User Guide

Chapter 2 Hardware Overview
NI 5911 User Manual 2-8 ni.com
• The linearity of the ADC is calibrated using an internal sinewave
generator as reference.
• The time-to-digital converter used for RIS measurements is calibrated.
Caution
Do not apply high-amplitude or high-frequency signals to the NI 5911 during
internal calibration. For optimal calibration performance, disconnect the input signal from
the NI 5911.
Why Errors Occur During Acquisition
The NI 5911 uses a heater circuit to maintain constant temperature on the
critical circuitry used in flexible resolution mode. If this circuit is unable to
maintain the temperature within specification, an error is generated. This
error indicates that the temperature of the ADC is out 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 from inspecting the 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 NI, 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.