Chapter2 HardwareOverview
©NationalInstruments Corporation 2-7 NI5911 User Manual
Calibration
The NI 5911 can be calibrated for very high accuracy and resolution due
to an advanced calibration scheme. There are two different types of
calibration:internal, o r self, calibration and external calibration. A third
option,internal restore, restores factory settings and should be used only in
the eventof a self-calibration failure.
Internal calibration is performed via a software command that
compensatesfor drifts caused by environmental temperature changes. You
can internally calibrate your NI 5911 without any external equipment
connected.External calibratio n recalibrates the devicewhen the specified
calibration interval has expired. See Appendix A, Specifications,forthe
calibrationinterval. External calibration requires you to connect an external
precision voltagereference to the device.

Internally Calibrating the NI 5911

Internally calibrate your NI 5911 with a software function or a
LabVIEW VI. See Chapter 3, Common Functions and Examples,ofyour
NI-SCOPE Software User Manual for step-by-step instructions for
calibrating your digitizer.

When Internal Calibration Is Needed

To provide themaximum accuracy independent of temperature changes,
the NI5 911 containsa heater that stabilizes the temperature of the most
sensitive circuitries on the board. However, the heater can accommodate
fortemperature changes over a fixed range of ±5 °C.W hen temperatures
exceedthis range, the heater no longer is able to stabilize the temperature,
andsignal data becomes inaccurate. When the temperature range has been
exceeded,you receive a warning, and you need to perform an internal
calibration.

What Internal Calibration Does

Internalcalibration performs the following operations:
•The heater is set to regulateover a range of temperatures centered at
thecurrent environmental temperature. The circuit components require
acer tain amount of time to stabilize at the new temperature. This
temperaturestabilization accounts for the majority of the calibration
time.
•Gainand offset are calibrated for each individual input range.