Position Measurement; Measurements Using Quadrature Encoders - National Instruments NI 6221 User Manual

Chapter 7 Counters
Number of
Method
1
1b
2
3

Position Measurement

M Series User Manual
for your application. Another disadvantage of Method 2 is that it
requires two counters (if you cannot provide an external signal of
known width). An advantage of Method 2 is that the measurement
completes in a known amount of time.
• Method 3 measures high and low frequency signals accurately.
However, it requires two counters.
Table 7-2 summarizes some of the differences in methods of measuring
frequency.
Table 7-2. Frequency Measurement Method Comparison
Number of
Counters Measurements
Used
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 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.

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.
Measures High
Returned
1
Many
1
1
section.
7-14
Measures Low
Frequency Frequency
Signals
Accurately Accurately
Poor
Fair
Good
Good
Signals
Good
Good
Poor
Good
Default
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