Reference Waveform - Tenma 72-7615 Manual

Select the FFT window
• Assuming the YT waveform is constantly repeating itself, the oscilloscope will carry
out FFT conversion of time record of a limited length. When this cycle is a whole
number, the YT waveform will have the same amplitude at the start and finish.
There is no waveform interruption.
• If the YT waveform cycle is not a whole number there will be different amplitudes
at the start and finish, resulting in transient interruption of high frequency at the
connection point. In frequency domain this is known as leakage.
• To avoid leakage multiply the original waveform by one window function to set the
value at 0 for start and finish compulsively. See the following table:
FFT Window
Rectangle
Hanning
Hamming
Blackman
Note: FFT resolution means the quotient of the sampling and math points. When the
math point value is fixed, the sampling rate should be as low as possible relative to the
FFT resolution.
• Nyquist frequency: To rebuild the original waveform, at least 2f sampling rate
should be used for waveform with a maximum frequency of f.
• This is known as Nyquist stability criterion, where f is the Nyquist frequency and 2f
is the Nyquist sampling rate.
Digital Filtering Menu
Functions Menu
Type
Information source
Filtering types

Reference waveform

• Displays of the saved reference waveforms can be set on or off in thee REF menu.
• The waveforms are saved in non-volatile memory and identified with the following
names: Ref A, Ref B.
• To display (recall) or hide the reference waveforms use the following method:
1. Press REF menu button on the front panel.
2. Press F2 to call back.
3. Select the signal source and the position of the signal source 1~10 by use of the
multi-function rotary control.
4. Press REF to display the waveform stored in that location.
Feature
The best frequency resolution, the
worst amplitude resolution. Basically
similar to a status without adding
window.
Frequency resolution is better than
the rectangle window but amplitude
resolution is poorer.
Frequency resolution is marginally
better than Hanning window.
The best amplitude resolution and
the poorest frequency resolution.
Setup
Digital Filtering
Ch1 or Ch2
Lowpass
Highpass
Bandpass
Most suitable measurement item
Temporary or fast pulse. Signal level is generally
the same before and after.
Equal sine wave of very similar frequency. There
is broad-band random noise with slow moving
Sine, cyclical and narrow-band random noise.
Temporary or fast pulse. Signal level varies
greatly before and after.
Mainly for single frequency signals to search for
higher-order harmonic wave.
Digital Filtering
Set CH1 or CH2 as filtering object
Set filter type
9
wave spectrum.
Notes