Two high-end test instruments are connected to display waveforms and Lissajous patterns.
Hi and welcome to our 56th Test and Measurement video. Today we’ll do one of my favorite things in the world of electronics, and that is to connect two products by different manufacturers and see them work in concert. Both very high quality instruments.
Siglent’s SDG2122X arbitrary waveform generator and the Tektronix MDO3104 oscilloscope are mirror images of one another in the sense that the Siglent waveform generator synthesizes and outputs internal or user-created waveforms while the Tektronix inputs and displays these signals. It also contains an internal arbitrary function generator, which we will be using today in conjunction with a waveform from the Siglent instrument. Both of these hookups use simple BNC cables, which are supplied along with the machines or can be obtained locally.
The Siglent arbitrary waveform generator has two outputs, one of which is connected via BNC cable to the Tektronix oscilloscope’s analog channel one input.
For the second signal, we have used the same type of cable to go from the arbitrary function generator port on the back panel of the oscilloscope to the analog channel two input on the front panel.
The Siglent arbitrary waveform generator has output switches for the two channels, so we need to make sure that the correct output is toggled on. Similarly, in the oscilloscope the channel one switch has to be turned on. Depending on what was last done in the oscilloscope, we may need to press Autoset to get a coherent display.
And there it is – a waveform created in the Siglent arbitrary waveform generator and conveyed to the Tektronix oscilloscope. Pressing waveform in the Siglent, we see the library of six internally generated waveforms plus the point of departure for user-defined arbitrary waveforms. We’ll go back to sine and bring up the sine wave that is internally generated in the Tektronix oscilloscope. Finally, we need to adjust the frequency of the Tektronix sine wave, so that the two are the same. To do this, press AFG in the oscilloscope, then the Waveform Settings soft key. In the Siglent instrument, the frequency is 1 MHz. To make the frequency of the Tektronix sine wave the same, you can use Multipurpose Knob a to run it up from 100 KHz, but it is always easier to use the keypad. Since the frequency is currently highlighted, just press 1 followed by Units, which is MHz. Now the frequencies of the two waveforms are in agreement. Press Autoset and Menu Off to get a good display. Notice that there is a frequency drift causing a slowly changing phase angle of the Tektronix sine wave with respect to the Siglent sine wave. This is very slight when you consider that the two waveforms are oscillating a million times per second.
Now it’s going to get even more interesting.
Press Acquire, and in the menu that comes up below the display, press the soft key associated with XY Display. In the submenu to the right of the display, select Triggered XY. In the small display at the left is the Lissajous pattern for two sine waves. If you want to see exactly what is happening, toggle YT On. Now the conventional two-channel time domain display and the XY display are shown in split-screen format. This makes clear some aspects of a Lissajous pattern.
You can see that when the two waveforms become exactly in phase, the Lissajous pattern is comprised of a straight diagonal line that begins at the upper right corner and descends to the lower left corner. When the two sine waves are 180 degrees out of phase, the Lissajous pattern is a straight diagonal line that begins at the upper left corner and descends to the lower right corner. When the two signals are 90 degrees and 270 degrees out of phase, the Lissajous pattern are perfect circles that subsequently decompose into the straight diagonal lines.
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