National Instruments NI 9234 User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9234
4-Channel, ±5 V, 24-Bit Software-Selectable
IEPE and AC/DC Analog Input Module
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NI 9234 Operating Instructions and Specifications 2ni.com
This document describes how to use the National Instruments 9234
and includes specifications and connector assignments for the
NI 9234. Visit ni.com/info and enter rdsoftwareversion to
determine which software youneed for the modules youare 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.
Note The safety guidelines and specifications in this
document are specific to the NI 9234. 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.

© National Instruments Corp. 3 NI 9234 Operating Instructions and Specifications
Safety Guidelines
Operate the NI 9234 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 9234 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 youare installing the NI 9234 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.

NI 9234 Operating Instructions and Specifications 4ni.com
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 Ex nA IIC T4 equipment
under DEMKO Certificate No. 07 ATEX 0626664X. Each module
is marked II 3G and is suitable for use in Zone 2 hazardous
locations. If youare using the NI 9234 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.

© National Instruments Corp. 5 NI 9234 Operating Instructions and Specifications
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.

NI 9234 Operating Instructions and Specifications 6ni.com
Connecting the NI 9234
The NI 9234 has four BNC connectors that provide connections to
four simultaneously sampled analog input channels.
Figure 1. NI 9234 Connector Assignments
AI3+
AI3–
AI2+
AI2–
AI0+
AI0–
AI1+
AI1–

© National Instruments Corp. 7 NI 9234 Operating Instructions and Specifications
Each channel has a BNC connector to which youcan connect
a signal source. Youcan also enable excitation current on a
per-channel basis to connect Integrated Electronics Piezoelectric
(IEPE) sensors. Refer to the NI 9234 Circuitry section for more
information. The center pin of the connector, AI+, provides the DC
excitation, when enabled, and the positive input signal connection.
The shell of the connector, AI–, provides the excitation return path
and the signal ground reference.
Connecting Signal Sources to the NI 9234
Yo ucan connect ground-referenced or floating signal sources to
the NI 9234. To avoid picking up ground noise, use a floating
connection. To further minimize ground noise, prevent the metal
shells of the BNC connectors from coming in contact with each
other, the modules, or the chassis.
If youmake a ground-referenced connection between the signal
source and the NI 9234, make sure the voltage on the AI– shell
is in the common-mode range to ensure proper operation of the
NI 9234. 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.

NI 9234 Operating Instructions and Specifications 8ni.com
Refer to Figures 2 and 3 for illustrations of connecting grounded
and floating signal sources to the NI 9234.
Figure 2. Connecting a Grounded Signal Source to the NI 9234
NI 9234
AI+
AI–
+
–
Signal
Source
Common
Mode
Voltage

© National Instruments Corp. 9 NI 9234 Operating Instructions and Specifications
Figure 3. Connecting a Floating Signal Source to the NI 9234
The NI 9234 can also provide an IEPE excitation current for each
channel to measure ground-referenced or floating IEPE sensors.
Typical IEPE sensors have a case that is electrically isolated from
the IEPE electronics, so connecting the sensor to the NI 9234
results in a floating connection even though the case of the sensor
is grounded.
NI 9234
AI+
AI–
+
–
Signal
Source

NI 9234 Operating Instructions and Specifications 10 ni.com
NI 9234 Circuitry
The NI 9234 analog input channels are referenced to chassis
ground through a 50 Ωresistor. To minimize ground noise, make
sure the chassis ground is connected to earth ground. Each channel
is protected from overvoltages. The input signal on each channel is
buffered, conditioned, and then sampled by a 24-bit Delta-Sigma
ADC. Youcan configure each channel in software for AC or DC
coupling. For channels set to AC coupling, youcan turn the IEPE
excitation current on or off. Refer to the software help for
information about configuring channels on the NI 9234.

