National Instruments Data Acquisition Device E Series - Manual (Page 132)

Chapter 10 Triggering
© National Instruments Corporation 10-3 E Series User Manual
PFI 0/AI START TRIG Pin
This pin is an analog input when configured as an analog trigger. Therefore,
it is susceptible to crosstalk from adjacent pins, resulting in false triggering
when the pin is unconnected. To avoid false triggering, ensure that this pin
is connected to a low-impedance signal source (less than 1 k
Ω source
impedance) if you plan to enable this input using the application software.
Analog Input Channel
You can select any analog input channel to drive the PGIA. The PGIA
amplifies the signal as determined by the input mode and the input polarity
and range. The output of the PGIA then drives the analog trigger detection
circuit. By using the PGIA, you can trigger on very small voltage changes
in the input signal.
When the DAQ device is waiting for an analog trigger with a AI channel as
the source, the AI muxes should not route different AI channels to the
PGIA. If a different channel is routed to the PGIA, the trigger condition on
the desired channel could be missed. The other channels could also
generate false triggers.
This behavior places some restrictions on using AI channels as trigger
sources. When you use an analog start trigger, the trigger channel must be
the first channel in the channel list. When you use an analog reference or
pause trigger, and the analog channel is the source of the trigger, there can
be only one channel in the channel list. Refer to the
Analog Trigger
Accuracy section for more information.
Analog Trigger Actions
The output of the Analog Trigger Detection circuit is the Analog
Comparison Event signal. In Traditional NI-DAQ (Legacy), this signal is
called the Analog Trigger Output Circuitry (ATCOUT). You can program
your DAQ device to perform an action in response to the Analog
Comparison Event signal. This action can affect the following:
• Analog input acquisitions
• Analog output generation
• Counter behavior
Note Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more information.