Chapter 3
Connecting the Signals
©
National Instruments Corporation
3-3
SCXI-1141/1142/1143 User Manual
Front Connector Signal Descriptions
Analog Input Channels
The SCXI-1141/1142/1143 module instrumentation amplifiers can reject
any common-mode voltage within their common-mode input range caused
by ground-potential differences between the signal source and the module.
In addition, the amplifiers can reject common-mode noise pickup in the
leads connecting the signal sources to the SCXI-1141/1142/1143 module.
However, you should take care to minimize noise pickup. The
common-mode rejection of the instrumentation amplifiers decreases
significantly at high frequencies. The amplifiers do not reject
normal-mode noise.
The maximum differential input voltage range of the
SCXI-1141/1142/1143 module instrumentation amplifiers is a function of
the gain of the amplifiers,
G
, and is equal to 5 V/
G
. The common-mode
input range of the SCXI-1141/1142/1143 module, however, is not a
function of gain—the differential input amplifier rejects common-mode
signals as long as the signal at both inputs is within
±
5 V of the module
Pins
Signal Names
Description
A32, A30, A26, A24,
A20, A18, A14, A12
IN+<0..7+>
Positive input channels—these pins connect to the
noninverting inputs of the instrumentation amplifier
of each channel.
C32, C30, C26, C24,
C20, C18, C14, C12
IN–<0..7–>
Negative input channels—these pins connect to the
inverting inputs of the instrumentation amplifier of
each channel.
A28, A22, A16, C28,
C22, C16
AGND
Analog ground—these pins connect to the module
analog ground.
A2, C8
DGND
Digital ground—these pins connect to the module
digital ground.
A8,A6, A4, C8
RSVD
Reserved—do not connect any signals to these pins.
C4
EXTCLK
External clock—you can use this signal to set the
filter cutoff frequency.
C2
OUTCLK
Output clock—this signal has a frequency that is
proportional to the cutoff frequency. You can use this
signal to external control the cutoff frequency.
Note:
All other pins are not connected.
