Chapter 1
BNC-2090A Overview
©
National Instruments Corporation
1-7
all devices connected to it, and the host computer. Overvoltage can also cause an electric
shock hazard for the operator. National Instruments is
not
liable for damage or injury
resulting from such misuse.
Setting the BNC-2090A Shield Ground Jumper
The BNC-2090A shield ground jumper, labeled W1 on the PCB, is
factory-configured to connect the shield of the 68-position connectors and
BNC-2090A metal case through a 100
Ω
resistor to D GND.
You must reconfigure the jumper if you want to connect the BNC-2090A
shield directly to digital ground (D GND).
Table 1-1 shows the shield ground jumper setting options.
To access and reconfigure the shield ground jumper, complete the
following steps while referring to Figure 1-5.
Table 1-1.
Shield Ground Jumper Settings
Setting
Description
100
Ω
to Digital Ground
—Use this setting to reduce any potential
ground loop current, thereby improving the system noise
performance. When the BNC-2090A is rack-mounted, it is connected
to a different ground.
This is the factory default setting.
Digital Ground
—Use this setting when the BNC-2090A metal case
is
not
connected to any other ground through a rack mount or
connected to the DAQ ground through a shielded cable. Use this
setting when using unshielded cables.
You can also disconnect the shield from the DAQ ground by removing
shield ground jumper, which prevents the ground loop current from
being carried in the D GND return of the shielded cable. This option
is best for rack-mount configurations where the BNC-2090A metal
case is already grounded.
R53
100
Ω
W1
Shield
Factory Default
R53
100
Ω
W1
Shield
R53
100
Ω
W1
Shield
