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Demo:
with:
Test Signal
Specs
Scope Settings
Trigger
Modes
Purposes
a) Firstly calibrate the Oscilloscope to provide a rough view of the signal as in the first example (possible using
Autoset), then set the parameters as indicated above. Endly select "Analyser" mode.
This instructive example uses two highly characteristic signals, a square and a triangle, and through
analysis of harmonics enables verification of the theory of decomposition of fundamental signals.
The Harmonics analysis function does not require calibration of the timebase or sampling speed, but the
vertical sensitivity must be correctly adjusted; the best solution therefore consists in making the calibrations
in Oscilloscope mode beforehand.
This will also provide an approximate verification that the frequency of the fundamental is indeed within the
instrument's admissible limits (40-450Hz for Scopix, OX 6000-II & Handscope, 40Hz-5kHz for Mtx3x5x).
The harmonics can be viewed on 4 channels (Handscope & OX 6000-II : 2 channels), measurements are
made on Vrms and THD (Total harmonic distortion) of the signal for each active channel, and for the
harmonic rank selected, the % of the fundamental, phase in relation to the fundamental, frequency of the
harmonic rank and its RMS value.
b) Return to Oscilloscope mode, check the FFT box, perform an "Autoset" and validate the manual cursors.
In the Horizontal menu we can select the type of scale, Linear or logarithmic FFT, as well as the desired
METRIX Oscilloscope Demo Kit
MTX3x5x SPO &
OX 6000 b)
MTX105x SPO
OX 6000-II
Type
2 signals, one square one triangle
Signal frequency ≈ 50Hz, Vpp ≈ 3.2V (triangle), Vpp ≈ 3.4V (square)
5ms/div - MAIN = 500mV or 1V/div DC coupling
⇑ DC coupling on MAIN, 50% of Vpp for example
"Oscilloscope" mode then "Harmonics", then "FFT"
Use of the "Harmonics" mode to analyse "Power" signals
Comparative use of the Oscilloscope's FFT multi-channel mode
analysis window.
In linear mode the amplitude scale is expressed in
volts, in logarithmic mode in dB, offering a greater
analysis dynamic (49dB for a traditional 8-bit
Oscilloscope, 60dB for the OX6000 and 79dB for
Scopix and its 12-bit conversion.
Contrary to Harmonics Analysis, FFT is not limited to
harmonic ranks of the fundamental, but presents the
whole spectral content of the signal, over the
complete breadth of the Oscilloscope bandwidth.
SCOPIX
HANDSCOPE
no. 14 : Harmonics
Chapter II - 33
a)
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