BNC-2081 Board
Chapter 3
BNC-208X Series User Manual
3-8
© National Instruments Corporation
Mounting
The BNC-2081 board is equipped with metal standoffs so the board can be placed on a workbench near
the host computer. You can use an optional rack-mount chassis, which can be fitted with a flat, acrylic
plastic cover. When the BNC-2081 board is mounted in the chassis, the board can be grounded to its
metal standoffs, and therefore to the rack. For more information, see Chapter 4,
Application Notes
The open component positions on the BNC-2081 board make adding signal conditioning components to
the analog input signals easier. Several applications are covered in this section, including filtering and
attenuation.
The figures in this section give examples on a specific input channel. If you want to install the circuit on
a different channel, consult Table 3-1 to determine the equivalent component positions for the other
channels.
Soldering and Desoldering on the BNC-2081 Board
With the applications discussed here, you must make modifications to the printed circuit board, usually
by removing jumpers and adding components. The BNC-2081 board is shipped with one jumper in the
C
position (see Table 3-1 and Figure 3-3). Use a low-wattage soldering iron (20 to 30 W) when
soldering to the board. To desolder on the BNC-2081, vacuum-type tools work best. Use care when
desoldering to avoid damaging component pads. Only rosin-core, electronic-grade solder should be
used. Acid-core solder damages the printed circuit board and components.
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.
No special components are needed to measure signals from floating sources connected to the
BNC-2081 board. Because the negative side of the single-ended inputs is grounded, all floating sources
are referenced to the same ground. The inputs of the BNC-2081 board can be left in the factory-original
condition, that is, with a jumper in the series position,
C
(see Table 3-1). Signal conditioning circuitry,
such as the filters and attenuators described in
and
later in this chapter, can be used.
Connecting Ground-Referenced Signal Sources
