Manual - National Instruments

SCXI™-1304 AC/DC COUPLING TERMINAL BLOCK
INSTALLATION GUIDE
This guide describes how to install and use the National Instruments
SCXI-1304 AC/DC coupling terminal block with the SCXI-1140,
SCXI-1141/1142/1143, SCXI-1120/D, SCXI-1125, and SCXI-1126
modules.
The SCXI-1304 AC/DC is a shielded terminal block with screw terminals
that you can connect to the SCXI-1140, SCXI-1141/1142/1143,
SCXI-1120/D, SCXI-1125, or SCXI-1126 input connector. You can
configure each SCXI-1304 channel to provide AC or DC coupling of a
signal to the SCXI module, and each channel can ground reference a
floating signal with a bias resistor.
The terminal block has 22 screw terminals for easy signal connection. You
can use eight pairs of screw terminals for signal connections to the eight
module inputs and one pair to connect to the module analog ground. The
remaining four screw terminals provide access to the digital ground and
digital signals of the module. These signals are HOLDTRIG for the
SCXI-1140, and OUTCLK and EXTCLK for the SCXI-1141/1142/1143.
Conventions
The following conventions are used in this manual:
»
The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash. When this symbol is marked on
the product, refer to the Read Me First: Safety and Radio-Frequency
Interference document, shipped with the product, for precautions to take.
National Instruments™, NI™, ni.com™, and SCXI™ are trademarks of National Instruments Corporation. Product and
company names mentioned herein are trademarks or trade names of their respective companies. For patents covering
National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt file
on your CD, or ni.com/patents.
ni.com
© 1998–2003 National Instruments Corp. All rights reserved.
January 2003
321922B-01
bold
Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names.
italic
Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text that is a placeholder for a word
or value that you must supply.
monospace
Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
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programs, subprograms, subroutines, device names, functions, operations,
variables, filenames and extensions, and code excerpts.
What You Need to Get Started
To set up and use the SCXI-1304 terminal block, you need the following
items:
❑ SCXI-1304 AC/DC coupling terminal block
❑ SCXI-1304 AC/DC Coupling Terminal Block Installation Guide
❑ Read Me First: Safety and Radio-Frequency Interference
❑ SCXI chassis and documentation
❑ One of the following modules and its associated documentation:
–
SCXI-1140
–
SCXI-1141/1142/1143
–
SCXI-1120/D
–
SCXI-1125
–
SCXI-1126
❑ Numbers 1 and 2 Phillips screwdrivers
❑ 1/8 in. flathead screwdriver
❑ Long-nose pliers
❑ Wire cutter
❑ Wire insulation stripper
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Configuring Floating and Ground-Referenced Signals
Note You can use the SCXI-1304 terminal block with SCXI-1120/D, SCXI-1125,
and SCXI-1126 modules. However, when using these modules, the channel isolation
specification is invalid if the bias resistors are in the engaged position. You must leave
the resistor switches in the open or G grounded position to keep the isolation valid.
Signal sources are either floating sources or ground-referenced sources.
•
Floating signal source—does not connect in any way to the building
ground system and therefore has an isolated ground-reference point
that you cannot assume to be at the same potential as any other ground.
Examples of this source type include transformers, insulated
thermocouples, optical isolators, isolation amplifiers, and
battery-powered devices.
•
Ground-referenced signal source—connects to the building ground
and thus shares a common ground with the E Series data acquisition
(DAQ) device, assuming that the computer is also connected to the
building power supply and there are no ground loops. Examples of
ground-referenced signals are the nonisolated outputs of any devices
that plug into the building power supply, such as signal/function
generators and power supplies. Isolated outputs do not constitute
ground-referenced sources; treat them as floating sources.
In general, you should reference an input signal to ground at only one point.
Therefore, do not reference the input of a differential amplifier module to
ground if the signal source is already ground referenced. If you are
measuring a floating source, reference the input to ground.
You can ground reference a floating signal for each channel by using the
switch settings shown in Table 1. Refer to Figure 2 for switch locations.
Each channel has one switch with two positions as follows:
•
Floating signal sources—Use position F. Setting one of these
switches to position F connects a 100 kΩ resistor between the negative
input screw terminal for the channel and analog ground. This resistor
provides the necessary reference to ground for the channel.
•
Ground-referenced sources—Use position G. Setting the switch to
position G disconnects the resistor from the signal path.
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SCXI-1304 Terminal Block Installation Guide
Table 1. Floating and Ground-Referenced Signal Configuration
Switch Position
F
Description
Use this setting to provide a reference to ground for
floating signals.
G
F
Use this setting for signals that are already ground
referenced (factory setting).
G
Configuring AC/DC Coupling
You can configure each channel for either AC or DC coupling using the
switch settings shown in Table 2. Refer to Figure 2 for switch locations.
Each channel requires two switches that must be in the same position for
the coupling circuitry to properly operate. Configure the channels as
follows:
•
AC coupling—Set both switches to the AC position. This position
places single-pole highpass filters in the paths of both the positive and
negative channel inputs. Each filter consists of a 1 µF DC blocking
capacitor and a 1 MΩ resistor to analog ground, giving a –3 dB cutoff
frequency of 0.16 Hz. The capacitors can block up to 50 VDC.
•
DC coupling—Set both switches to the DC position. DC coupling
removes the filters from the signal paths and connects the screw
terminals directly to the module inputs.
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Table 2. AC/DC Coupling Configuration
Switch Position
AC
Description
Use this setting to AC couple the input signal.
DC
AC
Use this setting to DC couple the input signal
(factory setting).
