Position Measurement; Measurements Using Quadrature Encoders - National Instruments NI cDAQ-9181 User Manual

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.
Refer to the following sections for more information about the cDAQ chassis 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 5-17 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.
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 5-18.
Counter Value 5
Figure 5-17. X1 Encoding
Ch A
Ch B
5 6
Figure 5-18. X2 Encoding
Ch A
Ch B
6 7
NI cDAQ-9181/9184/9188/9191 User Manual
7 7
8 9 9 8
6 5
7 6 5
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