Chapter 5
Using the NI PXI-4224
5-8
ni.com
8.
Once you have added the property to the property node, right-click
the terminal to change the attributes of the property, or to add a control,
constant, or indicator.
9.
To add another property to the property node, right-click an existing
property and left-click
Add Element
. To change the new property,
left-click it and select the property you wish to define. You can also
drag the bottom of the property node down to add more channels to the
node.
Note
Refer to the
LabVIEW Help
for information about property nodes and specific
NI-DAQmx properties.
Synchronization and Triggering
If you have multiple NI PXI-4224 devices, you can synchronize them to
acquire samples at the same time and at the same rate. You can use multiple
NI PXI-4224 devices to acquire and analyze complex signals.
For multiple NI PXI-4224 devices to start an acquisition simultaneously,
they all must reference a common start trigger. To prevent drift over the
course of the acquisition, they must share a common timebase or sample
clock.
The NI PXI-4224 that generates the start trigger and the timebase for all of
the synchronized devices is called the
master
. The master NI PXI-4224
exports the shared timing signals through the PXI bus to the slave devices.
Each NI PXI-4224 contains a DAQ-STC chip that is capable of generating
a hardware sample clock based on its timebase clock and start trigger. This
causes the slave device to acquire samples at the same time as the master.
The preferred method of synchronization is to use a shared timebase, but it
is also possible to synchronize multiple NI PXI-4224 devices by sharing
the sample clock between them. This manual only discusses the shared
timebase method.
Synchronizing the NI PXI-4224
Figure 5-2 shows a typical program flowchart for synchronizing the sample
clocks and start triggers of two devices, taking a measurement, and clearing
the data.
