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Operating the Power System 4
Series N6700 User’s Guide 71
To offset the beginning of the acquisition buffer relative to the
acquisition trigger, use:
Front Panel: SCPI Command:
Select Measure\Sweep.
Enter an offset value and press
Select.
To offset the measurement on
channel 1 by 100 points use:
SENS:SWE:OFFS:POIN 100,(@1)
With a negative offset, values at the beginning of the buffer represent
samples taken prior to the trigger. When the value is 0, all values are
taken after the trigger. Values greater than 0 can be used to program
a delay time from the receipt of the trigger until the values entered
into the buffer are valid. (Delay time = offset x sample period).
NOTE
If, during a pre-trigger data acquisition, a trigger occurs before the pre-trigger
data count is completed, the measurement system ignores this trigger. This will
prevent the completion of the measurement if another trigger is not generated.
Specify a Window Function
Windowing is a signal conditioning process that reduces the error in
average measurements made in the presence of periodic signals and
noise. Two window functions are available: Rectangular and
Hanning. At power-on, the measurement window is Rectangular.
The Rectangular window calculates average measurements without
any signal conditioning. However, in the presence of periodic signals
such AC line ripple, a Rectangular window can introduce errors
when calculating average measurements. This can occur when a non-
integral number of cycles of data has been acquired due to the last
partial cycle of acquired data.
One way of dealing with AC line ripple is to use a Hanning window.
The Hanning window applies a cos
4
weighting function to the data
when calculating average measurements. This attenuates the AC
noise in the measurement window. The best attenuation is achieved
when at least three or more waveform cycles are in the measurement.
TRIGGER
4096 DATA POINTS
4096 DATA POINTS
4096 DATA POINTS
OFFSET = -4095
OFFSET = -2048
OFFSET = 0
4096 DATA POINTS
OFFSET = 0 to 2
9
TIME