OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9233
4-Channel, ±5 V, 24-Bit IEPE Analog Input Module
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ni.com/manuals
This document describes how to use the National Instruments 9233
and includes specifications and connector assignments for the
NI 9233. 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
and enter
cseriesdoc for information about C Series
ni.com/info
documentation.
Note The safety guidelines and specifications in this
document are specific to the NI 9233. 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. Visit
ni.com/info and enter cseriesdoc for information
about C Series documentation.
NI 9233 Operating Instructions and Specifications 2 ni.com
Safety Guidelines
Operate the NI 9233 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.
Safety Guidelines for Hazardous Locations
The NI 9233 is suitable for use in Class I, Division 2, Groups A, B,
C, D, T 4 ha zar dous locations; Class I, Zone 2, AEx nC IIC T4, and
Ex nC IIC T4 hazardous locations; and nonhazardous locations
only. Follow these guidelines if you are installing the NI 9233 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.
© National Instruments Corp. 3 NI 9233 Operating Instructions and Specifications
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.
Caution For Zone 2 applications, connected signals must
be within the following limit:
Capacitance .......................... 0.2 μF max
Special Conditions for Hazardous Locations Use in Europe
This equipment has been evaluated as EEx nC IIC T4 equipment
under DEMKO Certificate No. 03 ATEX 0324020X. Each module
is marked II 3G and is suitable for use in Zone 2 hazardous
locations. If you are using the NI 9233 in Gas Group IIC hazardous
locations or in ambient temperatures of –40 °C ≤ Ta ≤ 70 °C, you
must use the device in an NI chassis that has been evaluated as
EEx nC IIC T4, Ex nA IIC T4, or Ex nL IIC T4 equipment.
NI 9233 Operating Instructions and Specifications 4 ni.com
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.
© National Instruments Corp. 5 NI 9233 Operating Instructions and Specifications
Connecting the NI 9233
The NI 9233 has four BNC connectors that provide connections for
four simultaneously sampled analog input channels.
AI0+
AI0–
AI1+
AI1–
AI2+
AI2–
AI3+
AI3–
Figure 1. NI 9233 Connector Assignments
NI 9233 Operating Instructions and Specifications 6 ni.com
Each channel has a BNC connector to which you can connect an
Integrated Electronic Piezoelectric (IEPE) sensor. The center pin
of the connector, AI+, provides the DC excitation and the AC
signal connection. The shell of the connector, AI–, provides the
excitation return path and the AC signal ground reference.
Yo u can connect ground-referenced or floating IEPE sensors to the
NI 9233. You can avoid picking up ground noise by using a floating
connection. Typical IEPE sensors have a case that is electrically
isolated from the IEPE electronics, so connecting the sensor to the
NI 9233 results in a floating connection even though the case of the
sensor is grounded. To further minimize ground noise, prevent
the metal shells of the BNC connectors from touching each other,
the modules, or the chassis.
If you make a ground-referenced connection between the IEPE
sensor and the NI 9233, make sure the voltage on the AI– shell
is in the common-mode range to ensure proper operation of the
NI 9233. The AI– shell is protected against accidental contact
with overvoltages within the overvoltage protection range. Refer
to the Specifications section for more information about operating
voltages and overvoltage protection. Figures 2 and 3 illustrate
connecting grounded and floating IEPE sensors to the NI 9233.
© National Instruments Corp. 7 NI 9233 Operating Instructions and Specifications
IEPE Sensor
+
–
AI+
AI–
NI 9233
Figure 2. Connecting a Grounded IEPE Sensor to the NI 9233
IEPE Sensor
AI+
+
–
AI–
NI 9233
Figure 3. Connecting a Floating IEPE Sensor to the NI 9233
NI 9233 Operating Instructions and Specifications 8 ni.com
The NI 9233 analog input channels are referenced to the chassis
ground through a 50 Ω resistor. To minimize ground noise, make
sure that the chassis ground is connected to the earth ground. Each
channel is protected from overvoltages. The NI 9233 provides
an IEPE excitation current for each input signal. The signal is
AC-coupled, buffered, and conditioned. The signal is then sampled
by a 24-bit Delta-Sigma ADC. The NI 9233 IEPE excitation
current and AC coupling are always enabled. Refer to Figure 4 for
an illustration of the input circuitry for one channel of the NI 9233.
Excitation
Current
AC
AI+
AI–
50 Ω
Figure 4. Input Circuitry for One Channel of the NI 9233
© National Instruments Corp. 9 NI 9233 Operating Instructions and Specifications
Coupling
+
Amplifier
and
Prefilter
ADC
NI 9233
The NI 9233 also has TEDS circuitry. For more information about
TEDS, visit
ni.com/info and enter rdteds.
Understanding NI 9233 Filtering
The NI 9233 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 9233 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 9233 adjust the frequency range of the passband to match the
data rate. Therefore, the amount of gain or attenuation at a given
NI 9233 Operating Instructions and Specifications 10 ni.com
frequency depends on the data rate. Figure 5 shows typical
passband flatness for data rates above 25.65 kS/s and less than
or equal to 25.65 kS/s.
0.025
Data Rate
> 25.65 kS/s
0.000
Gain (dB)
–0.025
Data Rate
≤
25.65 kS/s
–0.050
0.30. 20.10
Frequency/Data Rate
0.50.4
Figure 5. Typical Passband Flatness for the NI 9233
© National Instruments Corp. 11 NI 9233 Operating Instructions and Specifications
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