Chapter 1
DAQ System Overview
©
National Instruments Corporation
1-3
DAQ-STC
E Series devices use the National Instruments DAQ system timing
controller (DAQ-STC) for time-related functions. The DAQ-STC consists
of the following timing groups.
•
AI
—Two 24-bit, two 16-bit counters
•
AO
—Three 24-bit, one 16-bit counter
•
General-purpose counter/timer functions
—Two 24-bit counters
You can independently configure the groups for timing resolutions of 50 ns
or 10
µ
s. With the DAQ-STC, you can interconnect a wide variety of
internal timing signals to other internal blocks. The interconnection scheme
is flexible and completely software-configurable.
The DAQ-STC offers PFI lines to import external timing and trigger signals
or to export internally generated clocks and triggers. The DAQ-STC also
supports buffered operations, such as buffered waveform acquisition,
buffered waveform generation, and buffered period measurement. It also
supports numerous non-buffered operations, such as single pulse or pulse
train generation, digital input, and digital output.
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-DAQ determines when this is necessary and
does it automatically. If you are not using NI-DAQ, you must load these
values yourself.
You can calibrate E Series devices using either internal calibration or
external calibration.
