Programming instructions

Chapter 8 Controlling Your Acquisition with Triggers
© National Instruments Corporation 8-11 LabVIEW Data Acquisition Basics Manual
If you are using channel names configured in the DAQ Channel Wizard,
level
and
hysteresis
are treated as being relative to the physical units
specified for the channel. If you are not using channel names, these inputs
are treated as volts.
For more information on the conditional retrieval input cluster, look at the
AI Read VI description in Chapter 16,
Intermediate Analog Input VIs
, in
the
LabVIEW Function and VI Reference Manual
, or the LabVIEW
Online
Reference
, available by selecting
Help»Online Reference…
.
Conditional Retrieval Examples
The Acquire N Scans Analog Software Trig VI example, located in
labview\examples\daq\anlogin\anlogin.llb
, uses the
Intermediate VIs, as shown in Figure 8-9.
Figure 8-9.
Block Diagram of the Acquire N Scans Analog Software Trig VI
The main difference between this software triggering example and
hardware triggering is the use of the
conditional retrieval
input for the
AI Read VI. You set up the
trigger channel
,
trigger slope
, and
trigger
level
the same way for both triggering methods. The
pretrigger scans
value will be negated and connected to the
offset
value in the
conditional
retrieval
cluster of the AI Read VI. When the trigger conditions are met,
the VI will return the requested number of scans.