Elenco 30MHz Dual Trace - Manual (Page 55)

52
APPLICATION
Method No.2
(Refer to Fig.11)
While the previously described method relies upon direct period measurement of
one cycle, the frequency may also be measured by counting the number of cycles
present in a given time period.
1. Set the oscilloscope to display several cycles of the waveform. The VAR SWEEP
control must be set to CAL.
2. Count the number of cycles of waveform between a chosen set of vertical
graduation lines.
3. Multiply the number of horizontal divisions by the sweep TIME/DIV setting to
calculate the time sweep TIME/DIV setting to calculate the time span. Multiply the
reciprocal of this value by the number of cycles present in the time span. If X10
magnification is used, multiply this further by 10. Note that errors will occur for
displays having only a few cycles.
The measurement is summarized by the following equations:
Freq =
For the example shown in Fig.16, there are 10 cycles within 7 divisions. If the
sweep TIME/DIV is 5 μ s and X10 magnification is not used, the frequency is
calculated as follows:
Freq = = 285.7 kHz
100
90
10
0
Fig.10 Alternate Method Of Frequency Measurement
Count cycles between this portion
No of cycles ( x10 for x 10)
Hor div x TIM/DIV
10 (cycles)
7 (div) x 5 ( s) μ