Novatech Bitronics M87X Series Manual page 69

Configuration of Hysteresis Settings
For example: Suppose an alarm contact is intended to close when the frequency
exceeds 60.3 Hz. Frequency is generally regulated very tightly about 60 Hz, so except for
the significant transients that the setting is intended to capture, it would not be unusual for
the frequency to dwell for a prolonged time near 60.3 Hz, fluctuating by only an
insignificant amount but crossing the threshold many times (see illustration below, on the
right half of the trace). To eliminate this chatter, the user might configure the hysteresis to
be 0.1 Hz, as shown above. Then if the frequency were to rise from normal to the high
frequency alarm range as illustrated below, the contact will close exactly as it passes 60.3
and it will remain closed until the frequency decreases below 60.2, when the contact
opens.
The hysteresis function operates symmetrically when used with measurements that trigger
below a threshold. So for Event 2 shown in the 70 Series Configurator screen above, a
trigger would occur when the frequency drops below 59.7 Hz, and reset above 59.8 Hz.
Illustration of Trigger and Reset (or Operate and Release) when using Hysteresis
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ML0021 August 15, 2018 Copyright 2018 Bitronics, LLC