National Instruments Data Acquisition Device NI USB-621x, Руководство пользователя

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Chapter 4 Analog Input
NI USB-621x User Manual 4-4 ni.com
with this amplified voltage. The amo u nt of amplification (the gain) is
determined by the analog inp u t range, as shown in Fig u re 4-2.
Figure 4-2. NI-PGIA
Table 4-1 shows how signals are ro u ted to the NI-PGIA.
For differential meas u rements, AI 0 and AI 8 are the positive and negative
inp u ts of differential analog inp u t channel 0. For a complete list of signal
pairs that form differential inp u t channels, refer to the I/O Connector Signal
Descriptions section of Chapter 3, Connector and LED Information .
AI gro u nd-reference setting is sometimes referred to as AI terminal
config u ration.
Caution
The maxim u m inp u t voltages rating of AI signals with respect to AI GND
(and for differential signals with respect to each other) are listed in the NI USB-621x
Specifications . Exceeding the maxim u m inp u t voltage of AI signals distorts the
meas u rement res u lts. Exceeding the maxim u m inp u t voltage rating also can damage the
device and the comp u ter. NI is not liable for any damage res u lting from s u ch signal
connections.
Table 4-1. Signals Routed to the NI-PGIA
AI Ground-Reference
Settings
Signals Routed to the Positive
Input of the NI-PGIA (V
in+
)
Signals Routed to the Negative
Input of the NI-PGIA (V
in–
)
RSE AI <0..31> AI GND
NRSE AI <0..31> AI SENSE
DIFF AI <0..7> AI <8..15>
AI <16..23> AI <24..31>
V
in+
V
m
= [V
in+
– V
in–
]
×
G a in
V
m
V
in–
PGIA +
–
Me asu red
Volt a ge
In s tr u ment a tion
Amplifier