A frequency counter accurately measures the frequency of a repetitive electronic pulse. A signal which cycles once a second has a frequency of 1 hertz; a signal which cycles 50,000 times in 1 second has a frequency of 50 kilohertz.
A frequency counter must include a signal detector which converts the input to a series of trigger pulses. A counting circuit counts the pulses during 1 or more cycles of the instrument's clock, and a display shows the result.
The oscillator or clock signal of a frequency counter must be stable if the circuit is to make an accurate reading. Accurate instruments are often based upon crystal oscillators in carefully controlled environments.
Simple frequency counting circuitry can also be used to record the rate of physical events, such as traffic flow. The event counted must trigger an electronic sensor, creating a pulse for the input of the circuit.
Software routines can serve as frequency counters within the structure of a computer system. Measurements of the computer's CPU speed or the computer's ability to perform critical functions are the result of the frequency counter application.