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Chapter 3
Counters
counter sample clock. You can route an external signal or one of many different internal signals
as the sample clock. For example, you can generate a signal using one counter and route that
signal to the sample clock of another counter. Refer to Chapter 5,
Clock
Generation, for more information about which signals can be used as the source.
Counter Input Applications
The following sections list the various counter input applications available:
•
Edge Counting
•
Pulse Measurement
•
Semi-Period Measurement
•
Frequency Measurement
•
Period Measurement
•
Pulse-Width Measurement
•
Two-Edge Separation
Edge Counting
In an Edge Counting measurement task, the counter counts the number of active edges of a
signal. Figure 3-2 shows an example of edge counting.
Signal to Measure
Channel Settings
By default, the counter:
•
starts the count at 0.
•
counts edges on a default PFI terminal. Refer to Chapter 5,
Clock
Generation, for more information.
•
counts rising edges.
•
counts up always.
You can change these behaviors by configuring DAQmx Channel properties:
•
CI.CountEdges.InitialCnt—To specify the initial value of the count.
•
CI.CountEdges.Term—The signal-to-measure comes from an input terminal. To change
the signal-to-measure, specify a different terminal via this property.
3-2 | ni.com
Figure 3-2. Edge Counting
Start Task
Count
0
1
Counter Signal Routing and
2
3
Counter Signal Routing and
4
5
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