5-10 | ni.comChapter 5 CountersPulse versus Semi-Period MeasurementsIn hardware, pulse measurement and semi-period are the same measurement. Both measure thehigh and low times of a pulse. The functional difference between the two measurements is howthe data is returned. In a semi-period measurement, each high or low time is considered one pointof data and returned in units of seconds or ticks. In a pulse measurement, each pair of high andlow times is considered one point of data and returned as a paired sample in units of frequencyand duty cycle, high and low time or high and low ticks. When reading data, 10 points in asemi-period measurement will get an array of five high times and five low times. When you read10 points in a pulse measurement, you get an array of 10 pairs of high and low times.Also, pulse measurements support sample clock timing while semi-period measurements do not.Frequency MeasurementYou can use the counters to measure frequency in several different ways. Refer to the followingsections for information about cDAQ controller frequency measurement options:• Low Frequency with One Counter• High Frequency with Two Counters• Large Range of Frequencies with Two Counters• Sample Clocked Buffered Frequency Measurement
