A basic oscilloscope is comprised of four systems — the display, trigger, horizontal and vertical system. Each of these systems contributes to the ability of the oscilloscope to reconstruct a signal accurately. Thus, understanding each system will help users effectively use the oscilloscope in facing specific measurement challenges.
The vertical setting of an oscilloscope is one of the three significant settings that an oscilloscope user should adjust to accommodate an incoming signal. Used to vertically scale and position the waveform, the vertical controls can also be used to set the input coupling, as well as to adjust other signal conditioning. The vertical position control also enables the user to move the waveform up and down the screen.
The volts-per-division setting (written as volts/div) of the oscilloscope is a scaling factor that changes the size of the waveform displayed. If the volts/div setting is five volts and the graticule has eight main divisions, then the user can expect the whole screen to display 40 volts from top to bottom since each division of the graticule represents five volts.
It has to be emphasized that the maximum voltage that a user can display on the screen is the number of vertical divisions multiplied by the volts/div setting. The probe used to also affects the scale factor. The user must divide the volts/div scale by the probe’s attenuation factor if the oscilloscope does not do so.
Usually, the volts/div scale has either a fine gain or variable gain control for scaling a signal to a particular number of divisions. This control can be used to assist in making rise time measurements.
Coupling is the method utilized to connect an electrical signal in two or more circuits. In the oscilloscope’s case, the input coupling is the connection from the test circuit to the oscilloscope. The coupling can be set to AC (alternating current), DC (direct current) or the ground. The DC coupling setting reveals all of an input signal, while the AC coupling blocks the signal’s DC component enabling the user to view the waveform centered on zero volts. The AC coupling is also very useful when the entire signal (DC + AC) is too big for the volts/div setting.
Meanwhile, the ground setting allows oscilloscope users to view the location of the zero volts on the screen by disconnecting the input signal from the vertical system. The auto trigger mode and grounded input coupling allows users to view a horizontal line on the screen, which is the zero volts. Switching to ground from DC setting and back again provides a handy means of measuring the levels of signal voltage with respect to ground.
Many oscilloscopes feature a circuit that limits its bandwidth. Limiting the bandwidth eliminates or reduces high-frequency signal content, as well as effectively reduces the noise that often appears on the displayed waveform, enabling the oscilloscope to achieve a cleaner signal display.
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