Introduction to Engineering
Camera Lab #2
What's an Oscilloscope?
An Oscilloscope is an instrument that is typically used to measure voltage as a function of time. The oscilloscope you will be using is a digital oscilloscope that has two "channels." With two channels you will be able to display the voltage at two different points in your circuit as a function of time. You will use both channels in Task 1 of this lab, but will only use one channel for Tasks 2 and 3. A picture of the front panel of the oscilloscope is shown in Figure 9. The front panel of the oscilloscope is divided into sections by function. These sections are described below.
Figure 9: Front panel of Oscilloscope
Display Screen: The largest section is the display. The results of the measurements will be plotted on a graph on the display. The horizontal axis will be time, and the vertical axis will be voltage. There are several soft keys at the bottom of the display. What they do will depend on the last button you used on other parts of the front panel. The function of these buttons at any particular time will be displayed at the bottom of the screen. In addition, the values of parameters you set with the controls (for example, the vertical scale) will be displayed on the screen (usually near the top of the screen), and the values of measurements you make can be displayed near the bottom of the graph.
Vertical: The controls marked vertical are used for controlling how the measured voltage is displayed on the screen. There are two channels, 1 and 2. The push buttons in this section are used to select the channels. The position of the zero for the vertical axis of the display can be set with the small knobs ("Position"). Separate "zeros" (reference value) can be set for each channel. The scale of the vertical axis (in Volts/division) can be set with the large knobs. Different scales can be set for each channel.
Horizontal: The controls marked horizontal are used for controlling how time is displayed on the horizontal axis of the screen. For this lab you will use the small knob to control the position of t = 0 on the screen. The large knob is used to set the scale of the horizontal axis in time units per display division.
Trigger: While the oscilloscope can be set to continuously display the voltages being measured, that will usually result in a jumble on the screen. We usually want to trigger the display at some point in time, so that the signal we want to observe gets displayed. You will use the controls in this section to define when the oscilloscope will start to display the voltages (the t = 0 point of the measurements). You will do this be setting a trigger level voltage, the trigger mode, and the trigger slope. With the trigger level you will tell the oscilloscope to define t = 0 at the point the voltage crosses some value you set with the trigger level knob. With trigger mode you tell the oscilloscope to trigger in an “AUTO,” “AUTOLEVEL,” or “NORMAL” way. We will always use “NORMAL.” With the trigger slope you tell the oscilloscope to trigger when the voltage crosses the trigger level with either a positive slope or a negative slope (and not to trigger if the voltage crosses the trigger level with the wrong slope.)
Run Control: One of the buttons in this section is the "RUN/STOP" button. You can this button to tell the oscilloscope when you are done adjusting the other controls and are ready to measure. The “single” button will be used to get only a time history trace on the display and then stop.
Measure: You will use the controls in this section to move cursors on the screen. The voltages or times corresponding to the location of the cursors will be displayed at the bottom of the graph. This will allow you to record the values of different points on the voltage vs. time graphs on the display.
Floppy Disk Drive: You will save your oscilloscope data to this disk drive by using file control buttons.