref
Level to go back =
100% - 2% = 98% Uref
Alarm for low voltage RMS (Sag or Interruption Detection)
Hysteresis =
2% Uref
Level to go back =
(100% + 2%)Uref
Threshold = 102% Uref
Duration