7-8 | ni.comChapter 7 CountersNote that if you are using an external signal as the Source, at least one Source pulse should occurbetween each active edge of the Gate signal. This condition ensures that correct values arereturned by the counter. If this condition is not met, consider using duplicate count prevention,described in the Duplicate Count Prevention section.For information about connecting counter signals, refer to the Default Counter/Timer Pinoutssection.Frequency MeasurementYou can use the counters to measure frequency in several different ways. You can choose oneof the following methods depending on your application:• Low Frequency with One Counter• Low Frequency with One Counter (Averaged)• High Frequency with Two Counters• Large Range of Frequencies with Two CountersRefer to the Choosing a Method for Measuring Frequency section for a detailed comparison ofthese frequency measurement methods.Low Frequency with One CounterIn this method, you measure one period of your signal using a known timebase. This method isgood for low frequency signals.You can route the signal to measure (F1) to the Gate of a counter. You can route a knowntimebase (Ft) to the Source of the counter. The known timebase can be 80MHzTimebase. Forsignals that might be slower than 0.02 Hz, use a slower known timebase.You can configure the counter to measure one period of the gate signal. The frequency of F1 isthe inverse of the period. Figure 7-10 illustrates this method.Figure 7-10. Low Frequency with One CounterF1FtF1FtGateSource1 2 3 … NSingle PeriodMeasurement…Period of F1 = NFtFrequency of F1 = NFtInterval MeasuredArtisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
