©
National Instruments Corporation
11
NI USB-6008/6009 User Guide and Specifications
Analog Input
The NI USB-6008/6009 has eight analog input channels that you can use for four differential analog
input measurements or eight single-ended analog input measurements.
Figure 7 shows the analog input circuitry of the NI USB-6008/6009.
Figure 7.
NI USB-6008/6009 Analog Input Circuitry
The main blocks featured in the NI USB-6008/6009 analog input circuitry are as follows:
•
MUX
—The NI USB-6008/6009 has one analog-to-digital converter (ADC). The multiplexer
(MUX) routes one AI channel at a time to the PGA.
•
PGA
—The progammable-gain amplifier provides input gains of 1, 2, 4, 5, 8, 10, 16, or 20 when
configured for differential measurements and gain of 1 when configured for single-ended
measurements. The PGA gain is automatically calculated based on the voltage range selected in the
measurement application.
•
ADC
—The analog-to-digital converter (ADC) digitizes the AI signal by converting the analog
voltage into digital code.
•
AI FIFO
—The NI USB-6008/6009 can perform both single and multiple analog-to-digital
conversions of a fixed or infinite number of samples. A first-in-first-out (FIFO) buffer holds data
during AI acquisitions to ensure that no data is lost.
Analog Input Modes and Signal Sources
You can configure the AI channels on the NI USB-6008/6009 to take differential or referenced
single-ended (RSE) measurements. Table 6 summarizes the recommended analog input mode(s) for
floating signal sources and ground-referenced signal sources. Refer to Table 5 for more information
about I/O connections for single-ended or differential measurements.
AI
+2.5 V
REF
39.2 k
Ω
127 k
Ω
30.9 k
Ω
PGA
Input Range
Selection
AI FIFO
ADC
MUX
