Data Display Using Oscilloscopes
Oscilloscopes
Data Display Using Oscilloscopes
Oscilloscopes
Introduction
The fundamental purpose of an oscilloscope is to measure and display voltages as a function of time. A plot of the voltages vs. time is provided in the main waveform window of the oscilloscope. The horizontal axis of the waveform window is time, and the vertical axis is voltage. The user can control the waveform display by adjusting these axes. We will provide basic ways to control these axes below.
Horizontal Axis
Figure 1 shows the basic features on the Analog Discovery™ oscilloscope relative to the horizontal (or time) axis of the oscilloscope's waveform plot. On Fig. 1, controls that are not directly related to the time axis have been “grayed out” to de-emphasize them. The primary time axis controls consist of setting the sensitivity (the scale used on the horizontal axis) and the location of the trigger point on the time axis. Primary horizontal axis controls are as follows:
- Pos: Sets the trigger point (as denoted by the black upside-down triangle at the top of the screen) relative to the center of the screen. This value can be set by typing a value in the text box, clicking and dragging the inverted black triangle indicating the trigger point, or clicking and dragging on the time axis with the left mouse button.
- Base: The time base (also called the time sensitivity or the time scale). This value sets the scale on the horizontal axis, in seconds per division. The “divisions” referred to are the major division lines, as indicated on Fig. 1. (There are minor division lines as well; these are simply present to make accurate readings easier.) The time scale can be set by typing a value in the text box, selecting a value from the drop-down menu, clicking and dragging the slider bar, or clicking and dragging on the time axis with the right mouse button.
Vertical Axis
Figure 2 shows the basic features on the Analog Discovery oscilloscope relative to control of the vertical (or voltage) axis of the oscilloscope's waveform plot. As before, controls not related directly to control of the time axis have been “grayed out” to de-emphasize them. One important thing to note about the vertical axis settings is that each channel has its own vertical scale.
Important Point
If multiple channels are displayed simultaneously, it is imperative that the user
keep in mind the fact that the vertical scales on each channel can be different.
The scale associated with the selected channel (chosen by clicking on the
tabs at the upper left of the main oscilloscope window)
is shown on the vertical axis. This scale may not be appropriate for any of the
other channels displayed!
Primary vertical axis controls are as follows for each channel. (For clarity, these controls are illustrated for only channel 1 in Fig. 2. Similar controls will appear for any other enabled channel.)
- Offset: Sets the datum point for the given channel (essentially, the channel's “zero” voltage) relative to the center of the screen. This value can be set by typing a value in the text box, selecting a value from the drop-down menu, or dragging the slider bar.
- Scale: This value sets the scale on the vertical axis, generally in volts per division. The “divisions” referred to are the major division lines, as indicated on Fig. 2. The vertical scale can be set by typing a value in the text box, selecting a value from the drop-down menu, or clicking and dragging the slider bar.
The Screenshots above are of Digilent WaveForms running on Microsoft Windows 7.
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