NI cDAQ-9172 User Guide and Specifications 46 ni.com
Table5 summarizes some of the differences in methods of measuring
frequency.
For information on connecting counter signals, refer to the Default
Counter/Timer Routing section.
Position Measurement
You can use the counters to perform position measurements with
quadrature encoders or two-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 a single-point
(on-demand) position measurement or a buffered (sample clock) position
measurement. You must arm a counter to begin position measurements.

Measurements Using Quadrature Encoders

The counters can perform measurements of quadrature encoders that
use X1, X2, or X4 encoding. A quadrature encoder can have up to
three channels—channels A, B, and Z.

X1 Encoding

When channelA leads channel B in a quadrature cycle, the counter
increments. When channelB leads channel A in a quadrature cycle, the
counter decrements. The amount of increments and decrements per cycle
depends on the type of encoding—X1, X2, or X4.
Table 5. Frequency Measurement Method Comparison
Method
Number of
Counters Used
Number of
Measurements
Returned
Measures High
Frequency
Signals
Accurately
Measures Low
Frequency
Signals
Accurately
111Poor Good
1b 1 Many Fair Good
21 or 2 1Good Poor
321Good Good