Defining An Arbitrary Function; Fig. 4.6: Arbitrary Example; Under The Menu Point Built-In Waveforms You Can - Hameg HMF2525 Handbuch

O p e r a t i o n o f t h e H M F 2 5 2 5 / H M F 2 5 5 0
4.7

Defining an arbitrary function

Fig. 4.6: Arbitrary example

In addition to the predefined waveforms the HMF2525 / HMF2550
allows to generate user-defined waveforms. However, there
are some rules and specification limits to be observed which
will be described.
The arbitrary signals are digitally generated and can hence
be defined with great accuracy. The frequency and amplitude
of the waveform thus generated can be varied. Apart from the
limitations given by the specifications it should be kept in mind
that waveforms freely defined and digitally generated may con-
tain high frequency harmonics far above the signal frequency.
When using arbitrarily defined signals their possible effects on
the circuits tested should be evaluated.
An arbitrary waveform may be selected from the predefined
waveforms, imported via front USB stick in CSV format (load
curve via Non
volatiles
loaded via interface from the HMExplorer software. Further-
more, pre-loaded waveforms will be stored in the internal
memory permanently.
The CSV file must be defined that the actual number of
point is seperated with a comma ( , ) from the amplitude
value. The decimal icon of the amplitude value is a point (
. ). Each pair of values (number of points, amplitude value)
must be separated with an ENTER (CR + LF) from each
other. The amplitude values must be located between -1
and +1 (e.g. +1 means a 100% amplitude value, starting
from the zero line up to the positive max. value). The
number of points amounts max. 256000 points.

Under the menu point Built-in waveforms you can

find different signal types, which can be selected with the knob:
– Sine / Square Function
– Positive / Negative Ramp Function
– Triangle Function
– White / Pink Noise Function
– Cardinal Sine
– exponential rise / fall
The HMF unit can display an arbitrary waveform preview
with 250 points. This is related to the resolution of the
display. With more than 250 arbitrary points the waveform
preview may differ from the original waveform.
38
Subject to change without notice
waveforms) or can be
The HMF2525 / HMF2550 offers an internal memory of 4MPts
for arbitrary signals. Once a waveform has been defined it
can be stored in an EEPROM (non-volatile memory) and used
like any predefined one. Stored signals can be selected via
the internal file browser (load curve via Non volatiles
waveforms).
4.7.1 Building a user defined arbitrary waveform
– Create a CSV file with Microsoft Excel, the free of charge
available HMExplorer software (www.hameg.com) or with
an oscilloscope.
– Save the data as CSV file to the root directory of a FAT or
FAT32 formatted USB stick.
– Connect the USB Stick to the front side USB connector of the
device and load the file via the softkey Non volatiles
waveforms (page 2|2) into the instrument
– With the softkey button Save (or Copy with internal file
browser), the stored waveform could now transfered from
RAM to ROM memory of the function generator; file name
and comment can be given.
If a large waveform with high frequency is displayed, the instru-
ment has to interpolate the arbitrary points, which is done
according to a specific algorithm. As described in the data sheet
the HMF can handle arbitrary waveforms with 250 MSa/s. This
corresponds to a minimum dwell time of 4ns per arbitrary point.
Therefore, an arbitrary waveform with 256.000 arbitrary points
results in a maximum frequency of 976.56Hz. Consequently, at
higher frequencies the number of arbitrary points must be
reduced.
The function generator works on binary coded base. The-
refore, the arbitrary waveforms have to be a multiple of
128, 256, ... etc. If this multiple is not obeyed, the instru-
ment will interpolate to the next possible multiple of 2^x.
If a waveform is transmitted by the HMExplorer software, it will
be stored into the RAM first. To store this waveform continously,
please transfer it into the ROM. Same procedure is valid for CSV
files transferred by the front USB connector. Once transferred
into the instrument, waveform data can not be edited anymore.
4.7.2 Example for a user defined arbitrary wave-
form
Creation with Excel (CSV)
The easiest way to create a user defined arbitrary waveform is
Excel. After entering the arbitrary values the file is saved as
CSV. A short example will illustrate the configuration of this
CSV file.
1, 0.00
2, 0.33
3, 0.67
Column 1 = arbitrary point
4, 1.00
5, 0.67
Column 2 = amplitude value (0.1 corre-
6, 0.33
sponds an amplitude value of 10%)
7,
0.00
8, -0.33
Column 1 will be separated with a „ , „
9, -0.67
(comma) from column 2. The decimal
10, -1.00
point for the amplitude value is a „ . „
11, -0.67
(point).
12, -0.33
13, 0.00