Reference Multimeter and 8 ½ Digit Multimeter
Functions
43
(Measure Setup): A 100 kHz or 3 MHz low pass filter or Filter Off can be
selected and the aperture is set in this setup menu. The low pass filter is inserted
after the signal conditioning and before the high-speed analog-to-digital
converter. The default is 3 MHz. The aperture of the analog-to-digital converter
has a default of 0 ns, so the analog-to-digital converter digitizes the input at the
time of the trigger. The entire process for one reading is 200 ns, which gives a
maximum trigger rate of 5 MHz. The aperture can be set from 0 ns to 3 ms in
200 ns increments up to 1 ms, and 100 μs increments from 1 ms to 3 ms.
Digitizing Examples
1) This simple example captures 1 000 000 readings and then shows the
resulting signal using Analyze. From a power-on default state:
1. Push .
2. Select the 10 V range with the (Range) softkey.
3. Push and set Triggers/Arm (Count) to 1000000.
4. Push to return to the Digitize menu.
5. Apply a 10 V, 10 Hz sinewave signal to the input.
6. Push to capture the signal.
7. Push to see two cycles of the captured signal.
2) Capture 10 000 samples of a 10 Vrms 10 kHz signal with at least 0.01 %
accuracy:
Considering the Nyquist theory for post process transformation of data into
the Frequency domain, you need to sample at least twice the frequency of
the signal, you should set the sample rate to 20 kHz or higher. Referring to
the Product specifications, 50 kHz meets the accuracy requirement and is
faster than twice the signal, so this is a good choice. See Specifications. To
set the Trigger subsystem, push (). You can indirectly set the
sample rate with the Trigger subsystem TIMER. If the TIMER interval is
longer than other delay settings in the Trigger subsystem, the trigger rate is
the reciprocal of the TIMER interval. The aperture time should be less than
the sample period to avoid “trigger too fast” errors. "Trigger too fast" errors
can result in an unexpected number of readings that different from the trigger
count setting. In this example, set the aperture period to 10 μs, ½ the period
of 50 kHz. Aperture is set with (Measure Setup) in the Digitize top
menu. See Table 11.
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