Cycle to Cycle Waveshape
This method breaks down the present AC waveform
being measured into user defined windows of time
(shown below in the circle) that represents a
percentage of the overall waveform. Each window is
compared to the same window of time in the previous
waveform, and if the difference exceeds the user’s
limits, an event is recorded. In the picture below, the
duration (width of the window) is 10% (1.67ms @60Hz),
which means the waveform is broken down into 10
consecutive windows, with each representing 10% of
the overall waveform. If the duration were 50%, the
waveform would be broken down into 2 windows, with
each representing 50% (8.3ms) of the overall
waveform.
RMS distortion (or difference) waveshape
This method performs a (sample) point-by-point
subtraction of the previous waveform from the present
waveform. If the waveforms are the same, the
difference will be zero; otherwise the difference will
be the change in waveshape from the previous to
present waveform. If the difference exceeds the
customer’s limits, an event is recorded.
High Speed Sampling –
Xplorer, Xplorer-400
High frequency detected transients use special
circuitry to detect and capture transients as small as 1
microsecond in duration. These transients can be
positive and/or negative values above or below the low
frequency waveshape.
Magnitude of Supply 200ms Window
IEC 61000-4-30 and IEC 61000-4-7 require data be
acquired over a 200ms window for use in certain
measurements, such as magnitude of supply,
harmonics, and interharmonics. The 200ms window
equates to 12 cycles at 60Hz and 10 cycles at 50hz. A
10 cycle 50Hz example is shown below. In addition,
Class A compliance requires the 200ms windows to be
gapless, meaning that any processing by the
instrument must be completed in time to process the
next 200ms window without any gaps between
windows. Being Class A, the Dranetz HDPQ family fully
complies with these requirements.
Harmonics & Interharmonics
Harmonic & Interharmonic computations are in
accordance with IEC 61000-4-7 and IEEE 519, which
dictate that harmonic analysis is done using a
synchronous 200ms window of 10 cycles for 50Hz, or 12
cycles for 60Hz. Successive 200ms windows are
gapless. This results in frequency bins that are
nominally 5Hz wide. The actual width of the bin is
equal to the actual frequency divided by 10 if the
nominal frequency is 50Hz, and 12 if 60Hz. For
example, if the actual frequency is 49.9 Hz, the bin is
4.99Hz, but is labeled “5Hz”.
All harmonic based triggering of the Dranetz HDPQ is
based upon the (DFT) harmonic analysis and
computations of each 200ms magnitude of supply
window. Results are used for all harmonic parameters,
computations and triggers. Therefore, 200ms is the
smallest unit of measurement for harmonic type
parameters and is the basis for all associated min,
max, and average measurements.
Harmonic parameters include:
VTHD, ITHD, VTID, ITID, K-Factor, TIF, TDF, User
Specified (individual) Harmonics, Mains Signaling
Frequencies, and other parameters.
Please see the parameter list below for a complete list
of parameters.
Voltage Flicker
Voltage Flicker computations are in full compliance
with IEC 61000-4-15 and IEEE 1453. Flicker is a
phenomenon due primarily to small, rapid fluctuations
of the voltage. Loads that exhibit continuous, rapid
variations in the load current, particularly the reactive
component, can cause voltage variations, often
referred to as flicker. Flicker is characterized by
modulation at a frequency that is typically less than
25Hz. Modulating signal magnitudes as low as 0.5% of
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