3-32
Figure 3-24.—Oscilloscope method of determining frequency.
Another common method of determining the frequency of a waveform is by using Lissajous patterns.
This method was discussed in NEETS, module 19.
FREQUENCY COUNTER METHOD
While oscilloscopes can be used to compare rectangular waveforms for the purpose of measuring the
frequency of a signal, frequency counters, as shown in figure 3-25, are much more useful for this purpose.
The fundamental measurement of frequency is accomplished by totaling the number of cycles into the
counter for a precise period of time. The result is then displayed as an exact digital readout. The audio-
frequency signal must be of sufficient amplitude to trigger the counter. The AUTO-MANUAL switch
provides two methods of frequency counter operation. One method is to initiate the count simultaneously
with the initiation of the signal to be measured. With this method, the AUTO-MANUAL switch should be
set to the MANUAL position. The second method assumes that the signal to be measured has been
operating over some indefinite period of time and that it will continue to do so after a measurement has
been taken (hence, only that segment of the signal required to make the frequency measurement is
important). With this method, the AUTO-MANUAL switch is to be set to the AUTO position.
