USBee AX Oscilloscope
The USBee AX Oscilloscope functions as a standard Digital
Storage Oscilloscope, which is a tool used to measure and display analog
signals in a graphical format. It
displays what the analog signal input is doing over time. This section details the operation of the Oscilloscope
application that comes with the USBee AX.
Below you see the application screen.
Oscilloscope Specifications
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Analog
Inputs
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2
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Analog
Channels
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1
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Maximum
Analog Sample Rate [1]
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16 Msps
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Analog
Bandwidth
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8 MHz
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Input
Impedance
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1M Ohm/30 pF
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Input
Voltage Range
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-10V to +10V
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Analog
Sensitivity
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78mV
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Analog
Resolution
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256 steps
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Channel
Buffer Depth [2]
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>1 Million
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Volts
per Division Settings
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100mV to 5V in 6 steps
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Time
per Division Settings
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100ns
to 2s in 23 steps
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Trigger
Modes
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Auto, Normal, Single
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Trigger
Voltage
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Between -10V and +10V
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Cursors
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2 Time and 2 Voltage
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Voltage
Display Offset
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Up to maximum inputs
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Time
Display Offset
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Up to available buffer depth
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Trigger
Position Setting
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10% to 90%
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Measurements
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Min, Max, Top Bottom, Freq, Period
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Reference
Waveform
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Save and compare
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Features
Pod Status
The Oscilloscope display shows a current USBee AX Pod Status by a red or green LED. When a USBee AX is connected to the computer,
the Green LED shows and the list box shows the available Pod ID List for all of the USBee Axs that are connected. You can choose which one you want to
use. The others will be unaffected. If a USBee AX is not connected, the LED will
glow red and indicate that there is no pod attached.
If you run the software with no pod attached, it will run
in demonstration mode and simulate data so that you can still see how the
software functions.
Channel Control
You can choose which channel will be captured and displayed
by pressing the CH1 or CH2 button. The
next trace shown will be from that new analog channel.
Run Control
The Oscilloscope captures the behavior of analog signals
and displays them as a trace in the waveform window. The Run Control section of the display lets
you choose how the traces are captured.
Below is the Run Control section of the display.
The left button is the Run/Stop
control. When the oscilloscope is first
started, the Run button is pressed. This
Run mode performs an infinite series of analog traces, one after the
other. This lets you see frequent
updates of what the actual signal is doing in real time. If you would like to stop the updating, just
press the Stop button and the updating will stop. This run mode is great for signals that
repeat over time.
The Single
button captures a single trace and stops.
This mode is good for detailed analysis of a single event, rather than
one that occurs repeatedly.
The Buffer Size
lets you select the size of the Sample Buffer that is used. For each trace, the buffer is completely
filled, and then the waveform is displayed.
You can choose buffers that will capture the information that you want
to see, but remember that the larger the buffer, the longer it will take to
fill.
You can also choose the Sample Rate that you want samples taken. You can choose from 1Msps (samples per
second) to up to 16 Msps. The actual
maximum sample rate depends on your PC configuration. You can run the menu item Setup | Sample Rate
Test to determine the maximum sample rate for your system.
Trigger Settings
The Oscilloscope uses a Trigger mechanism to allow you to
capture just the data that you want to see.
You can specify the trigger voltage level (-10V to +10V) by using the
slider on the left hand side of the waveform display. A red line that indicates the trigger level
will momentarily be shown as you scroll this level. A small T will also be shown on the right hand
side of the screen (in the cursors bar) that shows where this level is set to.
The waveforms are shown with a trigger position which
represents where the trigger occurred.
This sample point is marked on the waveform display with a Vertical red
dotted line and a T in the horizontal cursors bar.
This trigger position is where the waveform crossed the Trigger Voltage level that you have
set. To move the trigger voltage level,
just move the slider on the left of the waveform.
You can also specify if you want the oscilloscope to
trigger on a Rising or Falling Edge. Below shows a trace captured on each of the
edges.
 
Trigger Slope = Rising Edge Trigger
Slope = Falling Edge
The Trigger position is placed where the actual signal
crosses the trigger voltage with the proper slope. The USBee AX allows for huge sample buffers,
which means that you can capture much more data than can be shown on a single
screen. Therefore you can scroll the
waveform back and forth on the display to see what happened before or after the
trigger.
