CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

This operating mode is very useful; as an example suppose you want to measure the
total harmonic distortion of a sinusoidal signal while displaying also its frequency
content. To do this lets invoke the FFT and Multi-meter control panels together; then
press the Go button in FFT, this will start both measurements (see also 8.6 about this);
inside the Multi-meter select the THD parameter and then press the minimized button.
You should obtain a measurement situation like the one in Fig.8.3. In this figure we were
acquiring directly the output of CLIO while generating a 1kHz sinusoid at 0dBu.
Figure 8.3
8.3.3 CAPTURING THE GLOBAL REFERENCE LEVEL
Let's see now how to capture a level to be the reference for other measurements. Once
this is done then the subsequent measures done in all the instrument, with the units
dBRel selected, will refer to it. As an example we go back to the procedure described
in 3.5.1 which aims at validating a calibration. This is substantially the measurement
of the frequency response of the CLIO board itself which is, when calibrated, a straight
line; as said in the cited procedure the acquired level of such a measurement is -5.2 dBV.
Let's see a practical way to acquire this level in order to refer future measurements to
it. Maintain the instrument connected as in Fig.3.9, with input A and output A short
circuited. Press the MLS button to start generating the MLS signal (the same that MLS
uses during its operation). Press Go to start acquiring this signal, you should read circa
0.54V. Select also the Slow integration as the MLS signal is a wide band noise. While
the measurement is running press the button; answering yes to the warning
message you'll set the global reference level. To inspect the captured value press the
button's drop down menu. You should see the situation in Fig.8.4.
Figure 8.4
The drop down tells you what is the actual global reference level. If you want to restore
the default , which is 1V, just choose Reset. Should you choose now, as reading units,
dBRel expect to read 0dBRel!
72 Chapter 8 - Multi-Meter