National Instruments SCXI-1338 User manual

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National Instruments™,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.
322204B-01 ©Copyright 1998, 2000 National Instruments Corp. All rights reserved. December 2000
INSTALLATION GUIDE
SCXI -1338 CURRENT INPUT,H
IGH-VOLTAGE
TERMINAL BLOCK
This guide describes how to install and use the SCXI-1338 terminal block
with your SCXI-1120, SCXI-1120D, SCXI-1125, or SCXI-1126 module.
Introduction
The SCXI-1338 current input terminal block is a shielded terminal block
with screw terminals that connect to the SCXI-1120, SCXI-1120D,
SCXI-1125, and SCXI-1126 modules. The SCXI-1338 has eight 249 Ω
precision resistors to convert current to voltage when measuring 0–20 mA
and 4–20 mA process current sources.
The terminal block has 18 screw terminals for easy connection. Eight pairs
of screw terminals are for signal connection to the eight module inputs. One
pair of terminals connects to the SCXI chassis ground.
What You Need to Get Started
To set up and use your SCXI-1338 terminal block, you need the following
items:
❑SCXI-1338 current input terminal block
❑SCXI-1338 Current Input, High-Voltage Terminal Block
Installation Guide
❑SCXI chassis
❑One of the following modules:
– SCXI-1120
– SCXI-1120D
– SCXI-1125
– SCXI-1126
™
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SCXI-1338 Installation Guide 2 ni.com
❑Number 1 and 2 Phillips-head screwdrivers
❑1/8 in. flathead screwdriver
❑Long-nose pliers
❑Wire cutter
❑Wire insulation stripper
Conventions
The following conventions are used in this guide:
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.
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.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames and extensions, and code excerpts.
Safety Information
Caution Do not operate the device in an explosive atmosphere or where there may be
flammable gases or fumes.
Keep away from live circuits. Do not remove equipment covers or shields unless you are
trained to do so. If signal wires are connected to the device, hazardous voltages can exist
even when the equipment is turned off. To avoid a shock hazard, do not perform procedures
involving cover or shield removal unless you are qualified to do so and disconnect all field
power prior to removing covers or shields.
Equipment described in this document must be used in an Installation Category II1
environment per IEC 60664-1. This category requires local level supply mains-connected
installation.
1Category II refers to local-level power distribution, such as that provided by a standard wall outlet.
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©National Instruments Corporation 3 SCXI-1338 Installation Guide
Do not operate damaged equipment. The safety protection features built into this device
can become impaired if the device becomes damaged in any way. If the device is damaged,
turn the device off and do not use it until service-trained personnel can check its safety.
If necessary, return the device to National Instruments for service and repair to ensure that
its safety is not compromised.
Do not operate this equipment in a manner that contradicts the information specified in this
document. Misuse of this equipment could result in a shock hazard.
Do not substitute parts or modify equipment. Because of the danger of introducing
additional hazards, do not install unauthorized parts or modify the device. Return the
device to National Instruments for service and repair to ensure that its safety features are
not compromised.
Yo u must insulate all of your signal connections to the highest voltage with which the
SCXI-1338 can come in contact.
When using the device with high common-mode voltages, you must insulate your signal
wires for the highest input voltage. National Instruments is not liable for any damages or
injuries resulting from inadequate signal wire insulation. Use only 26-14 AWG wire with
a minimum voltage rating of 300 V and a temperature value of 60 °C for measuring up
to 300 V.
When connecting or disconnecting signal lines to the SCXI terminal block screw terminals,
make sure the lines are powered off. Potential differences between the lines and the SCXI
ground can create a shock hazard while you connect the lines.
Connections, including power signals to ground and vice versa, that exceed any of the
maximum signal ratings on the SCXI device can create a shock or fire hazard, or can
damage any or all of the boards connected to the SCXI chassis, the host computer, and the
SCXI device. National Instruments is not liable for any damages or injuries resulting from
incorrect signal connections.
If hazardous voltages (≥30 Vrms and42.4V
peak or 60 VDC) are present, you must connect
a safety earth-ground wire to the terminal block safety-ground lug, shown in Figure 2. This
complies with safety agency requirements and protects against electric shock when the
terminal block is not connected to the chassis. To connect the safety earth-ground to the
safety-ground lug, run an earth-ground wire from the signal source to the terminal block.
National Instruments is not liable for any damages or injuries resulting from inadequate
safety earth-ground connections.
Do not loosen or re-orient the safety-ground lug hardware when connecting the
safety-ground wire; to do so reduces the safety isolation between the high voltage and
safety ground.
Clean the module and accessories by brushing off light dust with a soft non-metallic brush.
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SCXI-1338 Installation Guide 4 ni.com
Remove other contaminants with a stiff non-metallic brush. The unit must be completely
dry and free from contaminants before returning it to service.
The terminal block must be used with a UL-listed SCXI chassis.
Current-Loop Resistors
Note Refer to the Safety Information and Connecting the Signals sections before
removing equipment covers or connecting or disconnecting any signal wires.
The SCXI-1338 is used with the SCXI-1120, SCXI-1120D, SCXI-1125,
and SCXI-1126 modules to measure 0–20 mA and 4–20 mA sources. The
SCXI-1338 contains a precision 249 Ω,0.1%,10ppm,1/4Wresistor
across each channel to convert current to voltage. The SCXI module then
measures the voltage and the data acquisition (DAQ) device acquires
the voltage.
