Chapter 7 CountersNI 6232/6233 User Manual 7-16 ni.comFor information on connecting counter signals, refer to the Default CounterTerminals section.Position MeasurementYou can use the counters to perform position measurements withquadrature encoders or two-pulse encoders. You can measure angularposition with X1, X2, and X4 angular encoders. Linear position can bemeasured with two-pulse encoders. You can choose to do either a singlepoint (on-demand) position measurement or a buffered (sample clock)position measurement. You must arm a counter to begin positionmeasurements.Measurements Using Quadrature EncodersThe counters can perform measurements of quadrature encoders that useX1, X2, or X4 encoding.A quadrature encoder can have up to three channels—channels A, B, and Z.X1 EncodingWhen channel A leads channel B in a quadrature cycle, the counterincrements. When channel B leads channel A in a quadrature cycle, thecounter decrements. The amount of increments and decrements per cycledepends on the type of encoding—X1, X2, or X4.Figure 7-15 shows a quadrature cycle and the resulting increments anddecrements for X1 encoding. When channel A leads channel B, theincrement occurs on the rising edge of channel A. When channel B leadschannel A, the decrement occurs on the falling edge of channel A.Table 7-2. Frequency Measurement Method ComparisonMethodNumber ofCounters UsedNumber ofMeasurementsReturnedMeasures HighFrequencySignalsAccuratelyMeasures LowFrequencySignalsAccurately1 1 1 Poor Good1b 1 Many Fair Good2 1 or 2 1 Good Poor3 2 1 Good Good
