Chapter 2
Hardware Overview
©
National Instruments Corporation
2-7
Calibration
The NI 5911 can be calibrated for high accuracy and resolution because of
an advanced calibration scheme. There are two different types of
calibration: internal, or self-calibration, and external calibration. A third
option, internal restore, restores factory settings and should be used only in
the event of a self-calibration failure.
Self-calibration is performed using a software command that compensates
for drifts caused by environmental temperature changes. You can
self-calibrate the NI 5911 without any external equipment connected.
External calibration requires you to connect an external precision voltage
reference to the device. External calibration recalibrates the device when
the specified calibration interval has expired. Refer to Appendix A,
, for the calibration interval.
Self-Calibrating the NI 5911
You can self-calibrate the NI 5911 with a software function or a
LabVIEW VI. Refer to Chapter 3,
Common Functions and Examples
, of
the
NI-SCOPE Software User Manual
, for step-by-step instructions for
self-calibrating the NI 5911.
When Self-Calibration Is Needed
To provide the maximum accuracy independent of temperature changes,
the NI 5911 contains a heater that stabilizes the temperature of the most
sensitive circuitries on the board. However, the heater can accommodate
for temperature changes over a fixed range of ±5 °C. When temperatures
exceed this range, the heater cannot stabilize the temperature, and signal
data becomes inaccurate. When the temperature range has been exceeded,
you receive a warning, and you must perform an internal calibration.
What Self-Calibration Does
Self-calibration performs the following operations:
•
The heater is set to regulate over a range of temperatures centered at
the current environmental temperature. The circuit components require
time to stabilize at the new temperature. This temperature stabilization
accounts for the majority of the calibration time. Refer to the
information.
•
Gain and offset are calibrated for each individual input range.
