Arbiter Systems Portable Power Sentinel 933A Operation Manual page 129

Sliding Reference
Set the Reference Format to Sliding when you want to follow daily
variations in voltage or current that do not require a trigger unless it
exceeds the expected rate of change.
requirements the line voltage sags during the day and swells during the
night, you might want to use a sliding reference to avoid unnecessary
triggers. A sliding reference would generate a trigger only if the voltage
unexpectedly sags or swells at a rate greater than expected.
Calculating a Sliding Reference Voltage
Per the specification IEC61000-4-30, the sliding reference voltage is
calculated by using equation 7.1; it is of first-order and uses a one-minute
time constant.
(7.1) U = 0.9967
sr(n)
Where
U is the present value of the sliding reference voltage;
sr(n)
U is the previous value of the sliding reference voltage; and
sr(n 1)
U is the most recent 10/12-cycle r.m.s. value.
(10/12)
Note that even though the specification defines the input signal (U) as a
voltage, it has been applied in the 933A to include measured input currents,
as calculated using the same formula, with U as a current.
Logging Time
There are two available settings of which you can choose to control how the
933A logs one-second data when a trigger becomes active: MaxLogTime,
and PostFault.
MaxLogTime: defines the number of seconds to record data during which
the specific trigger is active (i.e. faulted). Setting MaxLogTime to 10
seconds will cause the 933A to record 10, once-per-second records after a
trigger becomes active.
PostFault: defines the number of seconds that the 933A records data
after the trigger becomes inactive (i.e. after the fault has disappeared).
For example, if due to usage
U + 0.0033 U
sr(n 1) (10/12)
111
rms