412 Electrical Systems T E C H T I P Triggering Options Most digital oscilloscopes have a plethora of triggering events to choose from. Read the user’s manual for your oscilloscope and become familiar with what triggering options are available to you. Many oscilloscopes provide a button to set the trigger level to 50% of the value of the waveform. This method allows you to get into the “ball park” quickly. For most waveforms, the 50% setting works with no further adjustment of the trigger level control. More complicated waveforms may require more manipulation in order to lock the trace on the screen. Additional Oscilloscope Functions Oscilloscope controls typically include additional but- tons. Button names may vary, but the functions are similar. Always refer to the user’s manual of your spe- cifi c oscilloscope for a complete explanation of available functions. Th e following are general descriptions of the functions of common buttons: ■ Run/Stop button. Allows you to stop the sweep on the oscilloscope, “freezing” the waveform for closer examination. Th is feature is helpful when the waveform is changing too quickly to get a good look at what is happening. Th is button is not avail- able on analog oscilloscopes. ■ Single (Sweep) button. Takes a “snapshot” of the waveform. If the waveform frozen by the Run/Stop button is not useful, pressing the Single button takes another snapshot. Th is button is not available on analog oscilloscopes. ■ Autoscale button. Allows the oscilloscope to auto- matically change the voltage scale (v/div). In some instances, it is benefi cial to allow the scope to set this parameter. ■ Autoset (Auto Setup) button. Measures the incoming signal, adjusts the vertical and horizontal scales, and sets the triggering to display a wave- form. Th is option works most of the time on sim- ple waveforms. However, more complex waveforms require additional adjustment. Th is button is not a substitute for the technician becoming profi cient with oscilloscope setup and operation. ■ Save button. Stores waveforms as a fi le that can be reloaded to the oscilloscope screen or as an image that can be printed. Most digital oscilloscopes have a USB port, so you can save waveforms to a fl ash drive. ■ Display button. Allows you to set and control various aspects of the display. ■ Help button. Provides general information on how to set up a function. Th e Help button is not a sub- stitute for reading the user’s manual. ■ Measure button. Accesses a menu that allows you to set the scope to make voltage, time, frequency, pulse length, duty cycle, RMS value, and many other measurements. As many as two or three dozen measurement options may be available, depending on the model of the oscilloscope. ■ Multipurpose knob. Allows menu-specifi c adjust- ments and selections. Oscilloscopes may include buttons in addition to those described here. Always refer to the user’s manual for your specifi c oscilloscope to learn about the available functions. Cursors With regard to oscilloscopes, cursors are a pair of lines, either horizontal or vertical, whose position may be changed in order to take measurements. Examples of cursor measurements are shown in Figure 21-23. Normally, a digital oscilloscope displays the absolute position of each cursor as well as the Δ value (diff erence) between the two cursors. Portable Oscilloscopes Many digital oscilloscopes are portable (handheld) mod- els powered by batteries. See Figure 21-24. Th ey either come with a rechargeable battery included or in some cases a battery may be added as an option. Th e primary benefi t of a portable oscilloscope is the ability to use the device on the plant fl oor without being tethered to a 120 V receptacle. Th is makes the scope more versatile and allows you to measure grounded cir- cuits without the scope being connected to ground. Th is isolation is an important safety feature. Oscilloscope Inputs and Probes Oscilloscope inputs commonly have an impedance of 1 MΩ. For low frequency signals, the 1 MΩ input is Copyright Goodheart-Willcox Co., Inc.