You can use the Prestore
setting to specify how much of the data that is in the sample buffer comes
before the actual trigger position. If
you place the Prestore all the way to the left, most of the samples taken will
be after the trigger position. If you
place Prestore all the way to the right, most of the samples taken will be
before the Trigger position. This
control lets you see what actually happened way before or way after the trigger
occurred.
The Auto and Normalmodes specify how the screen is to behave if the trigger voltage level you set
is outside the range of the actual signal you are measuring. In Normalmode, the screen will only update when the
measured signal actually crosses the trigger level. In Auto
mode, the display will periodically update even if the waveform does not cross
the trigger level. This allows you to
see what is happening on the display even if you have an incorrect trigger
level set. If the trigger level is set to
a level that is within the actual range of the measured signal, then Auto and Normalfunction the same.
The little Triggered
LED on the display will glow green when the trigger condition has been
met. It will glow red when the trigger
condition has not been met.
Waveform Display and Zoom Settings
The Waveform display area is where the measured signal
information is shown. It is displayed
with time increasing from left to right and voltage increasing from bottom to
top. The screen is divided into Divisions to help in measuring the
waveform. The amount of Volts per
division and the amount of Seconds per Division are displayed in the top left
of the display.
The position of the waveform defaults to show the actual
trigger position in the center of the screen.
However, you can move the display to see what happened before or after
the trigger position.
To Scroll the Waveform
in Time left and right, you can use the scroll bar at the top of the
waveform display, or you can simply click and drag the waveform itself.
To Scroll the Waveform
in Voltage up and down, you can use the scroll bar at the right of the
waveform display, or you can simply click and drag the waveform itself.
To change the number of Seconds per Division or the number of Volts per Division, use the knobs at the bottom of the display. Simply click the knob and drag to the desired
setting. You can also zoom in and out in
time by clicking on the waveform. To
zoom in, click the left mouse on the waveform window. To zoom out in time, click the right mouse
button on the waveform window.
The Display section of the screen shows three selections
that affect the way the waveform is displayed.
The Wide setting
shows the wave using a wider pixel setting.
This makes the wave easier to see.
The Vectors
setting draws the waveform as a line between adjacent samples. With this mode turned off, the samples are
shown simply as dots on the display at the sample position.
The Persist mode
does not clear the display and writes one trace on top of the other trace.
The benefits of these display modes can be seen when you
are measuring fast signals and want to get more resolution out of the
oscilloscope than the maximum sample rate allows. See the below traces to see the difference. Each trace is taken of the same signal, but
the right one shows much more wave detail over a short time of display updates.
 
Persist = OFF, Vectors = ON, Wide = ON Persist = ON, Vectors = OFF, Wide
= ON
Measurements and Cursors
The main reason for using an
oscilloscope is to measure the various parts of a waveform. The USBee AX uses cursors to help in these
measurements.
The X1 and X2
Cursors are placed on any horizontal sample time. This lets you measure the time at a specific
location or the time between the two cursors.
To place the X cursors, move the mouse to the gray box just below the
waveform. When you move the mouse in
this window, you will see a temporary line that indicates where the cursors
will be placed. Place the X1 cursor by
left clicking the mouse at the current location. Place the X2 cursor by right clicking the
mouse at the current location.
The Y1 and Y2
Cursors are placed on any vertical voltage level. This lets you measure the voltage at a
specific location or the difference in voltage between the two cursors. To place the Y cursors, move the mouse to the
gray box just to the right of the scroll bar to the right of the waveform. When you move the mouse in this window, you
will see a temporary line that indicates where the cursors will be placed. Place the Y1 cursor by left clicking the
mouse at the current location. Place the
Y2 cursor by right clicking the mouse at the current location.
In the Measurement window,
you will see the various measurements made off of these cursors.
· X1
Position time at the X1 cursor relative to the trigger position
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X2
Position time at the X2 cursor relative to the trigger position
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dX
time difference between X1 and X2 cursors
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1/dX
the frequency or the period between X1 and X2 cursors
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Y1
Position voltage at the Y1 cursor
relative to Ground
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Y2
Position voltage at the Y2 cursor
relative to Ground
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dY
voltage difference between Y1 and Y2 cursors
There are also a set of automatic measurements that are
made on each trace. These are calculated
without the use of the cursors. These
are:
· Max
the maximum voltage of all samples in the current trace
·
Min
the minimum voltage of all samples in the current trace
·
Top
the average of the top of the waveform
·
Bottom
the average of the bottom of the waveform
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Freq
the frequency of the signal currently shown on the screen
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Period
the period of the signal currently shown on the screen
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