Flicker - Arbiter Systems Portable Power Sentinel 933A Operation Manual

taking the arctangent of the real and imaginary components of the bin
closest to each harmonic. This information cannot be used, however, in the
averaging process described in IEC 61000-4-7, because this specification
requires the rms average of a series of measurements. This, by definition,
requires magnitude data only. Therefore, there are two different harmonic
tables available from the unit. The averaged harmonic data, in accordance
with IEC 61000-4-7, is provided in a 300-element array (6 channels x 50
harmonics), averaged over the interval specified by the user (typically 10
or 15 minutes). The harmonic magnitude and phase data are provided in
a 600-element array, once per second. The harmonic magnitude is the rms
value over the preceding second, and the phase angle is the 'instantaneous,'
absolute (based on a 100 ms window centered at top of second) phase angle,
as described in the preceding paragraph.
9.15

Flicker

Flicker is measured in accordance with IEC 61000-4-15, the successor stan-
dard to IEC 868. Unlike the other measurements described above, flicker
measurement is a continuous process. This process is performed using
a sample rate of 640 samples per second (sps). Anti-alias (decimation)
filtering is performed on the 10240 sps data stream, and the resulting
samples are further processed following the block diagram suggested in
IEC 61000-4-15. The resulting measurements of flicker perceptibility are
classified using a 256-level logarithmic classifier at the full 640 sps rate.
Pst is then determined every ten minutes (or as specified), as described by
the standards.
Although no standards currently require it, the 933A also measures
flicker on the current inputs. This information can be useful in determining
whether a customer's load is causing flicker on the power system, or
whether the customer is being subjected to flicker from other sources. It
is unrealistic to penalize a utility for 'poor power quality' at a customer's
load when the cause of the problem is the load itself.
9.16 Interruptions
Interruptions are monitored on the voltage inputs by comparing the
20/second voltage measurements with a user-supplied threshold. Events
are triggered when the voltage dips below the preset threshold. These can
cause the logging of pre and post-fault data, contact closure, or any of the
other actions described under "Event Logging."
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