Chapter2 HardwareOverview
NI5911 User Manual 2-8 ni.com
•The linearity of the ADC is calibrated using an internal sinewave
generator asreference.
•Thetime-to-digital converter used for RIS measurements is calibrated.
Caution Do not apply high-amplitude or high-frequency signals to the NI 5911 during
internalcalibration. For optimal calibration performance, disconnect the input signal from
the NI 5911.

Why Errors Occur During Acquisition

The NI5911 uses a heater circuit to maintain constant temperature on the
criticalcircuitry used in flexible resolution mode. If this circuit is unable to
maintain the temperature within specification,an error is generated. This
errorindicates that the temperature of the ADC is out of range and should
berecalibrated by performing an internal calibration. During acquisition in
flexibleresolution mode, an error will be gen erated if the input to the ADC
goesout of range for the converter. The fact that this condition has occurred
maynot be obvious from inspecting the data du e to the digital filtering that
takesplace on the acquired data. Therefore, an error occurs to let you know
thatt he data includes some samples that wereou tof the range of the
converter andmay 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
Thereare 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.
Youcan also call a software function to trigger the board. Figure 2-3shows
thedifferent trigger sources. When you use a digital signal, t hat signal must
beat a high TTL level for at least 40 ns before any triggers will be accepted.
Note The NI 5911 does not support delayed triggering.