© National Instruments
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7-15
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.
Figure 7-14.
X1 Encoding
•
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.
Figure 7-15.
X2 Encoding
•
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.
Figure 7-16.
X4 Encoding
Ch A
Ch B
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