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