National Instruments NI 9225 User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9225
3-Channel, 300 Vrms, 24-Bit Simultaneous,
Channel-to-Channel Isolated Analog Input Module
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2|ni.com |NI 9225 Operating Instructions and Specifications
This document describes how to use the National Instruments 9225
and includes specifications and pin assignments for the NI 9225.
Note The safety guidelines and specifications in this
document are specific to the NI 9225. The other
components in the system might not meet the same safety
ratings and specifications. Refer to the documentation for
each component in the system to determine the safety
ratings and specifications for the entire system.
Related Information
Services
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NI CompactDAQ &
NI CompactRIO Documentation
ni.com/info cseriesdoc
ni.com/info softwareversion
Chassis Compatibility
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Software Support

NI 9225 Operating Instructions and Specifications |© National Instruments |3
Safety Guidelines
Operate the NI 9225 only as described in these operating
instructions.
Hot Surface This icon denotes that the component may
be hot. Touching this component may result in bodily
injury.
Hazardous Voltage This icon denotes a warning
advising you to take precautions to avoid electrical
shock.
Caution Do not operate the NI 9242 in a manner not
specified in this manual. Product misuse can result in a
hazard. You can compromise the safety protection built
into the product if the product is damaged in any way. If
the product is damaged, return it to National Instruments
for repair.
Safety Guidelines for Hazardous Voltages
If hazardous voltages are connected to the module, take the
following precautions. A hazardous voltage is a voltage greater
than 42.4 Vpk or 60 VDC to earth ground.

4|ni.com |NI 9225 Operating Instructions and Specifications
Caution Ensure that hazardous voltage wiring is
performed only by qualified personnel adhering to local
electrical standards.
Caution Do not mix hazardous voltage circuits and
human-accessible circuits on the same module.
Caution Make sure that devices and circuits connected
to the module are properly insulated from human contact.
Caution When module terminals are hazardous voltage
LIVE (>42.4 Vpk/60 VDC), you must ensure that devices
and circuits connected to the module are properly
insulated from human contact. You must use the NI 9971
connector backshell kit to ensure that the terminals are
not accessible.

NI 9225 Operating Instructions and Specifications |© National Instruments |5
Figure 1 shows the NI 9971 connector backshell.
Figure 1. NI 9971 Connector Backshell

6|ni.com |NI 9225 Operating Instructions and Specifications
Safety Guidelines for Hazardous Locations
The NI 9225 is suitable for use in Class I, Division 2, Groups A, B,
C, D, T4 hazardous locations; Class I, Zone 2, AEx nA IIC T4, and
Ex nA IIC T4 hazardous locations; and nonhazardous locations
only. Follow these guidelines if you are installing the NI 9225 in a
potentially explosive environment. Not following these guidelines
may result in serious injury or death.
Caution Do not disconnect I/O-side wires or connectors
unless power has been switched off or the area is known
to be nonhazardous.
Caution Do not remove modules unless power has been
switched off or the area is known to be nonhazardous.
Caution Substitution of components may impair
suitability for Class I, Division 2.
Caution For Zone 2 applications, install the system
in an enclosure rated to at least IP 54 as defined by
IEC 60529 and EN 60529.

NI 9225 Operating Instructions and Specifications |© National Instruments |7
Special Conditions for Marine Applications
Some modules are Lloyd’s Register (LR) Type Approved for
marine applications. To verify Lloyd’s Register certification, visit
ni.com/certification and search for the LR certificate, or
look for the Lloyd’s Register mark on the module.
Caution To meet radio frequency emission
requirements for marine applications, use shielded cables
and install the system in a metal enclosure. Suppression
ferrites must be installed on power supply inputs near
power entries to modules and controllers. Power supply
and module cables must be separated on opposite sides of
the enclosure and must enter and exit through opposing
enclosure walls.

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

NI 9225 Operating Instructions and Specifications |© National Instruments |9
You can connect ground-referenced or floating signal sources to
the NI 9225. 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 9225, 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 9225. 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 9225.

10 |ni.com |NI 9225 Operating Instructions and Specifications
Refer to Figures 3 and 4 for illustrations of how to connect
grounded and floating signal sources to the NI 9225.
Figure 3. Connecting a Grounded Signal Source to the NI 9225
Figure 4. Connecting a Floating Signal Source to the NI 9225
NI 9225
Signal
Source
AI–
+
–
AI+
NI 9225
Signal
Source
AI–
+
–
AI+

NI 9225 Operating Instructions and Specifications |© National Instruments |11
The NI 9225 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 9225.
Figure 5. Input Circuitry for One Channel of the NI 9225
NI 9225
AI+
AI–
ADC
Amplifier
Overvoltage
Protection
Prefilter

12 |ni.com |NI 9225 Operating Instructions and Specifications
Wiring for High-Vibration Applications
If an application is subject to high vibration, National Instruments
recommends that you either use ferrules to terminate wires to the
detachable screw-terminal connector or use the NI 9971 backshell
kit to protect the connections. Refer to Figure 6 for an illustration
of using ferrules. Refer to Figure 1 for an illustration of the
NI 9971 connector backshell.
Figure 6. 2-Terminal Detachable Screw-Terminal Connector with Ferrule

NI 9225 Operating Instructions and Specifications |© National Instruments |13
Understanding NI 9225 Filtering
The NI 9225 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 9225 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 9225 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 7 shows typical
passband flatness for the NI 9225.

