Chapter 2
Using the NI 447X
2-10
ni.com
Input Polarity and Input Range
Caution
Connections that exceed the rated input voltages can damage the computer and
the connected equipment. Overvoltage protection is ±42.4 V on the positive signal line.
The shield does
not
have overvoltage protection. Do
not
make a non-ground connection to
the shield. Also, do
not
connect the shield to a ground that varies more than ±2.5 V from
the ground of the NI 447
X
. NI is
not
liable for any damages resulting from such
connections.
The NI 447
X
analog inputs are bipolar; that is, the input voltage range is
centered on 0 V. The input voltage range is ±10 V with 2.38
µ
V resolution,
and is always at a gain of 1.0 (0 dB). Due to the large dynamic range of
the ADC used on the NI 447
X
, programmable gain is not required for most
applications. Since the NI 447
X
does not have hardware to adjust the input
gain, the component count in the input signal path is reduced, resulting in
less noise and distortion. If the input signal has an amplitude greater than
±10 V, it is clipped and introduces large errors that can be easily identified
in the frequency spectrum or by using the digital overload detection feature
of the NI 447
X
.
All data read from the ADC are interpreted as two’s complement format.
In two’s complement mode, digital data values read from the analog input
channel are either positive or negative.
Digital Trigger
You can use the
EXT TRIG
SMB connector on the NI 447
X
for external
digital triggering.
Using Test Panels to Acquire a Signal
To quickly test signal connections and the operation of the system, you can
use the Test Panels to view a signal input to the NI 447
X
. To do so,
complete the following steps:
1.
Connect a known signal to an AI channel on the NI 447
X
.
2.
Launch Measurement & Automation Explorer (MAX) from the
desktop.
3.
Open the
Devices and Interfaces
folder.
4.
Right-click the icon for the NI 447
X
device you want to test and select
Test Panel
from the pop-up dialog.
