Chapter 2
Hardware Overview of the NI PXI-7831R
2-4
ni.com
Connecting Analog Input Signals
The AI signals for the NI PXI-7831R are AI<0..7>+, AI<0..7>–, AIGND,
and AISENSE. The AI<0..7>+ and AI<0..7>– signals are tied to the eight
AI channels of the NI PXI-7831R. For all input modes, the AI<0..7>+
signals are connected to the positive input of the instrumentation amplifier
on each channel. The signal connected to the negative input of the
instrumentation amplifier depends on the input mode for which the
NI PXI-7831R is configured.
In differential input mode, signals connected to AI<0..7>– are routed to the
negative input of the instrumentation amplifier for each channel. In RSE
input mode, the negative input of the instrumentation amplifier for each
channel is internally connected to AIGND. In NRSE input mode, the
AISENSE signal is connected internally to the negative input of the
instrumentation amplifier for each channel. In DIFF and RSE input modes,
AISENSE is not used and can be left unconnected.
Caution
Exceeding the differential and common-mode input ranges distorts the input
signals. Exceeding the maximum input voltage rating can damage the NI PXI-7831R and
the computer. NI is
not
liable for any damage resulting from such signal connections. The
maximum input voltage ratings are listed in Table B-2,
AIGND is a common AI signal that is routed directly to the ground tie point
on the NI PXI-7831R. You can use this signal for a general analog ground
tie point to the NI PXI-7831R, if necessary.
Connection of AI signals to the NI PXI-7831R depends on the input mode
of the AI channels you are using and the type of input signal source. With
different input modes, you can use the instrumentation amplifier in
different ways. Figure 2-3 shows a diagram of the NI PXI-7831R
instrumentation amplifier.
