National Instruments NI 9234E User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9234E
4-Channel, ±5 V, 24-Bit Software-Selectable IEPE and
AC/DC Analog Input Module

2|ni.com |NI 9234E Operating Instructions and Specifications
This document describes how to use the National Instruments 9234E
and includes dimensions, connector assignments, and specifications
for the NI 9234E. 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 9234E. The end-product
supplier is responsible for conformity to any and all
compliance requirements.
Caution The NI 9234E must be installed inside a suitable
enclosure prior to use. Hazardous voltages may be present.
Caution Do not operate the NI 9234E in a manner not
specified in these operating instructions. 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.

NI 9234E Operating Instructions and Specifications|© National Instruments |3
NI 9234E Dimensions
The following figure shows the dimensions of the NI 9234E.
Figure 1. NI 9234E Dimensions in Millimeters (Inches)
73.38 (2.889)
4x Ø 3.18 (0.125)
7.33 (0.289)
0.00 (0.000)
0.00 (0.000)
–7.62 (–0.300)
–39.37 (–1.550) –52.96 (–2.085) –66.04 (–2.600) –87.43(–3.442)

4|ni.com |NI 9234E Operating Instructions and Specifications
Connecting the NI 9234E
The NI 9234E has four BNC connectors that provide connections
to four simultaneously sampled analog input channels.
Figure 2. NI 9234E Connector Assignments
AI0+
AI0–
AI1+
AI1–
AI2+
AI2–
AI3+
AI3–

NI 9234E Operating Instructions and Specifications|© National Instruments |5
Each channel has a BNC connector to which you can connect
a signal source. You can also enable excitation current on a
per-channel basis to connect Integrated Electronics Piezoelectric
(IEPE) sensors. Refer to the NI 9234E 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 9234E
You can connect ground-referenced or floating signal sources to
the NI 9234E. 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 you make a ground-referenced connection between the signal
source and the NI 9234E, make sure the voltage on the AI- shell
is in the common-mode range to ensure proper operation of the
NI 9234E. 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.

6|ni.com |NI 9234E Operating Instructions and Specifications
Refer to Figures 3 and 4 for illustrations of connecting grounded
and floating signal sources to the NI 9234E.
Figure 3. Connecting a Grounded Signal Source to the NI 9234E
NI 9234E
AI+
AI–
+
–
Signal
Source
Common
Mode
Voltage

NI 9234E Operating Instructions and Specifications|© National Instruments |7
Figure 4. Connecting a Floating Signal Source to the NI 9234E
The NI 9234E 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 9234E
results in a floating connection even though the case of the sensor
is grounded.
NI 9234E
AI+
AI–
+
–
Signal
Source

8|ni.com |NI 9234E Operating Instructions and Specifications
NI 9234E Circuitry
The NI 9234E 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. You can configure each channel in software for AC or DC
coupling. For channels set to AC coupling, you can turn the IEPE
excitation current on or off. Refer to the software help for
information about configuring channels on the NI 9234E.

NI 9234E Operating Instructions and Specifications|© National Instruments |9
Figure 5. NI 9234E Input Circuitry for One Channel
The NI 9234E uses common-mode bias current to bias the
current-limiting diodes when IEPE current is turned off. When the
NI 9234E 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 9234E
Common
Mode
Bias
Current
Current
Limiting
Diodes
50 Ω

10 |ni.com |NI 9234E Operating Instructions and Specifications
Figure 6. Measurement Error Introduced by Common-Mode Bias Current
The NI 9234E also has TEDS circuitry. For more information
about TEDS, go to ni.com/info and enter rdteds.
Understanding NI 9234E Filtering
The NI 9234E 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.
NI 9234E
AI+
AI–
+
–
Signal
Source
AI– Lead
Impedance
Common
Mode
Bias
Current

NI 9234E Operating Instructions and Specifications|© National Instruments |11
The NI 9234E 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 9234E 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 9234E.

12 |ni.com |NI 9234E Operating Instructions and Specifications
Figure 7. NI 9234E Typical Passband Flatness
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
Frequency/DataRate
0.50.4
0.025
0.000
–0.025
–0.050
0.30.20.10
Gain (dB)

NI 9234E Operating Instructions and Specifications|© National Instruments |13
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 9234E
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.
Understanding NI 9234E Data Rates
The frequency of a master timebase (fM) controls the data rate (fs)
of the NI 9234E. The NI 9234E 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 9234E 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 9234E. Visit ni.com/info and enter
cseriesdoc for information about C Series documentation.

14 |ni.com |NI 9234E Operating Instructions and Specifications
The following equation provides the available data rates of the
NI 9234E:
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 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 9234E 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 9234E Operating Instructions and Specifications|© National Instruments |15
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.

16 |ni.com |NI 9234E Operating Instructions and Specifications
Specifications
The following specifications are typical for the range -40 °C to 85 °C
internal to any enclosures 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

NI 9234E Operating Instructions and Specifications|© National Instruments |17
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 9234E Data Rates section for more information.
fM256÷
n
---------------------

18|ni.com |NI 9234E Operating Instructions and Specifications
AC cutoff frequency response
Input range ........................................ ±5 V
Frequency (Hz)
104
0.5
0.0
–0.5
–1.0
321098765
Gain (dB)

NI 9234E Operating Instructions and Specifications|© National Instruments |19
AC voltage full-scale range
Minimum .................................... ±5 Vpk
Typical ........................................ ±5.1 Vpk
Maximum ................................... ±5.2 Vpk
Common-mode voltage range
(AI- to earth ground)......................... ±2 V max
IEPE excitation current (software-selectable on/off)
Minimum .................................... 2.0 mA
Typical ........................................ 2.1 mA
Power-on glitch................................. 90 μA for 10 μs