Programming instructions

Chapter 8 Controlling Your Acquisition with Triggers
© National Instruments Corporation 8-7 LabVIEW Data Acquisition Basics Manual
Analog Triggering Examples
A common example of analog triggering in LabVIEW is the Acquire
N Scans Analog Hardware Trig VI, located in
labview\examples\
daq\anlogin\anlogin.llb
. This VI, as shown in Figure 8-6, uses the
Intermediate VIs to perform buffered acquisition, where data is stored in a
memory buffer during acquisition. After the acquisition completes, the VI
retrieves all the data from the memory buffer and displays it.
Figure 8-6.
Block Diagram of the Acquire N Scans Analog Hardware Trig VI
For more information on buffered acquisition, read Chapter 7,
Buffering
Your Way through Waveform Acquisition
.
You must tell your device the conditions on which to start acquiring data.
In LabVIEW, you can acquire data both before and after an analog trigger
signal. If the
pretrigger scans
is greater than 0, your device acquires data
before the triggering conditions and subtracts the
pretrigger scans
value
from the
number of scans to acquire
value to determine the number of
scans to collect after the triggering conditions are met. If
pretrigger scans
is 0, then the
number of scans to acquire
will be acquired after the
triggering conditions are met.
Before you start acquiring data, you must specify in the
trigger slope
input
if the acquisition is going to be triggered on the rising or falling edge of the
analog trigger signal. Aside from specifying the slope, you must enter the