Nassau Community College
Electronics and Telecommunications
Oscilloscope Voltage Measurements
(Ignoring DC Offset)
Performing Voltage Measurements:
When determining the value of a signal voltage using an oscilloscope the display (trace) on the oscilloscope must be properly set up. Then the amplitude may be determined using information from the display and vertical amplifier control settings.
The procedure outlined below allows you to accurately measure the peak to peak amplitude of a signal. Any DC voltage associated with the signal is removed. If you need to know the amplitude of the signals relative to ground do not use this procedure!!
Setting Up The Waveform Display:
- Begin by setting the vertical amplifier coupling switch ( AC GND DC ) to AC. This will block any DC on the signal eliminating DC offset.
In order to assure maximum accuracy of the measurement the trace must be made as large as possible without going off the top or bottom of the screen, as shown below. This is done by adjusting the vertical amplifier VOLTS/DIV control. Adjust the VOLTS/DIV control to yield the largest possible trace on the screen. You may have to adjust the vertical amplifier POSITION control to move the trace up or down to continue enlarging the trace.
- Use the vertical amplifier POSITION control to adjust the trace so the negative peaks are on a horizontal graticule line, as shown below.
- Use the horizontal amplifier POSITION control to adjust the trace so the positive peak is on the center graticule line, as shown below. This allows you to use the minor division marks to take an accurate measurement.
Measuring The Waveform Amplitude:
- Count the number of divisions from the negative peak to the positive peak. Remember that a minor division is 0.2 divisions (1Div / 5minor div)
- Determine the value of each division from the vertical amplifier VOLTS/DIV control setting. Be sure to look in the "window" for the type of probe being used. In most cases this is the 1X window.
- The peak to peak amplitude is VPP = # Div x V/Div