DC
Connecting the Signals
When connecting the signals to the SCXI-1304, follow the labeling on the
SCXI-1304 for the appropriate module, as indicated in Figure 2.
To connect the signal to the terminal block, complete the following steps,
referring to Figures 1 and 2 as necessary:
1.
Unscrew the top cover screws and remove the cover.
2.
Configure each of the AC/DC coupling and ground-referencing
switches, depending on the signal you are measuring. The top set of
switches (S1, S2, and S3) corresponds to input channel 0, the next set
down (S4, S5, and S6) corresponds to input channel 1, and so on. The
bottom set of switches (S22, S23, and S24) corresponds to input
channel 7. Refer to Figure 2 for the switch locations.
3.
Loosen the strain-relief screws and remove the strain-relief bar.
4.
Run the signal wires through the strain-relief opening. You can add
insulation or padding if necessary.
5.
Prepare the signal wire by stripping the insulation no more than 7 mm
(0.28 in.).
6.
Connect the wires to the screw terminals by fully inserting the stripped
end of the wire into the terminal. No bare wire should extend past the
screw terminal. Exposed wire increases the risk of shorting and
causing a failure.
7.
Tighten the screw terminal to a torque of 0.57 to 0.79 N ⋅ m
(5–7 lb.-in.).
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SCXI-1304 Terminal Block Installation Guide
8.
Connect the shield or earth ground to the earth-ground lug.
9.
Reinstall the strain-relief bar and tighten the strain-relief screws.
10. Reinstall the top cover and tighten the top cover screws.
11. Connect the terminal block to the module front connector as explained
in the Installing the Terminal Block section.
2
6
7
3
1
4
5
Back View
1
2
3
4
Front View
Strain Relief Bar
Strain Relief Screws
Earth Ground Lug
Mating Connector
5
6
7
Thumbscrew
Top Cover Screws
Top Cover
Figure 1. SCXI-1304 Parts Locator Diagram
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1
2
3
4
5
6
7
8
9
10
11
12
1
2
3
4
Channel 0 Switches
Channel 1 Switches
Channel 2 Switches
Channel 3 Switches
5
6
7
8
Channel 4 Switches
Channel 5 Switches
Channel 6 Switches
Channel 7 Switches
9
10
11
12
Serial Number
Eight AC/DC Coupling Switches
Eight Floating/Ground-Reference Switches
Screw Terminals
Figure 2. SCXI-1304 Terminal Block Parts Locator Diagram
Installing the Terminal Block
To connect the terminal block to the SCXI module front connector,
complete the following steps:
1.
Connect the module front connector to its mating connector on the
terminal block.
2.
Tighten the top and bottom thumbscrews on the back of the terminal
block to hold it securely in place.
Specifications
All specifications are typical at 25 °C unless otherwise specified.
Analog Input
Input coupling ........................................ AC (1-pole highpass filter)
–3 dB cutoff frequency ................... 0.16 Hz1
1
The capacitors can block up to 50 VDC.
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SCXI-1304 Terminal Block Installation Guide
Maximum Working Voltage
Maximum working voltage refers to the signal voltage plus the
common-mode voltage.
Channel-to-earth .....................................60 V, Installation Category I
Channel-to-channel.................................60 V, Installation Category I
Note The maximum working voltage of non-isolated modules is found in the
specifications of the module.
Environmental
Operating temperature ............................0 to 50 °C
Storage temperature ................................–20 to 70 °C
Humidity .................................................10 to 90% RH, noncondensing
Maximum altitude...................................2,000 m
Pollution Degree (indoor use only) ........2
Safety
The SCXI-1304 is designed to meet the requirements of the following
standards of safety for electrical equipment for measurement, control, and
laboratory use:
•
IEC 61010-1, EN 61010-1
•
UL 3111-1, UL 61010B-1
•
CAN/CSA C22.2 No. 1010.1
Note For UL and other safety certifications refer to the product label or to ni.com.
Electromagnetic Compatibility
Emissions................................................EN 55011 Class A at 10 meters.
FCC Part 15A above 1 GHz
Immunity ................................................EN 61326:1997 + A21:2001,
Table 1
EMC/EMI ...............................................CE, C-Tick and FCC Part 15
(Class A) Compliant
Note For EMC compliance, operate this device with shielded cabling.
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CE Compliance
The SCXI-1304 meets the essential requirements of applicable European
Directives, as amended for CE Marking, as follows:
Low-Voltage Directive (safety) ............. 73/23/EEC
Electromagnetic Compatibility
Directive (EMC) .................................... 89/336/EEC
Note Refer to the Declaration of Conformity (DoC) for this product for any additional
regulatory compliance information. To obtain the DoC for this product, click Declarations
of Conformity Information at ni.com/hardref.nsf/.
Circuit Diagram
You do not need to read this section to operate the SCXI-1304. The circuit
diagram in Figure 3 is optional information that you can use if you want
more details about the SCXI-1304 circuitry. Figure 3 shows the circuitry
for one of the eight analog channels.
AC/DC
Coupling
Switch
DC
+
+
AC
1 µF,
10%,
50 V
Screw
Terminal
Inputs
1 MΩ
1%
AC/DC
Coupling
Switch
DC
–
Floating/
Ground-Referenced
Switch
Module
Inputs
–
AC
G
F
10 kΩ
5%
1 µF,
10%,
50 V
1 MΩ
1%
Figure 3. SCXI-1304 Circuit Diagram
© National Instruments Corporation
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SCXI-1304 Terminal Block Installation Guide