National Instruments USB-621 Series User Manual page 41

Chapter 4 Analog Input
AI Ground-Reference
Settings
RSE
NRSE
DIFF
The maximum input voltages rating of AI signals with respect to AI GND
Caution
(and for differential signals with respect to each other) are listed in the NI USB-621x
Specifications. Exceeding the maximum input voltage of AI signals distorts the
measurement results. Exceeding the maximum input voltage rating also can damage the
device and the computer. NI is not liable for any damage resulting from such signal
connections.
NI USB-621x User Manual
with this amplified voltage. The amount of amplification (the gain) is
determined by the analog input range, as shown in Figure 4-2.
V
in+
V
in–
Table 4-1 shows how signals are routed to the NI-PGIA.
Table 4-1. Signals Routed to the NI-PGIA
Signals Routed to the Positive
Input of the NI-PGIA (V
AI <0..31>
AI <0..31>
AI <0..7>
AI <16..23>
For differential measurements, AI 0 and AI 8 are the positive and negative
inputs of differential analog input channel 0. For a complete list of signal
pairs that form differential input channels, refer to the
Descriptions section of Chapter 3,
AI ground-reference setting is sometimes referred to as AI terminal
configuration.
Instrumentation
Amplifier
PGIA
V = [V – V
m in+
Figure 4-2. NI-PGIA
Signals Routed to the Negative
) Input of the NI-PGIA (V
in+
Connector and LED
4-4
+
Measured
V
m
Voltage
–
] × Gain
in–
AI GND
AI SENSE
AI <8..15>
AI <24..31>
I/O Connector Signal
Information.
)
in–
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