National Instruments NI 6238 - Manual (Page 21)

Chapter 2 DAQ System Overview
© National Instruments Corporation 2-3 NI 6238/6239 User Manual
Calibration Circuitry
The M Series analog inputs and outputs can self calibrate to correct gain
and offset errors. You can calibrate the device to minimize AI and AO
errors caused by time and temperature drift at run time. No external
circuitry is necessary; an internal reference ensures high accuracy and
stability over time and temperature changes.
Factory-calibration constants are permanently stored in an onboard
EEPROM and cannot be modified. When you self-calibrate the device,
software stores new constants in a user-modifiable section of the EEPROM.
To return a device to its initial factory calibration settings, software can
copy the factory-calibration constants to the user-modifiable section of the
EEPROM. Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more
information on using calibration constants.
Sensors and Transducers
Sensors can generate electrical signals to measure physical phenomena,
such as temperature, force, sound, or light. Some commonly used sensors
are strain gauges, thermocouples, thermistors, angular encoders, linear
encoders, and resistance temperature detectors (RTDs).
Note Current input measurement devices can only interface with sensors that output a
current.
To measure signals from these various transducers, you must convert them
into a form that a DAQ device can accept. For example, the output voltage
of most thermocouples is very small and susceptible to noise. Therefore,
you may need to amplify or filter the thermocouple output before digitizing
it, or use the smallest measurement range available within the DAQ device.
For more information about sensors, refer to the following:
• For general information about sensors, visit ni.com/sensors .
• If you are using LabVIEW, refer to the LabVIEW Help by selecting
Help»Search the LabVIEW Help in LabVIEW, and then navigate to
the Taking Measurements book on the Contents tab.
• If you are using other application software, refer to Common Sensors
in the NI-DAQmx Help, which can be accessed from Start»All
Programs»National Instruments»NI-DAQ»NI-DAQmx Help.