6 - Frequency, time and event counters

Abstract

This chapter illustrates frequency, time, and event counters. Frequency, time and event measurements are accomplished with the use of test instruments with the generic name counters, sometimes called universal counter timers (VCTs). In frequency and time measurements the primary cause of measurement error is the accuracy with which the time base maintains its frequency of oscillation. Counters are generally digital in operation and so have a digital read-out display of LED, LCD, and vacuum fluorescent or similar form. Operation of all counters depends on the principle of gating signal over a time, while counting the number of pulses of the signal during that time. Direct gated counters are very accurate within the limitations of the method. In direct gated counters the gating period is normally achieved by dividing down the output signal of a stable high frequency reference oscillator, sometimes called the time base or clock. On the other hand, in frequency measurements, the counter gate is controlled automatically by the internal time base.