14 |ni.com |NI 9225 Operating Instructions and Specifications
Figure 7. Typical Passband Response of the NI 9225
Frequency/DataRate (Hz)
0.50.4
0.025
0.000
–0.025
–0.050
0.30.20.10
Gain (dB)

NI 9225 Operating Instructions and Specifications |© National Instruments |15
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 9225
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 9225 Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9225. The NI 9225 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 9225 with other modules that use
master timebases to control sampling, all of the modules must

16 |ni.com |NI 9225 Operating Instructions and Specifications
share a single master timebase source. Refer to the software help
for information about configuring the master timebase source for
the NI 9225. Visit ni.com/info and enter cseriesdoc for
information about C Series documentation.
The following equation provides the available data rates of the
NI 9225:
fs=
where nis any integer from 1 to 31.
However, the data rate must remain within the appropriate data rate
range. Refer to the Specifications section for more information
about the data rate range. When using the internal master timebase
of 12.8 MHz, the result is data rates of 50 kS/s, 25 kS/s,
16.667 kS/s, and so on down to 1.613 kS/s, depending on the value
of n. When using an external timebase with a frequency other than
12.8 MHz, the NI 9225 has a different set of data rates.
Note The cRIO-9151 R Series Expansion chassis does
not support sharing timebases between modules.
fM256÷
n
---------------------

NI 9225 Operating Instructions and Specifications |© National Instruments |17
Sleep Mode
This module supports a low-power sleep mode. Support for sleep
mode at the system level depends on the chassis that the module is
plugged into. Refer to the chassis manual for information about
support for sleep mode. If the chassis supports sleep mode, refer to
the software help for information about enabling sleep mode. Visit
ni.com/info and enter cseriesdoc for information about
C Series documentation.
Typically, when a system is in sleep mode, you cannot
communicate with the modules. In sleep mode, the system
consumes minimal power and may dissipate less heat than it does
in normal mode. Refer to the Specifications section for more
information about power consumption and thermal dissipation.

18 |ni.com |NI 9225 Operating Instructions and Specifications
Specifications
The following specifications are typical for the range -40 to 70 °C
unless otherwise noted. All voltages are relative to the AI- signal
on each channel unless otherwise noted.
Input Characteristics
Number of channels.......................... 3 analog input channels
ADC resolution................................. 24 bits
Type of ADC..................................... Delta-Sigma (with analog
prefiltering)
Sampling mode ................................. Simultaneous
Internal master timebase (fM)
Frequency ................................... 12.8 MHz
Accuracy..................................... ±100 ppm max
Data rate range (fs) using internal master timebase
Minimum.................................... 1.613 kS/s
Maximum ................................... 50 kS/s

NI 9225 Operating Instructions and Specifications |© National Instruments |19
Data rate range (fs) using external master timebase
Minimum.................................... 390.625 S/s
Maximum ................................... 51.36 kS/s
Data rates1(fs) ................................... , n = 1, 2, ..., 31
Operating voltage ranges2
Minimum.................................... 294 Vrms
Typical........................................ 300 Vrms
Typical scaling coefficient ................ 50.66 µV/LSB
Overvoltage protection ..................... ±450 VDC
Input coupling................................... DC
Input impedance (AI+ to AI-)........... 1 MΩ
1 The data rate must remain within the appropriate data rate range. Refer to the
Understanding NI 9225 Data Rates section for more information.
2 Refer to the Safety Guidelines section for more information about safe operating
voltages.
fM256÷
n
---------------------

20 |ni.com |NI 9225 Operating Instructions and Specifications
Accuracy
Input noise ........................................ 2 mVrms
Stability
Gain drift .................................... ±10 ppm/°C
Offset drift .................................. ±970 µV/°C
Post calibration gain match
(ch-to-ch, 20 kHz)............................. ±0.25 dB max
Measurement Conditions
Percent of
Reading
(Gain Error)
Percent of
Range*
(Offset Error)
Calibrated max (-40 to 70 °C) ±0.23% ±0.05%
Calibrated typ (25 °C, ±5 °C) ±0.05% ±0.008%
Calibrated max (25 °C, ±15 °C) ±0.084% ±0.016%
Uncalibrated max (-40 to 70 °C) ±1.6% ±0.66%
Uncalibrated typ (25 °C, ±5 °C) ±0.4% ±0.09%
*Range equals 425 V.