National Instruments NI 5911 Internally Calibrating the NI 5911, When Internal Calibration Is Needed, What Internal Calibration Does, Why Errors Occur During Acquisition

Chapter2 HardwareOverview
©NationalInstruments Corporation 2-7 NI5911 User Manual
Internally Calibrating the NI 5911
Internally calibrate your NI 5911 with a software function or a
LabVIEW VI. Read more about the function,
niScope_CalSelfCalibrate, in your NI-SCOPE Function Reference
Help file. LabVIEW users, see the context sensitive help (Help»Show
ContextHelp)for niscope Cal SelfCalibrate. vi.
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:
1. 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.
2. Gainand offset are calibrated for each individual input range.
3. The linearity of the ADC is calibrated using an internal sinewave
generator asreference.
4. Thetime-to-digital converter used for RIS measurements is calibrated.
Note 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 NI 5911has circuitry to detect error conditions that may affect the
acquired data.The NI 5911 uses a heater circuit to maintain constant
temperatureon the critical circuitry used in flexible resolution mode. If this
circuitis unable tomaintain the temperature within specification, an error
is generated. This error indicates that the temperature of the ADC is out