© National Instruments | 5-19NI cDAQ-9181/9184/9188/9191 User ManualPosition MeasurementYou can use the counters to perform position measurements with quadrature encoders ortwo-pulse encoders. You can measure angular position with X1, X2, and X4 angular encoders.Linear position can be measured 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 position measurements.Refer to the following sections for more information about the cDAQ chassis positionmeasurement options:• Measurements Using Quadrature Encoders• Measurements Using Two Pulse Encoders• Buffered (Sample Clock) Position MeasurementMeasurements Using Quadrature EncodersThe counters can perform measurements of quadrature encoders that use X1, X2, or X4encoding. A quadrature encoder can have up to three channels—channels A, B, and Z.• X1 Encoding—When channel A leads channel B in a quadrature cycle, the counterincrements. When channel B leads channel A in a quadrature cycle, the counterdecrements. The amount of increments and decrements per cycle depends on the type ofencoding—X1, X2, or X4.Figure 5-17 shows a quadrature cycle and the resulting increments and decrements for X1encoding. When channel A leads channel B, the increment occurs on the rising edge ofchannel A. When channel B leads channel A, the decrement occurs on the falling edge ofchannel A.Figure 5-17. X1 Encoding• X2 Encoding—The same behavior holds for X2 encoding except the counter incrementsor decrements on each edge of channel A, depending on which channel leads the other.Each cycle results in two increments or decrements, as shown in Figure 5-18.Figure 5-18. X2 EncodingCh ACh BCounter Value 7 7 6 55 6Ch ACh BCounter Value 5 6 8 97 56 89 7
