Frequency

=== Frequency counter ===
{{main|Frequency counter}}
[[File:Frequency counter.jpg|thumb|left|Modern frequency counter]]

Higher frequencies are usually measured with a [[frequency counter]]. This is an [[electronic instrumentation|electronic instrument]] which measures the frequency of an applied repetitive electronic [[signal (electronics)|signal]] and displays the result in hertz on a [[digital display]]. It uses [[digital logic]] to count the number of cycles during a time interval established by a precision [[quartz clock|quartz]] time base. Cyclic processes that are not electrical, such as the rotation rate of a shaft, mechanical vibrations, or [[sound wave]]s, can be converted to a repetitive electronic signal by [[transducer]]s and the signal applied to a frequency counter. As of 2018, frequency counters can cover the range up to about 100&nbsp;GHz. This represents the limit of direct counting methods; frequencies above this must be measured by indirect methods.