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Chapter 2 DAQ System Overview
NI 6124/6154 User Manual 2-4 ni.com
• Two flexible 32-bit counter/timer modules with hardware gating
• Digital waveform acquisition and generation
• Static DIO signals
• True 5 V high current drive DO
• PLL for clock synchronization
• PCI/PXI interface
• Independent scatter-gather DMA controllers for all acquisition and
generation functions
Calibration Circuitry
Calibration is the process of making adjustments to a measurement device
to reduce errors associated with measurements. Without calibration, the
measurement results of your device will drift over time and temperature.
Calibration adjusts for these changes to improve measurement accuracy
and ensure that your product meets its required specifications.
DAQ devices have high precision analog circuits that must be adjusted to
obtain optimum accuracy in your measurements. Calibration determines
what adjustments these analog circuits should make to the device
measurements. During calibration, the value of a known, high precision
measurement source is compared to the value your device acquires or
generates. The adjustment values needed to minimize the difference
between the known and measured values are stored in the EEPROM of the
device as calibration constants. Before performing a measurement, these
constants are read out of the EEPROM and are used to adjust the calibration
hardware on the device. NI-DAQmx determines when this is necessary and
does it automatically. If you are not using NI-DAQmx, you must load these
values yourself.
You can calibrate S Series devices in two ways—through internal
(or self-calibration) or through external calibration.
Internal or Self-Calibration
Self-calibration is a process to adjust the device relative to a highly accurate
and stable internal reference on the device. Self-calibration is similar to the
autocalibration or autozero found on some instruments. You should
perform a self-calibration whenever environmental conditions, such as
ambient temperature, change significantly. To perform self-calibration, use
the self-calibrate function or VI that is included with your driver software.
Self-calibration requires no external connections.