National Instruments NI 6612, Руководство пользователя

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Chapter 3 Counters
• To specify on which edge, rising or falling, to begin the measurement, select the appropriate
property from the following list that corresponds to the type of channel created, and then
set this property to
rising or falling .
– CI.Pulse.Freq.StartingEdge
– CI.Pulse.Time.StartingEdge
– CI.Pulse.Ticks.StartingEdge
Timing Settings
The timing settings determine when the device measures the signal.
On-Demand
By default, the counter uses On-Demand (no sample clock) timing. Figure 3-8 shows an
example of On-Demand timing. The following sequence of events describes On-Demand
timing:
1. Software calls DAQmx Start Task.
2. The device measures the first full pulse on the signal-to-measure.
3. The device waits until you call DAQmx Read. The device ignores the signal-to-measure
while waiting.
4. The device returns the measurement.
5. The device then measures the next full pulse on the signal-to-measure.
6. Steps 3, 4, and 5 are repeated.
Implicit
With Implicit timing, the device measures the high and low time of every pulse on the
signal-to-measure. The measurements are stored in a buffer. Each call to DAQmx Read returns
values from this buffer. Figure 3-9 shows an example using Implicit timing.
Figure 3-9.
Pulse Measurement: Implicit Timing
To use Implicit timing, use the DAQmx Timing (Implicit) VI or function.
DAQmx
S t a rt T as k
S ign a l to
Me au re
Co u nter
Time bas e
H L
4 2
H L
4 2
4 4
6 2
2 2
H L
4 2
4 4
6 2
H L
4 2
4 4
B u ffer