Hameg HM 8131-2 Handbuch Seite 65

STOP
After definition and storage of an arbitrary signal it can
be selected via the main menu like the standard signals.
The basic menu allows to select [Spc] either the signal
stored in the non-volatile 4 k memory or a second signal
stored in the volatile 16 k memory.
TiPP
The second signal (16384 points) is stored in the
volatile 16k memory. It has to be reloaded after the
instrument was turned off.
Generation of arbitrary signals
STOP
Arbitrary signals are stored in a digital memory and consist hence
of steps the amplitude and duration of which have to entered,
also the repition rate. It is important to note that the presence of
sharp steps in the waveform causes high harmonics resp. high
frequencies which can be far above the signal frequency.
Be careful and consider possible effects on your test
circuit by such high frequencies. Add a filter if
necessary.
Amplitude (Y axis) of the arbitrary signal
The vertical resolution is 4096 points total resp. + and – 2048. This
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is equivalent to 12 bits resolution of the output voltage. A signal
with a minimum of – 2047 points and a maximum of + 2047 points
generates maximum output voltage. If the 20 Vpp range was
selected the no load signal would be ±10 Vp.
o = Reference points
of the waveform
1. The points between – 2047 and + 2047 determine the maximum
values as well as the shape of the curve in Y direction. Those
points are relative values only, independent of the actual output
voltage. If an output voltage of 2 V
– 2047 will correspond to – 1 Vp, the point + 2047 to + 1 Vp. If 20
V was selected the respective voltages would be – and + 10 Vp.
pp
2. Should the same curve have been defined with only – 1023 and
+ 1023 points and the output voltage set to 2 Vpp, the point – 1023
would correspond to – 0.5 V, the point + 1023 to + 0.5 V, hence
the maximum amplitude of 2 V
Signal period (X axis) of the arbitrary signal
The resolution in the X axis is equal to that of the Y axis, i.e. 4096
(12 bits) for the first arbitrary signal stored in the 4 k non-volatile
memory and 16384 (16 bits) for the second one stored in the
volatile 16 k memory. The "length" of a point in time is a constant
25 ns (10 MHz signal frequency and 40 MSa/s).
For signal frequencies >10 kHz the resolution will decrease
because not all points will fit any more in one signal period. For
Subject to change without notice
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was e.g. selected, the point
pp
would not be used.
pp
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frequencies <10 kHz the processor calculates the points necessary
to fill one signal period. Vertical points of equal amplitude are
added to the signal. Consequently, at low frequencies a signal
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waveform will consist predominantly of calculated values.
4096 points times 25 ns equals 102.4 µs or a frequency
of 9.765 kHz which is then the optimum frequency as
regards resolution. For 100 kHz e.g. only 1/10 of the
points are used, appr. 410.
TiPP
Reference points
Those points in amplitude and time which the user entered are
called reference points. A waveform will be the more similar to
the desired one the more reference points were entered. However,
it is not necessary to enter very many as the processor will auto-
matically interpolate if that should be acceptable. The interpolated
calculated values will be designated as „calculated" in the
following paragraphs. Both entered and calculated values will be
stored upon leaving the arbitrary editor.
STOP
For signal frequencies >10 kHz the resolution will decrease
because not all points will fit any more in one signal period.
For frequencies <10 kHz the processor calculates the
points necessary to fill one signal period. Vertical points of
equal amplitude are added to the signal. Consequently, at
low frequencies a signal waveform will consist pre-
dominantly of calculated values.
TiPP
1. The length of a signal period is independent of the
number of points and determined solely by the
signal frequency chosen.
2. The point at the beginning (X = 0) is always a reference
value and is automatically given the Y = 0 . The point X = 0
can not be erased, its Y value can be changed using the
STOP
editor.
The arbitrary editor
The HM 8131-2 editor allows to create waveforms or to change
stored waveforms. Before calling the editor it is necessary to
determine first the size (4 or 16 k) of the signal to be edited. All
entries are made via the keyboard supported by the menus.
In order to get to the editor first press the button [menu] in the
main menu. In the main menu 1 go to the function "Arb" and
answer the question "Waveform size".
** WAVEFORM SIZE **
4096 Pts 16384 Pts
This will lead to the entry menu of the editor which offers the
functions: "New", "Edit", "Calc", "Visu":
** 4K ARB MENU ***
New Edit Calc Visu
New
ERASE all date ?
Yes No
This function initializes the selected memory erasing it. Only the
X = O Y = 0 point remains. In order to approve erasing the
Main menu 1 and functions
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