Chapter 7 Counters
NI 6124/6154 User Manual 7-14 ni.com
Table7-2 summarizes some of the differences in methods of measuring
frequency.
For information about connecting counter signals, refer to the Default
Counter/Timer Pinouts 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 either 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 channel B leads channelA 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 7-2. Frequency Measurement Method Comparison
Method
Number of
Counters
Used
Number of
Measurements
Returned
Measures High
Frequency
Signals
Accurately
Measures Low
Frequency
Signals
Accurately
1 1 1 Poor Good
1b 1 Many Fair Good
21 or 2 1Good Poor
3 2 1 Good Good