A demonstration of waveform positioning and scaling together with an overview of the Wave Inspector function.
Greetings once more and welcome to our 83rd Test and Measurement Video. Today’s topic is Positioning and Scaling Waveforms. This is a rather simple process because it is done merely by turning a few knobs, but it does take us into some interesting territory.
Using the Tektronix MDO3000 oscilloscope’s internal AFG or any equivalent external source, the first step is to display a waveform.
We’ll use the Ramp waveform rather than sine because the acute angles at the positive and negative peaks make it easy to see how we are positioning the waveforms relative to the scope’s Cartesian coordinates and to the time and amplitude divisions. Then you can adjust the time base and trigger point by turning the horizontal controls, which are located between the concentric Wave Inspector knobs and the number pad.
When we turn the horizontal position knob clockwise, we retard the waveform relative to its timebase along the X-axis. And when we turn it counter-clockwise, we advance the waveform, moving it closer to the left edge of the display. Of course it is important to understand that we are not doing anything to the actual electrical wave, just changing the way it is displayed.
Notice also that in performing the operation, the trigger point, represented by the small orange pointed indicator, also moves in synch with the waveform. If you press the magnifying glass button on the left in the Wave Inspector section, that perspective shows up at the top of the display in split-screen format. A pair of brackets appears in the Wave Inspector display. They enclose an exact scaled-down replica of the main time-domain display, complete with the trigger point indicator. Turning the position knob, as before the waveform in both displays moves back and forth in time while the brackets in the Wave Inspector pane remain motionless.
Wave Inspector is a valuable tool in designing, building and troubleshooting electrical systems and individual pieces of equipment, right down to the component level. Engineers and technicians have known for quite some time that these tasks can be accomplished by searching the wave records for anomalies, which can result from electromagnetic interference, impedance mismatches, cabling problems, cooling malfunction or deficient design in the area of an overworked power supply, and many other dysfunctions. Long records, greater bandwidth and higher sampling rates all make for stress in the physical layer. Exact design and installation are required if long and reliable service life is expected.
The bottom line is there is an ever increasing need for diagnostic equipment and procedures that can provide insight into the electrical environment both inside and outside the enclosure. To this end the oscilloscope, spectrum analyzer and an ever-growing arsenal of test instrumentation is required to confront current electronic challenges.
Wave Inspector plays a central role in this scenario. When oscilloscopes had much shorter record lengths, the time required to look through all the data captured in a single acquisition was not at all excessive. But as we all know, the current situation has grown problematic. As is often the case, the right tooling is the answer. Wave Inspector with its zoom capability and cinematic approach provides a window into oscilloscope memory, and its navigation and search capability simplify waveform analysis.
Going back to the horizontal controls, if we turn the scale knob clockwise, the waveform expands relative to the X-axis. We might think that the frequency has been reduced, but actually what has been changed is the time interval per division, as shown in the Channel One information bar at the bottom of the display. The number of horizontal divisions along the X-axis remains ten, the industry standard.
If Position or Scale knobs are moved after the Stop button has been pressed, re-scaling and re-positioning take place as expected, as if the Run button had been pressed afterwards.
In the Wave Inspector section, it is very interesting to press the Movie Start/Stop button. The display pans back and forth across time base. A very useful function in the Wave Inspection section is Markers, which can be created by pressing the Set/Clear button. They move with the horizontal position knob and can be saved to internal memory or external flash drive so that they can be transferred to a computer and emailed to colleagues or tech help.
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