Chapter 2
Configuration and Installation
2-6
©
National Instruments Corporation
Configure the host MIO board for differential inputs if you plan to use this
temperature sensor. Use jumper W1 to select either the temperature sensor
or the external screw terminals as the input source for differential
channel 0. The AMUX-64T is shipped from the factory with the jumpers
set so that CH0 and CH32 are connected to the terminal block (the
temperature sensor is not selected).
Shield Selection
The AMUX-64T is shipped from the factory with the jumpers set so that
AIGND and CABLE SHLD are disconnected from CHASSIS. Table 2-3
shows the jumper W2 and jumper W3 settings.
The AMUX-64T has two optional connections that are relevant when using
a rack-mount kit to mount the AMUX-64T, jumpers W2 and W3.
Jumper W2 connects the analog input ground (AIGND) to the rack-mount
kit. Setting this jumper to the AIGND position connects the AIGND signal
to the metal standoff in the lower left corner of the board. Setting this
jumper to the NC position keeps the AMUX-64T AIGND isolated from the
rack.
Jumper W3 connects the shield of the 68-position connector to the
rack-mount kit. Setting this jumper to the CABLE SHLD position connects
the shield of the 68-position connector to the metal standoff in the lower left
corner of the board. Setting this jumper to the NC position keeps the
computer chassis isolated from the rack.
Both jumpers’ ground configurations may or may not be desired for your
application.
For most applications, you should not connect the grounds together with
these jumpers. Connecting jumper W3 may cause ground currents to flow
between the computer chassis and the rack-mount chassis. These currents
are likely to couple noise into the analog signals in the cabling. Connecting
jumper W2 may cause ground currents to flow between the MIO board
AIGND signal (measurement ground) and the rack-mount chassis. These
currents directly interfere with measurements made with the analog signals,
especially when the MIO board is in RSE mode.
If the rack-mount chassis is floating (that is, not earth-grounded),
you should ground it. Ground the rack via a ground strap or other
recommended ways. You may ground it using jumper W3. In general,
you will get the best results if all grounds and shields have exactly one
conduction path to earth ground.