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7 - Programming the DC Source
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When the instrument is turned on and at *RST, the output voltage or current sampling rate is 15.6
microseconds, and the sweep size is set to 2048 data points. This means that it takes about 32
milliseconds to fill up 2048 data points in the data buffer. Adding a command processing overhead of
about 20 milliseconds results in a total measurement time of about 50 milliseconds per measurement.
You can vary this data sampling rate with:
SENS:SWE:TINT <sample_period>
SENS:SWE:POIN <points>
For example, to set the time interval to 46.8 microseconds per measurement with 1500 samples, use
SENS:SWE:TINT 46.8E-6;POIN 1500.
Note that reducing the number of sample points increases the speed of the measurement; however, the
tradeoff is greater measurement uncertainty in the presence of noise..
Window Functions
The dc source lets you select from two measurement window functions: Hanning and Rectangular. To
select a window function, use:
SENS:WIND: HANN | RECT
As shipped from the factory, the dc source measurement functions use a Hanning window. The Hanning
window applies a cos
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weighting function to the data in the measurement buffer when computing average
and rms measurements. This returns accurate data even if an integral number of waveform cycles are not
captured, provided that at least three or more waveform cycles are in the measurement buffer. If there are
only one or two waveform cycles, the Hanning window will not give accurate results.
With a Rectangular window, no weighting function is applied to the data in the measurement buffer.
However, to use the Rectangular window function to return accurate data for one or more waveform
cycles, an integral number of waveform cycles must be captured in the measurement buffer. This means
that you must accurately know the waveform period beforehand. In this way you can chose the sample
interval and the number of data points so that an integral number of waveform cycles will end up in the
measurement buffer.
Measuring Output 2 Voltage and Current (Agilent 66319B/66319D only)
The measurement parameters for output 2 are not programmable. They are fixed at 2048 data points with
a 15.6 microsecond sampling rate using a Hanning window. To measure the average output voltage or
current for output 2, use:
MEAS:VOLT2?
MEAS:CURR2?
Making Enhanced Measurements
Agilent Models 66321B/D and 66319B/D have the ability to make several types of voltage or current
waveform measurements. These expanded measurement capabilities are particularly useful for loads that
draw current in pulses. The SCPI language MEASure and FETCh queries are used to return the various
measurement parameters of voltage and current waveforms.