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Signal Generator
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The signal generator display for the VIPod20 shows the graphs of the 4 signals
being generated. The frequency, amplitude and type of signal can be set
independently from the control panel shown. Sine, square, triangle, ramp and
DC Levels can be generated. Arbitrary waveforms can
be generated using the External setting.
Bar Graph and Panel Meter displays are also available for the signal generator.
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Arbitrary Waveform Generator
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In many test
situations, an arbitrary waveform is required. This can be achieved
using the External
waveform selection of the VIPS software. This takes the waveform
definition from an external file which may be generated using Excel,
other spreadsheet programs or just a text editor.
An external file can also be used
to generate the logic output pattern of the VIPod40 and VIPod50
logic output modules - click here |
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Analog Output - VIPod20 (4ch) VIPod10/20 (1ch) and
VInterface (2ch)
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There
are two ways of externally specifying the analog output using the
VIPod10/20, VIPod20 or Vinterface modules, Point-by-Point
or Piecewise Linear. The two techniques can be mixed on a channel
by channel basis. When External signal is selected from the signal controls,
the external channel controls appear alongside the display rate
control in the top area of the screen. If the position is zoomed,
an explanation of the controls is shown.
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Point-by-Point
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This
technique specifies each point to be outputted. A point-by-point
file is a text file with the extension .dac and can be set up using
Excel. Essentially, the first 4 columns define the 4 channel
signals - Row 1 is the number of points and the rest of the column
is the points (in the range 0 - 4000) defining the signal. Channel
1 (black) and channel 4 (yellow) on the
screen dump were generated by this method.
Both are defined by 640 points.
For VIPods, the output range will depend
on the range connections of the pod. For 0 to 2V and 0 to 4V ranges,
0 count is 0 volts and 4000 count is full scale, i.e. 2.000 or 4.000
volts. For the -2 to 2V range, 0 count is -2.000 volts, 2000 count
is 0 volts and 4000 count is 2.000 volts.
With the Vinterface module, there are 2 channels
and the output goes from 0 count is -5.000 volts, 2000 count is
0 volts and 4000 count is 5.000 volts
This technique gives control of the exact
value at each step but can involve a lot of work generating the
file.
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Piecewise Linear
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This defines a signal as a series of linear segments.
Again, this can be set up using Excel. The initial level, final
level and the number of intervals (at the rate selected from the
screen controls) to go from one level to the other are defined.
The final level of one segment is the initial level of the next
so only 2 values are required to define a each segment except the
last which requires the final value. A step can be introduced by
making the interval count 0 or 1. There will always be an odd number
of points.
For instance, to define a sawtooth signal,
the column could read:-
-5 |
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negative
of number of lines used |
0 |
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starting
level |
1000 |
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running for
1000 counts at selected rate |
4000 |
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up
to a level defined by 4000 (full scale) |
250 |
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running
for 250 counts |
0 |
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down
to a level of 0 (zero scale) |
With a 0 ->4V output selected, this signal
would ramp from 0 to 4V in 1000 counts then ramp back to 0 in 250
counts. In continuous mode, the output will jump from the
last value to the first value at the end of the sequence. In
single-shot mode, the output will sit at the first value until started
and remain at the last value when finished.
This technique is quick to define when only
ramps and steps are involved although curves can be simulated as
shown in channel 3 (white) of the screen
dump. This curve is 640 time steps long
and is defined in 57 lines.
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Operating Modes
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The
operating mode is set from the setup dialog on a channel by channel
basis.
- Continuous - The output runs continually looping back when it reaches
the end of the file. Channels can be synchronised by clicking Sync
on the drop down menu. This sets the position counter of all external
channels to 0 thus returning the signals to the start of the sequence.
- Individual Single-Shot - When single-shot is selected, the signal
may be paused then continued, restarted or reset.
- Group Single-shot - This allows single-shot channels to run synchronously.
On the display, grouped channels are shown by having magenta control
boxes. The controls of all channels assigned to the group are linked.
Clicking any group control changes all group channels.
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Logic Output - VIPod40, VIPod50 and VInterface
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The logic outputs of VIPods40 and 50 and
Vinterface can be set from an external file defined using Excel
or other spreadsheets. The pattern is defined in the 1st column
of the spreadsheet. The 1st row is the number of points in the pattern.
The data is defined by the decimal equivalent of the 8 bit pattern
required - the least significant digit is channel 1.
For example, a cell entry of 172 has the binary equivalent 10101010.
Thus channels 1,3,5 and 7 are logic 0 and channels 2,4,6 and 8 are
logic 1.
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Operating Modes
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There
are 3 operating modes set from the pod drop-down menu.
- Off
- switches external off reverting to manual control.
- Single-shot - runs once
then stops at the end of the pattern. Is controlled in the same
way as the analog output but all 8 channels always work together.
- Continuous - repeats
when it reaches the end of the pattern.
The
logic output pattern can be used to stimulate a circuit in the same
way as a logic analyzer. With a VIPod50, the input section can be
used to monitor the system respose to the
stimulation. |
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