An electronic instrument used to precisely measure the frequency of an input signal. Frequency counters are commonly used in laboratories, factories, and field environments to provide direct frequency measurements of various devices. The most common applications for frequency counters are measurement and characterization of oscillator and transmitter frequencies. See Oscillator
There are several classes of frequency counters. Basic frequency counters provide measurement of frequency only. Universal counter-timers are two-channel instruments that provide measurement of frequency, period, phase, totalize (the total number of pulses generated by some type of event over the duration of an experiment), ratio (of frequencies on two channels), and time intervals such as pulse width or rise time. Microwave counters are an extension of basic frequency counters offering coverage of microwave frequency ranges to 40 GHz and beyond.
The three main architectures are conventional counting, reciprocal counting, and continuous counting. Conventional counting is the oldest and simplest but has the lowest performance and the least measurement flexibility. A conventional counter uses a simple register to count each cycle of the input signal during a 1-s measurement gate time.
Reciprocal counting is the most common architecture. It provides improved performance and flexibility over conventional counting. The main gate is set by the user and determines the nominal time over which the measurement is to be made (measurement gate time).
Continuous counting is based on the reciprocal technique, but employs high-speed digital circuits to continuously sample the contents of the count registers. These continuous samples can be digitally processed to provide improved resolution to as many as 12 digits in 1 s of measurement time.