© National Instruments Corp. 11 NI 9234 Operating Instructions and Specifications
Figure 4. NI 9234 Input Circuitry for One Channel
The NI 9234 uses common-mode bias current to bias the
current-limiting diodes when IEPE current is turned off. When the
NI 9234 is using grounded signal sources, this current causes an
error that is dependent on the AI– lead impedance. This error is
approximately 50 ppm of range and 15 ppm of reading per Ωof
AI– impedance. The common-mode bias current causes an error
only with grounded sources and is not an issue with floating signal
sources. For best accuracy, use a floating connection or use
low-impedance leads when connecting grounded signal sources.
2 mA IEPE on/off
AI+
AI–
Amplifier
and
Prefilter
ADC
+
–
AC/DC Coupling
NI 9234
Common
Mode
Bias
Current
Current
Limiting
Diodes
50 Ω

NI 9234 Operating Instructions and Specifications 12 ni.com
Figure 5. Measurement Error Introduced by Common-Mode Bias Current
The NI 9234 also has TEDS circuitry. For more information about
TEDS, go to ni.com/info and enter rdteds.
NI 9234
AI+
AI–
+
–
Signal
Source
AI– Lead
Impedance
Common
Mode
Bias
Current

© National Instruments Corp. 13 NI 9234 Operating Instructions and Specifications
Understanding NI 9234 Filtering
The NI 9234 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 9234 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 9234 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 9234.

NI 9234 Operating Instructions and Specifications 14 ni.com
Figure 6. NI 9234 Typical Passband Flatness
Frequency/Data Rate
0.50.4
0.025
0.000
–0.025
–0.050
0.30.20.10
Gain (dB)

© National Instruments Corp. 15 NI 9234 Operating Instructions and Specifications
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 9234
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 it is equal to the
data rate minus the stopband frequency.

NI 9234 Operating Instructions and Specifications 16 ni.com
Understanding NI 9234 Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9234. The NI 9234 includes an internal master timebase
with a frequency of 13.1072 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 9234 with other modules that use
master timebases to control sampling, all of the modules must
share a single master timebase source. Refer to the software help
for information about configuring the master timebase source for
the NI 9234. Visit ni.com/info and enter cseriesdoc for
information about C Series documentation.
The following equation provides the available data rates of the
NI 9234:
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
f
M256÷
n
---------------------

© National Instruments Corp. 17 NI 9234 Operating Instructions and Specifications
of 13.1072 MHz, the result is data rates of 51.2 kS/s, 25.6 kS/s,
17.067 kS/s, and so on down to 1.652 kS/s, depending on the value
of n. When using an external timebase with a frequency other than
13.1072 MHz, the NI 9234 has a different set of data rates.
Note The cRIO-9151 R Series Expansion chassis does
not support sharing timebases between modules.
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, youcannot
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.

NI 9234 Operating Instructions and Specifications 18 ni.com
Specifications
The following specifications are typical for the range –40 to 70 °C
unless otherwise noted.
Input Characteristics
Number of channels .......................... 4 analog input channels
ADC resolution ................................. 24 bits
Type of ADC..................................... Delta-Sigma
(with analog prefiltering)
Sampling mode ................................. Simultaneous
Type of TEDS supported .................. IEEE 1451.4 TEDS Class I
Internal master timebase (fM)
Frequency ................................... 13.1072 MHz
Accuracy..................................... ±50 ppm max
Data rate range (fs) using internal master timebase
Minimum.................................... 1.652 kS/s
Maximum ................................... 51.2 kS/s

© National Instruments Corp. 19 NI 9234 Operating Instructions and Specifications
Data rate range (fs) using external master timebase
Minimum.................................... 0.391 kS/s
Maximum ................................... 52.734 kS/s
Data rates1(fs)................................... , n= 1, 2, …, 31
Input coupling................................... AC/DC (software-selectable)
AC cutoff frequency
–3 dB .......................................... 0.5 Hz
–0.1 dB....................................... 4.6 Hz max
1 The data rate must remain within the appropriate data rate range. Refer to the
Understanding NI 9234 Data Rates section for more information.
f
M256÷
n
---------------------

NI 9234 Operating Instructions and Specifications 20 ni.com
AC cutoff frequency response
Frequency (Hz)
104
0.5
0.0
–0.5
–1.0
321098765
Gain (dB)