National Instruments BNC-208 Series, Руководство пользователя

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Chapter 2 BNC-2080 Board
© National Instruments Corporation 2-13 BNC-208X Series User Manual
As described in Chapter 2 of your MIO-16 board user manual, the input configuration of the
MIO-16 depends on the type of signal source. There are two types of signal sources:
nonreferenced or floating signals and ground-referenced signals. To measure floating signal
sources, the MIO-16 should be configured for the RSE mode or DIFF mode with bias resistors.
To measure ground-referenced signal sources, the MIO-16 should be configured for the NRSE
mode or DIFF mode. Both types of signal sources and the recommended methods for MIO-16
board connection are discussed as follows.
Connecting Nonreferenced (or Floating) Signal Sources
A floating signal source is a signal source that is not connected in any way to the building ground
system, but has an isolated ground-reference point. If an instrument or device has an isolated
output, that instrument or device falls into the floating signal source category. Some examples of
floating signal sources are outputs for: thermocouples, transformers, battery-powered devices,
optical isolators, and isolation amplifiers. The ground reference of a floating source must be tied to
the ground of the data acquisition board to establish a local or onboard reference for the signal.
Differential Inputs
To provide a return path for the instrumentation amplifier bias currents, floating sources must have
a 10-k
1
to 100-k
1
resistor to AIGND on one input if DC-coupled, or both inputs if AC-coupled.
For more detailed information on connections to floating signal sources and differential inputs,
refer to the configuration
chapter in your MIO-16 board user manual. These bias resistors can be
installed in positions
B
and
D
(Table 2-2 and Figure 2-3) of the BNC-2080 board. Figure 2-11
shows both the schematic and the component placement for a single 100-k
1
bias return resistor on
the negative input from a floating source connected to Channel 1 (the
D
position in Table 2-2).
Additional signal conditioning circuitry, such as filters and attenuators, as described in the sections
Building Lowpass Filters , Building Highpass Filters ,
and
Building Attenuators
(
Voltage Dividers
)
later in this chapter, can be built in the open component positions.