National Instruments USB-6008 User Manual page 16

for grounded signal sources to eliminate this ground potential difference from the measured
signal.
Refer to Field Wiring and Noise Considerations for Analog Signals for more information. To
access this document, go to
When to Use Differential Connections with Ground-Reference Signal Sources
Use DIFF input connections for any channel that meets any of the following conditions:
• Your application requires input ranges other than ±10 V.
• The input signal is low level and requires greater accuracy.
• The leads connecting the signal to the device are greater than 3 m (10 ft).
• The input signal requires a separate ground-reference point or return signal.
• The signal leads travel through noisy environments.
• Two analog channels, AI+ and AI-, are available for the signal.
DIFF signal connections reduce noise pickup and increase common-mode noise rejection.
DIFF signal connections also allow input signals to float within the working voltage of the
device.
Refer to the Taking Differential Measurements
connections.
When to Use Referenced Single-Ended (RSE) Connections with
Ground-Referenced Signal Sources
Do not use RSE connections with ground-referenced signal sources. Use differential
connections instead.
As shown in the table in the
potential difference between GND and the ground of the sensor. In RSE mode, this ground
loop causes measurement errors.
Taking Differential Measurements
For differential signals, connect the positive lead of the signal to the AI+ terminal, and the
negative lead to the AI- terminal.
ni.com/info
Analog Input Modes and Signal Sources
Figure 8. Connecting a Differential Voltage Signal
Voltage
Source
and enter the Info Code
section for more information about differential
AI+
NI USB-6008/6009
AI–
NI USB-6008/6009 User Guide | © National Instruments | 15
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