Measurements Using Quadrature Encoders - National Instruments M Series User Manual

Refer to the following sections for more information about the M Series position measurement
options:

Measurements Using Quadrature Encoders

•
Measurements Using Two Pulse Encoders
•
Buffered (Sample Clock) Position Measurement
•
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 7-14 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.
Ch A
Ch B
Counter Value
X2 Encoding—The same behavior 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 7-15.
Ch A
Ch B
Counter Value 5
X4 Encoding—Similarly, the counter increments or decrements on each edge of
•
channels A and B for X4 encoding. Whether the counter increments or decrements depends
on which channel leads the other. Each cycle results in four increments or decrements, as
shown in Figure 7-16.
Ch A
Ch B
Counter Value 5 6 7
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
Figure 7-14. X1 Encoding
6 7 7
5
Figure 7-15. X2 Encoding
6 7 8 9 9
Figure 7-16. X4 Encoding
8 9 10 11 12 13 13 12
M Series User Manual
6 5
8 7 6 5
11 10 9 8 7 6 5
© National Instruments | 7-15