Combine graphsA new graph can be added into instrument session that include two or more graphs. That feature could be interesting when graph comparison is needed or you want to perform math operation that require more then one signal (see below). To start adding a new graph, select
Add chart option in the upper right corner:
A new message for graph selection is displayed:
All graphs that belongs to instrument session history will be displayed with check box for selection. We'll select two graphs in our example:
Confirm with blue button
Add chart and new item that combine selected graph will be added at the end of the instrument session history:
Graph measurements (math operations)If session item type is graph directly acquired from instrument, or imported as file it is possible now to perform a first batch of math operations on it. Please note that this is a still under development, we are still missing a lots of important operations and performance and capability of currently supported is a subject for further improvements. To enter graph, you have to click on when cursor shape is changed to "preview" (not select it, we have currently an issue with that which is reported as
#57 in GitHub!). We'll use newly created graph just mentioned above and get the following:
Here we can see a new added selection
Add measurement in
Measurements tab. Please note that you can select and move any of the available tabs and rearrange them to serve you better.
For example we can add A - B measurement (note that Y-axis resolution can be changed just in one direction, that is reported as
#55):
FFT is also added, but has performance issue, and we'll try to use some library written in C/C++ to improve calculation speed. Its performance is also heavily dependent of number of used samples. Currently we are working will all samples within selected area. We have to find a way how to use selected samples from complete stream without significantly affect resulting spectrum appearance.
Other issue is related to selected duration. We can see that on 1 kHz sinewave generated with Rigol signal generator (set to 5 Vpp, 0 V offset). If the sampling rate is huge (1 GSPS) and selecting only about one period FFT (rectangle) spectrum looks like this (also note that more then one measurement type can be visible simultaneously):
Calculated frequency is pretty accurate: 1.012 KHz. But, if we select on the same graph more then a single period, we'll get the following:
Calculated frequency is now 1.318 KHz. More predictable results can be expected if more periods are included into selection that presume also lower sampling rate. The same sinewave measured on the same instrument with 125 MSPS will looks like this:
A word about graph navigation. When graph is opened for the first time its displayed as
Zoom default option is selected:
Zoom all option will try to display it as big as possible, in our case amplitude (y-axis) resolution will be changed:
You can select with a cursor part of the graph to zoom into it (displayed it as big as possible on x-axis). Simply click on the first point, drag and release to the second point. Here is how that could looks like before releasing the mouse button:
It's possible to enable or disable X-axis and Y-axis rulers (see
Rulers tab). In that case cursor selection define part of the graph that will be used for measurements. In that case selection boundaries will looks a little bit different (bold white lines):
Click inside selection to move it inside graph, or select boundary line to resize it.
Finally note about graph export: you can save it as file using
Save option beneath graph (visible when you exit preview mode in instrument session history). In that case graph will be saved in raw format an in our case it will generate a 7.5 MB file size. But if you'd like to exchange graph with other EEZ Studio users, use
Export as notebook file option described in previous post. In that case the same file will be compressed and only 18.6 KB in size.
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