National Instruments cDAQ-9172 User Manual download pdf (Page 54)

NI cDAQ-9172 User Guide and Specifications 54 ni.com

Table 6 summarizes some of the differences in methods of measuring

frequency.

For information on connecting counter signals, refer to the Default

Counter/Timer Routing section.

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 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.

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.

Table 6. Frequency Measurement Method Comparison

Method

Number of

Counters Used

Number of

Measurements

Returned

Measures High

Frequency

Signals

Accurately

Measures Low

Frequency

Signals

Accurately

1 1 1 Poor Good

1b 1 Many Fair Good

2 1 or 2 1 Good Poor

3 2 1 Good Good

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 83 84

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National Instruments cDAQ-9172 User Manual Page 54