User's Manual

Chapter 2 Hardware Overview
NI 5911 User Manual 2-8 ni.com
of range and should be recalibrated by performing an internal calibration.
During acquisition in flexible resolution mode, an error will be generated
if the input to the ADC goes out of range for the converter. The fact that
this condition has occurred may not be obvious by inspecting the acquired
data due to the digital filtering that takes place on the acquired data.
Therefore, an error occurs to let you know that the data includes some
samples that were out of the range of the converter and may be inaccurate.
External Calibration
External calibration calibrates the internal reference on the NI 5911.
The NI 5911 is already calibrated when it is shipped from the factory.
Periodically, the NI 5911 will need external calibration to remain within
the specified accuracy. For more information on calibration, contact
National Instruments, or visit
ni.com/calibration
. For actual intervals
and accuracy, refer to Appendix A, Specifications.
Triggering and Arming
There are several triggering methods for the NI 5911. The trigger can be an
analog level that is compared to the input or any of several digital inputs.
You can also call a software function to trigger the board. Figure 2-3 shows
the different trigger sources. When you use a digital signal, that signal must
be at a high TTL level for at least 40 ns before any triggers will be accepted.
Note
The NI 5911 does not support delayed triggering.