ADLINK Technology NuDAQ ACL-8454, Руководство пользователя

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Applications
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35
4.3 Pulse Width Measurement
Example : To measure pulse width (with
∆
T < 32ms)
step 1: To use fixed clock source as base time interval (or base
frequency).
step 2: Assume I nternal 2M Hz clock is used. The time base is
∆
t = 1/2M=5x10e-7 sec
The count range for measuring pulse width is:
∆
t < pulse width <
∆
t *65535 (=32.768 msec)
If the specification of the pulse width to be measured is in
the range, the 2M Hz can be used. Otherwise changing the
base frequency of the counter. The counter #3 is used in
this example.
step 3: Set jumper ‘CK3’ for internal 2 M Hz clock source.
step 4 ~ 6 : Skip these steps.
step 7: The external gate source is just the signal to be measured.
The width of the high pulse can be measured. Note that if
the pulse is shorter, the time resolution is worser. If the
pulse is wider, the limitation of the maximum pulse width
should be care.
step 8: The following block diagram illustrates the application
step 9: Write the control program. Please refer the ‘DEMO3.C’
source code.
2 M Hz
COUT3
Counter #3
8254 Chip #1
C
G
O
Jumper
CK3
Jumper
CLOCK1
Signal to be measured
Pulse Width
Polling D/I for checking the
end of a pulse
Figure 4.3 Example of pulse width measurement