3-31
WARNING
Exercise caution in using a stroboscope. The illusion of stopped motion is very
convincing. Do not attempt to touch the moving equipment.
Q-19.
If you are required to monitor the speed of a device with a stroboscope over an extended period
of time, what step should be taken to prolong the life of the flasher tube?
Frequency Counter Methods
Various frequency counters have found application as an ELECTRONIC TACHOMETER to obtain
accurate measurements of high-speed rotating machinery. A tachometer pickup may be used to produce
signals that are fed directly to the frequency counter. If the tachometer pickup is designed to generate 1
signal per revolution, the counter will indicate directly in revolutions per second; if the pickup is designed
to produce 60 signals per revolution, the counter will indicate directly in revolutions per minute.
AUDIO-FREQUENCY MEASUREMENTS
Audio-frequencies can be measured with a variety of nonelectronic and electronic devices.
Examples of nonelectronic measuring devices are the vibrating-reed meter and the moving-disk
frequency meter. (Both of these devices were discussed in NEETS, module 3.) They are used primarily to
measure the frequency of ac power, 60 Hz. However, such instruments do not have a wide frequency
range. The most common instruments available for the measurement of audio frequencies are
oscilloscopes and frequency counters.
OSCILLOSCOPE METHOD
The frequency of a waveform can readily be determined by using an oscilloscope. The most common
oscilloscope method of measuring a frequency is accomplished by first measuring the time duration of the
waveform. Frequency is the reciprocal of time
and may be easily computed, as shown in figure 3-24.