To convert the voltage read by the SCXI module to the actual current being
measured, use the following formula:
current = measured voltage / 249
The voltage measured for a 4–20 mA current source is in the range of
0.996–4.98 VDC.
The SCXI-1338 can measure both current sources and voltage sources.
When measuring voltage signals, you must remove the current-loop resistor
for that input channel. You can identify the resistor for a particular channel
by its reference designator. The reference designator matches the channel
the resistor is across. For example, input channel 0 has resistor R0 across it.
Input channel 7 has resistor R7 across it. Figure 1 shows the SCXI-1338
signal connections.
Figure 1. SCXI-1338 Signal Connections
1 Product Name, Assembly Number,
Revision Letter, and Serial Number
2 Channel Labeling
3 Current-Loop Resistors
2
3
1
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©National Instruments Corporation 5 SCXI-1338 Installation Guide
Connecting the Signals
Note Refer to the Safety Information section before removing equipment covers or
connecting or disconnecting any signal wires.
When connecting your signals to the SCXI-1338, follow the labeling on the
SCXI-1338 for the appropriate module, as indicated in Figure 1.
To connect the signal to the terminal block, perform the following steps,
referringtoFigures1and2asnecessary:
1. Unscrew the top cover screws and remove the top cover.
2. Loosen the strain-relief screws and remove the strain-relief bar.
3. Run the signal wires through the strain-relief opening. You can add
insulation or padding, if necessary.
4. Prepare your signal wire by stripping the insulation no more
than 7 mm.
5. Connect the wires to the screw terminals by inserting the stripped end
of the wire fully into the terminal. No bare wire should extend past the
screw terminal. Exposed wire increases the risk of a short circuit and
equipment failure.
6. Tighten the screws to a torque of 5–7in.-lb.
7. Connect safety earth ground to the safety ground lug. Refer to the
Safety Information section for connection information.
8. Reinstall the strain-relief bar and tighten the strain-relief screws.
9. Reinstall the top cover and tighten the top cover screws.
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SCXI-1338 Installation Guide 6 ni.com
Figure 2. SCXI-1338 Parts Locator Diagram
Installing the Terminal Block
To connect the terminal block to the SCXI module front connector, perform
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.
1 Strain-Relief Bar
2 Strain-Relief Screws
3 Safety Ground Lug
4 Mating Connector
5 Thumbscrew
6 Top Cover Screws
7TopCover
3
4
2
1
5
6
7
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©National Instruments Corporation 7 SCXI-1338 Installation Guide
Specifications
All specifications are typical at 25 °C unless otherwise specified.
Electrical
Compatible modules
SCXI-1120/D .................................. 8 input channels
SCXI-1125 ...................................... 8 input channels
SCXI-1126 ...................................... 8 input channels
Coupling................................................. DC1
Current-receiver resistors
Resistor provided ............................ 1 per channel, socketed
(8 total)
Resistance ....................................... 249 Ω
Resistance accuracy ........................ ±0.1%
Temperature coefficient.................. 10 ppm/°C
Wattage ........................................... 0.25 W
Maximum working voltage
(signal + common –mode)
Channel to ground........................... Each channel must remain within
300 Vrms or ±300 VDC of ground
Channel to channel.......................... Each channel must remain within
300 Vrms or ±300 VDC of the
voltage applied to any other
channel
Maximum input current ......................... ±20 mA
Field-wiring connectivity
Screw terminals for signals............. 16 (8 pairs)
Screw terminals
for functional earth ground ............. 2
Safety earth-ground lugs................. 1
Strain relief ..................................... Strain-relief bar at
terminal block entrance
Maximum wire gauge ..................... 16 AWG
1In instrumentation terminology, DC coupling means that both DC and AC signals are passed.
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SCXI-1338 Installation Guide 8 ni.com
Terminal spacing .............................0.5 cm (0.2 in.)
center-to-center
Dimensions of front entrance ..........1.2 by 7.3 cm
(0.47by2.87in.)
Solder pads for
additional components.....................none
Mechanical
Dimensions .............................................17.8 by 7.94 by 3.0 cm
(7.0 by 3.125 by 1.2 in.)
Weight ....................................................200 gm
(7 oz.)
Environmental
Operating temperature ............................0 to 50 °C
Storage temperature ................................–20 to 70 °C
Relative humidity ...................................10 to 90% noncondensing
Pollution degree......................................2
Altitude (maximum) ...............................2000 m
Safety
Designed in accordance with IEC 61010-1, UL 3111-1, and CAN/CSA
C22.2 No. 1010.1 for electrical measuring and test equipment.
Installation Category II
Pollution degree 2
Electromagnetic Compatibility
EMC/EMI ...............................................CE, C-Tick and FCC Part 15
(Class A) Compliant
Electrical emissions ................................EN 55011 Class A at 10 m,
FCC Part 15A above 1 GHz
Electrical immunity ................................Evaluated to EN 61326:1998,
Table 1
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©National Instruments Corporation 9 SCXI-1338 Installation Guide
Note This device should only be operated with shielded cabling for full EMC and EMI
compliance. See the Declaration of Conformity for this product for any additional
regulatory compliance information.
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