Analog Input Range - National Instruments DAQ X Series User Manual

Chapter 4 Analog Input
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Analog Input Range

Input range refers to the set of input voltages that an analog input channel
can digitize with the specified accuracy. The NI-PGIA amplifies or
attenuates the AI signal depending on the input range. You can individually
program the input range of each AI channel on your MIO X Series device.
The input range affects the resolution of the MIO X Series device for an AI
channel. Resolution refers to the voltage of one ADC code. For example, a
16-bit ADC converts analog inputs into one of 65,536 (= 2
is, one of 65,536 possible digital values. These values are spread fairly
evenly across the input range. So, for an input range of –10 V to 10 V, the
voltage of each code of a 16-bit ADC is:
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Mux—Each MIO X Series device has one analog-to-digital converter
(ADC). The multiplexers (mux) route one AI channel at a time to the
ADC through the NI-PGIA.
Ground-Reference Settings—The analog input ground-reference
settings circuitry selects between differential, referenced single-ended,
and non-referenced single-ended input modes. Each AI channel can
use a different mode.
Instrumentation Amplifier (NI-PGIA)—The NI programmable gain
instrumentation amplifier (NI-PGIA) is a measurement and instrument
class amplifier that minimizes settling times for all input ranges. The
NI-PGIA can amplify or attenuate an AI signal to ensure that you use
the maximum resolution of the ADC.
MIO X Series devices use the NI-PGIA to deliver high accuracy even
when sampling multiple channels with small input ranges at fast rates.
MIO X Series devices can sample channels in any order, and you can
individually program each channel in a sample with a different input
range.
A/D Converter—The analog-to-digital converter (ADC) digitizes the
AI signal by converting the analog voltage into a digital number.
AI FIFO—MIO X Series devices can perform both single and
multiple A/D conversions of a fixed or infinite number of samples. A
large first-in-first-out (FIFO) buffer holds data during AI acquisitions
to ensure that no data is lost. MIO X Series devices can handle multiple
A/D conversion operations with DMA or programmed I/O.
– (
10V
–
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2
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10V
305 μV
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