A frequency meter is an electronic instrument that measures frequencies of light and sound waves. Frequency is defined as being the amount of times a particular sound or light waveform occurs within a given period of time, and the frequency meter counts these occurrences and their duration. A frequency meter can detect and display the frequencies of sounds and light waves below and above the detection ability of the human eyes and ears for a full spectrum of each.
The input signal a frequency meter receives usually comes from one of several kinds of input/output interfaces. These can be RS232 serial data ports, universal serial bus (USB) ports, Ethernet data link connections, or general purpose interface bus (GPIB) test equipment connections. Besides notifying of frequencies, a frequency meter can send alerts when frequencies have been exceeded. A menu interface can receive settings for what frequencies are allowable and program the frequency meter to either sound an alarm or shut down operation when frequencies are exceeded for a duration beyond a set period of time.
There is an internal oscillator, called the timebase, that provides the time signals. If the signal being received is already in electronic form, a simple interface hookup will give the reading. If the input is not electronic, a transducer in the frequency meter will need to convert the signal and perhaps amplify or filter it to then achieve an accurate read. Frequency meters, for very high frequency reads of microwave signals and beyond, require an internal prescaler to lower the frequency to a level where normal circuitry can read it.
The timebase within a frequency meter is usually a quartz crystal oscillator containing a chamber that is temperature-controlled and sealed for high accuracy measurements. Global positioning satellite (GPS) frequency receivers may also contain a timebase with a rubidium oscillator. Also, embedded systems, such as a central processing unit (CPU), can be programmed to become frequency meters of their own operations when given external frequency references for self-calibration.
Digital frequency meters are often used as test equipment or test equipment adjuncts in electronics industries. Physics and engineering endeavors related to acoustics, optics and radio waves use them as traditional measurement devices. Nuclear pulse counting from nuclear decay was among the first uses of frequency meters during World War II, and they are still in use for that purpose as radiation counters. They can also be used to reduce noise on cellphones, cameras and wireless networks, and to detect leaks in microwave ovens.