National Instruments USB-621 Series User Manual

Chapter 8 Counters
NI USB-621x User Manual 8-16 ni.com
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.
Figure 8-14. X1 Encoding
• X2 Encoding—The same behavior for X1 encoding holds for X2
encoding except the counter increments or 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 8-15.
Figure 8-15. X2 Encoding
Ch A
Ch B
Counter Value
7 7 6 5
5
6
Ch A
Ch B
Counter Value
56 8 97 56 8
9 7

National Instruments USB-621 Series Specifications

General

Brand	National Instruments
Model	USB-621 Series
Category	Measuring Instruments
Language	English