National Instruments NI 6612, Руководство пользователя

Страница: 60 / 98

3-24
|
ni.com
Chapter 3 Counters
Figure 3-25. Two-Edge Separation Measurement: Implicit Timing
To use Implicit timing, use the DAQmx Timing (Implicit) VI or function.
Sample Clock
With Sample Clock timing, on each active edge of the sample clock, the device stores one
measurement. The one measurement is the time between the most recent pair of beginning and
ending events to occur before the sample clock. Figure 3-26 shows an example of Sample Clock
timing.
Figure 3-26.
Two-Edge Separation Measurement: Sample Clock Timing
To use Sample Clock timing, use the DAQmx Timing (Sample Clock) VI or function.
Trigger Settings
By default, the counter begins measuring when software calls DAQmx Start Task. You can
change this behaviors by setting DAQmx Trigger properties.
To have the counter begin measuring in response to a hardware trigger, use an Arm Start Trigger.
1. Set ArmStart.TrigType to Digital Edge.
2. Set ArmStart.DigEdge.Src to select which signal to use as the ArmStartTrigger.
3. Set ArmStart.DigEdge.Edge to select the rising or falling edge of the signal.
Co u nter Time bas e
Co u nter V a l u e
B u ffer
Fir s t S ign a l
S econd S ign a l
1 2 3 1 2 3 1 2 3
3 3
3 3
3
3
Co u nter Time bas e
Co u nter V a l u e
B u ffer
Fir s t S ign a l
S econd S ign a l
1 2 3 1 2 3
3 3
3
Sa mple
Clock