National Instruments DAQ X Series, Руководство пользователя

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Chapter 7 Counters
X Series User Manual 7-6 ni.com
Pulse-Width Measurement
In p u lse-width meas u rements, the co u nter meas u res the width of a p u lse on
its Gate inp u t signal. Yo u can config u re the co u nter to meas u re the width
of high p u lses or low p u lses on the Gate signal.
Yo u can ro u te an internal or external periodic clock signal (with a known
period) to the So u rce inp u t of the co u nter. The co u nter co u nts the n u mber
of rising (or falling) edges on the So u rce signal while the p u lse on the Gate
signal is active.
Yo u can calc u late the p u lse width by m u ltiplying the period of the So u rce
signal by the n u mber of edges ret u rned by the co u nter.
A p u lse-width meas u rement will be acc u rate even if the co u nter is armed
while a p u lse train is in progress. If a co u nter is armed while the p u lse is in
the active state, it will wait for the next transition to the active state to begin
the meas
u rement.
Refer to the following sections for more information abo u t X Series
p u lse-width meas u rement options:
• Single Pulse-Width Measurement
• Implicit Buffered Pulse-Width Measurement
• Sample Clocked Buffered Pulse-Width Measurement
• Hardware-Timed Single Point Pulse-Width Measurement
Single Pulse-Width Measurement
With single p u lse-width meas u rement, the co u nter co u nts the n u mber of
edges on the So u rce inp u t while the Gate inp u t remains active. When the
Gate inp u t goes inactive, the co u nter stores the co u nt in the FIFO and
ignores other edges on the Gate and So u rce inp u ts. Software then reads the
stored co u nt.
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