National Instruments NI 9225E User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9225E
3-Channel, 300 Vrms, 24-Bit, Simultaneous,
Channel-to-Channel Isolated Analog Input Module

NI 9225E Operating Instructions and Specifications 2 ni.com
This document describes how to use the National
Instruments 9225E and includes dimensions, terminal assignments,
and specifications for the NI 9225E. Visit ni.com/info and enter
rdsoftwareversion to determine which software you need for
the modules you are using. For information about installing,
configuring, and programming the system, refer to the system
documentation. Visit
ni.com/info and enter cseriesdoc for
information about C Series documentation.
Caution National Instruments makes no electromagnetic
compatibility (EMC) or CE marking compliance claims
for the NI 9225E. The end-product supplier is responsible
for conformity to any and all compliance requirements.
Caution The NI 9225E must be installed inside a suitable
enclosure prior to use. Hazardous voltages may be present.

© National Instruments Corp. 3 NI 9225E Operating Instructions and Specifications
NI 9225E Dimensions
The following figure shows the dimensions of the NI 9225E.
Figure 1. NI 9225E Dimensions in Millimeters (Inches)
73.4 (2.89)
0.0 (0.00)
26.7 (1.05)
58.4 (2.30)
66.0 (2.60)
0.0 (0.00)

NI 9225E Operating Instructions and Specifications 4 ni.com
Connecting the NI 9225E
The NI 9225E has three 2-terminal detachable screw-terminal
connectors that provide connections for three simultaneously
sampled, isolated analog input channels.
Figure 2. NI 9225E Terminal Assignments
AI0+
AI0–
AI1+
AI1–
AI2+
AI2–
0
1
0
1
0
1

© National Instruments Corp. 5 NI 9225E Operating Instructions and Specifications
You can connect ground-referenced or floating signal sources to
the NI 9225E. Connect the positive signal of the signal source to
the AI+ terminal, and connect the negative signal of the signal
source to the AI– terminal. If you make a ground-referenced
connection between the signal source and the NI 9225E, make sure
the voltage on the AI+ and AI– connections are in the
channel-to-earth safety voltage range to ensure proper operation of
the NI 9225E. Refer to the Specifications section for more
information about operating voltages and overvoltage protection.
Note You must use 2-wire ferrules to create a secure
connection when connecting more than one wire to a
single terminal on the NI 9225E.
Refer to Figures 3 and 4 for illustrations of how to connect
grounded and floating signal sources to the NI 9225E.

NI 9225E Operating Instructions and Specifications 6 ni.com
Figure 3. Connecting a Grounded Signal Source to the NI 9225E
Figure 4. Connecting a Floating Signal Source to the NI 9225E
NI 9225E
Signal
Source
AI–
+
–
AI+
NI 9225E
Signal
Source
AI–
+
–
AI+

© National Instruments Corp. 7 NI 9225E Operating Instructions and Specifications
The NI 9225E analog input channels are floating with respect to
earth ground and each other. The incoming analog signal on each
channel is conditioned, buffered, and then sampled by a 24-bit
Delta-Sigma ADC.
Each channel provides an independent signal path and ADC,
enabling you to sample all three channels simultaneously. Refer to
Figure 5 for an illustration of the circuitry for one channel of
the NI 9225E.
Figure 5. Input Circuitry for One Channel of the NI 9225E
NI 9225E
AI+
AI–
ADC
Amplifier
Overvoltage
Protection
Prefilter

NI 9225E Operating Instructions and Specifications 8 ni.com
Understanding NI 9225E Filtering
The NI 9225E uses a combination of analog and digital filtering
to provide an accurate representation of in-band signals while
rejecting out-of-band signals. The filters discriminate between
signals based on the frequency range, or bandwidth, of the signal.
The three important bandwidths to consider are the passband, the
stopband, and the alias-free bandwidth.
The NI 9225E represents signals within the passband, as quantified
primarily by passband flatness and phase nonlinearity. All signals
that appear in the alias-free bandwidth are either unaliased signals
or signals that have been filtered by at least the amount of the
stopband rejection.
Passband
The signals within the passband have frequency-dependent gain or
attenuation. The small amount of variation in gain with respect to
frequency is called the passband flatness. The digital filters of the
NI 9225E adjust the frequency range of the passband to match the
data rate. Therefore, the amount of gain or attenuation at a given
frequency depends on the data rate. Figure 6 shows typical
passband flatness for the NI 9225E.

© National Instruments Corp. 9 NI 9225E Operating Instructions and Specifications
Figure 6. Typical Passband Response of the NI 9225E
Frequency/Data Rate
0.50.4
0.025
0.000
–0.025
–0.050
0.30.20.10
Gain (dB)

NI 9225E Operating Instructions and Specifications 10 ni.com
Stopband
The filter significantly attenuates all signals above the stopband
frequency. The primary goal of the filter is to prevent aliasing.
Therefore, the stopband frequency scales precisely with the data
rate. The stopband rejection is the minimum amount of attenuation
applied by the filter to all signals with frequencies within the
stopband.
Alias-Free Bandwidth
Any signal that appears in the alias-free bandwidth of the
NI 9225E is not an aliased artifact of signals at a higher frequency.
The alias-free bandwidth is defined by the ability of the filter to
reject frequencies above the stopband frequency and equals the
data rate minus the stopband frequency.
Understanding NI 9225E Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9225E. The NI 9225E includes an internal master
timebase with a frequency of 12.8 MHz, but the module also can
accept an external master timebase or export its own master
timebase. To synchronize the data rate of an NI 9225E with other
modules that use master timebases to control sampling, all of the