Position Measurement; Measurements Using Quadrature Encoders - National Instruments Data Acquisition Device NI USB-621x User Manual

Number of
Method
1
1b
2
3

Position Measurement

© National Instruments Corporation
Table 8-2 summarizes some of the differences in methods of measuring
frequency.
Table 8-2. Frequency Measurement Method Comparison
Number of
Counters Measurements
Used Returned
1
1
1 or 2
2
For information about connecting counter signals, refer to the
Counter/Timer Pinouts
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 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 channel A leads channel B in a quadrature
cycle, the counter increments. When channel B 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.
Figure 8-14 shows a quadrature cycle and the resulting increments and
decrements for X1 encoding. When channel A leads channel B, the
increment occurs on the rising edge of channel A. When channel B
leads channel A, the decrement occurs on the falling edge of
channel A.
Measures High
Frequency
Signals
Accurately
1
Many
1
1
section.
8-15
Chapter 8
Measures Low
Frequency
Signals
Accurately
Poor
Fair
Good
Good
NI USB-621x User Manual
Counters
Good
Good
Poor
Good
Default