NI USB-6008/6009 User Guide and Specifications
14
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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
section for more information about differential
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 bottom-rightmost cell of Table 6, there can be a 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.
Figure 8.
Connecting a Differential Voltage Signal
The differential input mode can measure ±20 V signals in the ±20 V range. However, the maximum
voltage on any one pin is ±10 V with respect to GND. For example, if AI 1 is +10 V and AI 5 is –10 V,
then the measurement returned from the device is +20 V.
Figure 9.
Example of a Differential 20 V Measurement
AI+
NI USB-6008/6009
AI–
Voltage
Source
–5
–10
–15
–20
20
15
10
5
0
Amplitude (V)
AI 1
AI 5
Result
