Chapter 5: Using the Web Interface
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Example: When Hysteresis is Useful
This example demonstrates when a deassertion hysteresis is useful.
The current critical threshold for the inlet is set to 19 amps (A). The current
draw rises to 20A, triggering a Current Critical alert. The current then
continues to fluctuate between 18.1A and 20A.
With the hysteresis set to 1A, Dominion PX continues to indicate that the
current on the inlet is above critical. Without hysteresis (that is, the
hysteresis is set to zero), Dominion PX would de-assert the condition each
time the current dropped to 18.9A, and re-assert the condition each time
the current reached 19A or higher. With the fluctuating current, this could
result in a number of repeating SNMP traps, and/or an e-mail account full
of repeating SMTP alert notifications.
Example: When to Disable Hysteresis
This is an example of when you want to disable hysteresis for the inlet.
Hysteresis is disabled when its value is set to zero.
The upper warning threshold for current in the inlet is set to 15A. In normal
usage, the inlet draws 14.6A of current. A spike in demand causes the
current to reach 16A, triggering an alert. The current then settles to the
normal draw of 14.6A.
With the hysteresis disabled, Dominion PX de-asserts the condition once
the current drops to 14.9A. Otherwise the inlet would still be considered
above the warning threshold as long as the current never dropped to
14.0A. The condition would not de-assert, even if the current returned to
normal.
What is Assertion Timeout?
When the assertion timeout is enabled, the Dominion PX device asserts
any warning or critical condition only after a specified number of
consecutive samples that cross a particular threshold are generated. This
prevents a number of threshold alerts from being generated if the
measurements return to normal immediately after rising above any upper
threshold or dropping below any lower threshold.
