Period Measurement; Position Measurement; Measurements Using Quadrature Encoders; X1 Encoding - National Instruments cRIO-904 Series User Manual

For information about connecting counter signals, refer to the
section.

Period Measurement

In period measurements, the counter measures a period on its Gate input signal after the
counter is armed. You can configure the counter to measure the period between two rising
edges or two falling edges of the Gate input signal.
You can route an internal or external periodic clock signal (with a known period) to the Source
input of the counter. The counter counts the number of rising (or falling) edges occurring on
the Source input between the two active edges of the Gate signal.
You can calculate the period of the Gate input by multiplying the period of the Source signal
by the number of edges returned by the counter.
Period measurements return the inverse results of frequency measurements. Refer to the
Frequency Measurement

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 cRIO controller 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.
The following figure 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.
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section for more information.
Default Counter/Timer Routing