AC1 Fundamentals Unit 2 – AC Measurements
Exercise 1 – AC Amplitude Measurement
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to measure the amplitude of ac
waveforms by using an oscilloscope. You will verify your results with a multimeter.
DISCUSSION
- The number of voltage or current units between the maximum point (positive peak) of the ac
waveform and the minimum point (negative peak) of the ac waveform is referred to as the
peak-to-peak value. - The subscript pk-pk is used to designate peak-to-peak amplitude measurements.
- An amplitude measurement from the horizontal axis to either the positive peak or the
negative peak is designated as the peak value. - The subscript pk is used to designate these amplitude values.
- The peak value of a waveform is one half the peak-to-peak measurement.
- Oscilloscopes are used to measure the peak or peak-to-peak amplitude of an ac signal. The
amplitude scale should be expanded to display the largest possible signal. This provides the
ability to make a more accurate measurement. - A measured value indicating that an ac signal has the same heating power as an equivalent dc
value is called the effective or rms (root mean square) value. - Subscripts (Vac, Vrms, or Veff) are used to designate specific amplitude measurements.
- The product of the peak amplitude of a sine wave and 0.707 gives the rms value (Vrms = Vpk
X 0.707). - When using the ac function of a general-purpose digital or analog multimeters, the reading is
in rms. If the multimeter is analog, it may also have a “peak ac” scale. Many modern
multimeters are usable to 100 kHz and above. - The average value (indicated by a subscript of avg) of the amplitude of the ac waveform is
calculated using this equation: Vavg = 0.637 X Vpk