Frequency counters

The measurement of energy used by your home is an application to which digital metering
is well suited. It’s easier to read the drum type, digital kilowatt-hour meter than
to read the pointer type meter. When measuring frequencies of signals, digital metering
is not only more convenient, but far more accurate.
The frequency counter measures by actually counting pulses, in a manner similar
to the way the utility meter counts the number of turns of a motor. But the frequency
counter works electronically, without any moving parts. It can keep track of thousands,
millions or even billions of pulses per second, and it shows the rate on a digital display
that is as easy to read as a digital watch. It measures frequency directly by tallying up
the number of pulses in an oscillating wave, even when the number of pulses per second
is huge.
The accuracy of the frequency counter is a function of the lock-in time. Lock-in is
usually done in 0.1 second, 1 second or 10 seconds. Increasing the lock-in time by a factor
of 10 will cause the accuracy to be good by one additional digit. Modern frequency
counters are good to six, seven or eight digits; sophisticated lab devices will show frequency
to nine or ten digits.