18 | ni.com | NI USB-6001/6002/6003 User Guide
Multichannel Scanning Considerations
The NI DAQ device can scan multiple channels at high rates and digitize the signals accurately.
However, you should consider several issues when designing your measurement system to
ensure the high accuracy of your measurements.
• Use Low Impedance Sources—To ensure fast settling times, your signal sources should
have an impedance of <1 k. Large source impedances increase the settling time of the
NI DAQ device and decrease the accuracy at fast scanning rates. For more information
about decreasing the source impedance of an analog signal, go to
ni.com/info and enter
the Info Code rdbbis.
• Use Short High-Quality Cabling—Using short high-quality cables can minimize several
effects that degrade accuracy including crosstalk, transmission line effects, and noise. The
capacitance of the cable also can increase the settling time.
• Avoid Scanning Faster Than Necessary—Design your system to scan at slower speeds
to give the NI DAQ device more time to settle to a more accurate level when switching
between channels.
AI Start Trigger
You can configure PFI 0 or PFI 1 as the AI Start Trigger for analog input tasks. Refer to the
Using PFI to Trigger an Analog Input Acquisition section for more information.
Analog Output
Figure 11 shows the analog output circuitry of the NI USB-6001/6002/6003.
Figure 11. Analog Output Circuitry
AO Data
AO Sampling ClockAO Start Trigger
AO FIFO
B
uffer
DAC 0
Protection
B
uffer
DAC 1
Protection
AO 1
AO GND
AO 0
16-Position
Screw Terminal
Pl
ug
I/O Connector
DAC
Control
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