Medical ScopeMeter
How to Use the Test Tool
17
Mathematic Function Spectrum (FFT)
The Spectrum function shows the spectral content of the input A, B, C or D waveform in the input
waveform color. It performs an FFT (Fast Fourier Transform) to transform the amplitude
waveform from the time domain into the frequency domain. To reduce the effect of side-lobes
(leakage) it is recommended to use Auto windowing. This will automatically adapt the part of the
waveform that is analyzed to a complete number of cycles. Selecting Hanning, Hamming or no
windowing results in a faster update, but also in more leakage. Ensure that the entire waveform
amplitude remains on the screen.
To use the Spectrum function, do the following:
1. Press
P
to show the SCOPE key labels.
2. Open the WAVEFORM OPTIONS menu with
4
.
3. Use the cursor and
E
to:
a. Highlight
Waveform:
b. Select
Mathematics...
to open the Mathematics.
c. Select
Function:
Spectrum
.
d. Select
Window: Auto
(automatic windowing),
Hanning
,
Hamming
, or
None
(no
windowing).
Observe that the top right of the screen shows SPECTRUM. See
. If it shows LOW
AMPL a spectrum measurement cannot be done as the waveform amplitude is too low. If it
shows WRONG TB the time base setting does not enable the test tool to show an FFT result. It is
either too slow, which can result in aliasing, or too fast, which results in less than one signal
period on the screen.
4. Press
1
for spectrum analysis on waveform A, B, C or D.
5. Press
2
to set the horizontal amplitude scale to linear or logarithmic.
6. Press
3
to set the vertical amplitude scale to linear or logarithmic.
7. Press
4
to toggle the spectrum function between off or on.
