Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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2-22 Views
SR785 Dynamic Signal Analyzer
Single channel phase is relative to the center of the time record for Uniform, BMH,
Hanning, Flattop and Kaiser windows. For Force and Exponential windows, phase is
relative to the start of the time record. For User windows, the Window Form is user
specified. In general, single channel phase is useful only when the time record is
triggered in phase with the signal.
For two channel measurements, the phase is relative between channel 2 and channel 1.
Triggering is not always required for meaningful two channel phase measurements.
Phase Suppress sets the phase of small data values to zero. This avoids the messy phase
display associated with the noise floor. (Remember, even a small signal has phase.) Set
the Phase Suppress threshold in the [Display Options] menu.
Watch Out For Triggered Sources
If a triggered source is selected (Chirp, Burst Chirp, Burst Noise or Arbitrary), the
triggered measurement phase is stable only if the input signals are derived from the
source output. Turn the source off (or set it to Sine) when making triggered
measurements without the source.
Watch Out For Phase Errors
The FFT can be thought of as a set of bandpass filters, each centered on a frequency bin.
The signal within each filter shows up as the amplitude of each bin. If a signal's
frequency is between exact FFT frequency bins, the filters cause phase errors. Because
these filters are very steep and selective, they introduce very large phase shifts for
signals not exactly on a frequency bin. Use the SR785 source to generate exact bin
frequencies whenever possible.
Unwrapped Phase
Unwrapped Phase view graphs the phase of the measurement data as a continuous
function without ‘wrapping’ around at
±
180 degrees. This view is generally meaningful
only for measurements which have data at every frequency point (such as chirp source or
swept sine).
The phase
θ
is calculated for each point as in the ‘wrapped’ Phase view. The wrapping
starts at the left edge of the display. The value of
θ ±
(n x 360 deg.) which is closest to
the phase of the previous bin is assigned to each bin (n is an integer).
Single channel phase is relative to the center of the time record for Uniform, BMH,
Hanning, Flattop and Kaiser windows. For Force and Exponential windows, phase is
relative to the start of the time record. In general, single channel phase is useful only
when the time record is triggered in phase with the signal.
For two channel measurements, the phase is relative between channel 2 and channel 1.
Triggering is not always required for meaningful two channel phase measurements.
Phase Suppress sets the phase of small data values to zero. This avoids the messy phase
display associated with the noise floor. (Remember, even a small signal has phase.) Set
the Phase Suppress threshold in the [Display Options] menu.