SCXI-1322 High-Voltage Terminal Block Installation Guide

INSTALLATION GUIDE
SCXI™-1322 HIGH-VOLTAGE TERMINAL BLOCK
This guide describes how to use and install the SCXI-1322 terminal block
with the SCXI-1122 module.
Introduction
The SCXI-1322 terminal block consists of a shielded board with 48 screw
terminals for easy connection to the SCXI-1122 input connector. Sixteen
pairs of screw terminals connect to the SCXI-1122 module inputs. The
remaining seven pairs of screw terminals are for the module excitation
channels.
What You Need to Get Started
To set up and use your SCXI-1322 terminal block, you need the following
items:
❑ SCXI-1322 terminal block
❑ SCXI-1322 High-Voltage Terminal Block Installation Guide
❑ SCXI chassis
❑ SCXI-1122 module
❑ Number 1 and 2 Phillips-head screwdrivers
❑ 1/8 in. flathead screwdriver
❑ Long-nose pliers
❑ Wire cutter
❑ Wire insulation stripper
CVI™, LabVIEW™, and National Instruments™, ni.com™, NI-DAQ™, and SCXI™ are trademarks of National Instruments Corporation. Product and
company names are trademarks or trade names of their respective companies.
321925B-01
© Copyright 1993, 1999 National Instruments Corp. All rights reserved.
November 1999
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
Cautions 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 may 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 II
environment per IEC 664. This category requires local level supply mains-connected
installation.
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 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.
Terminals are for use only with equipment that has no accessible live parts.
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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.
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 voltage rating of 300 V and 60 °C for signals that may come in contact with 250 V;
use only 600 V and 60 °C wire for signals that may come in contact with 480 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 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 high voltages (≥30 Vrms and 42.4 Vpeak or 60 VDC) are present, you must connect a safety
earth ground wire to the terminal block safety ground solder lug, shown in Figure 1. 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 solder lug, run an earth ground wire in the cable 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 solder lug hardware when connecting the
safety ground wire; to do so reduces the safety isolation between the high voltage and
safety ground.
Using the VEX/SENSE+ and the VEX/SENSE– Terminals
for Strain-Gauge Excitation
Your terminal block has two terminals labeled VEX/SENSE+ and
VEX/SENSE–. When resistors R3 and R4 are loaded (factory default), you
can use the VEX/SENSE+ and VEX/SENSE– terminals as VEX+ and
VEX– terminals, respectively. When you have a heavy load—for example,
all 16 channels are connected to 16 120 Ω strain-gauge half-bridges—you
should remove resistors R3 and R4 to transform the VEX/SENSE+ and
VEX/SENSE– terminals to sense terminals. These terminals must connect
to the VEX+ and VEX– leads at the load for remote sensing and therefore
compensate for the voltage drop in the excitation leads.
© National Instruments Corporation
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SCXI-1322 Installation Guide
It is important to notice that because the SCXI-1122 provides a single
voltage excitation channel, you can remotely sense your excitation voltage
at a single load location. Therefore, when using multiple loads, you either
have to sense in the terminal block (leave R3 and R4 in place) or make sure
your loads are located close to each other and remotely sense at the end of
the excitation leads. Use a single pair of excitation leads for all the loads,
as shown in Figure 1.
Use short lengths of large-gauge
wire to minimize the voltage
drop in each lead.
SENSE +
VEX +
120 Ω
CH+(0)
120 Ω
120 Ω
120 Ω
CH+(1)
CH+(15)
120 Ω
120 Ω
VEX –
SENSE –
Figure 1. Remote Sensing with Multiple Loads
Figure 2 shows a setup where remote sensing is not used. In this case, use
a different pair of excitation leads for each load. To minimize the voltage
drop in each pair of excitation leads, use large gauge wires to reduce the
I * RLEAD drop.
VEX +
VEX –
I
120 Ω
120 Ω
CH+(0)
120 Ω
I=
120 Ω
CH+(1)
CH+(15)
120 Ω
3.333 V
240+ 2R LEAD
2R LEAD<< 240Ω
120 Ω
R LEAD
Figure 2. No Remote Sensing
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Figure 3 shows multiple loads with bad remote sensing. Only the load at
which the sense leads connect are correctly regulated. The other loads
suffer from the voltage drop in their excitation leads because of current
flow.
Long Wire
VEX +
120 Ω
s
on
ti
ec
n
on
dC
Ba
CH+(0)
120 Ω
120 Ω
CH+(1)
CH+(2)
120 Ω
120 Ω
VEX –
SENSE +
120 Ω
SENSE –
s
on
ti
ec
n
on
C
ad
B
120 Ω
CH+(6)
120 Ω
120 Ω
120 Ω
CH+(10)
CH+(3)
120 Ω
120 Ω
Figure 3. Multiple Loads with Bad Remote Sensing
© National Instruments Corporation
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SCXI-1322 Installation Guide
Temperature Sensor Output and Accuracy
The SCXI-1322 temperature sensor outputs 1.91 to 0.58 V from 0 to 55 °C
and has an accuracy of ±0.5 °C over the 15 to 35 °C range and ±0.9 °C over
the 0 to 15 °C and 35 to 55 °C ranges.1
National Instruments software can convert a thermistor voltage to the
thermistor temperature for the circuit diagram shown later in this guide.
In LabVIEW, you can use the ConvertThermistorReading VI in the
Data Acquisition»Signal Conditioning palette. If you are using
LabWindows/CVI or NI-DAQ, use the Thermistor_Convert function.
The VI takes the output voltage of the temperature sensor, the reference
voltage, and the precision resistance and returns the thermistor temperature.
Alternatively, you can use the following formulas:
T(° C) = TK – 273.15
where TK is the temperature in Kelvin
1
T K = ------------------------------------------------------------3
[ a + b ( ln R T ) + c ( ln R T ) ]
a = 1.295361 × 10 – 3
b = 2.343159 × 10 – 4
c = 1.018703 × 10 – 7
RT = resistance of the thermistor in ohms
V TEMPOUT
R T = 5, 000  --------------------------------------
 2.5 – V TEMPOUT
VTEMPOUT = output voltage of the temperature sensor
[T(°C ) ]9
T ( °F ) = ----------------------- + 3
5
where T(°F) and T(°C) are the temperature readings in degrees Fahrenheit
and degrees Celsius, respectively.
Note Use an average of a large number of samples to obtain the most accurate reading.
Noisy environments require more samples for greater accuracy.
1
Includes the combined effects of the temperature sensor accuracy and the temperature difference between the temperature
sensor and any screw terminal. The temperature sensor accuracy includes tolerances in all component values, the effects
caused by temperature and loading, and self-heating.
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Signal Connection
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-1322, follow the labeling on the
SCXI-1322 for the appropriate module, as indicated in Figure 5.
To connect the signal to the terminal block, perform the following steps,
referring to Figures 4 and 5 as necessary:
1.
Unscrew the top cover screws and remove the 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 shorting and
causing a failure.
6.
Tighten the screws to a torque of 5–7 in.-lb.
7.
Connect safety earth ground to the safety-ground solder 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.
10. Connect the terminal block to the module front connector as explained
in the Installation section.
© National Instruments Corporation
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SCXI-1322 Installation Guide
Figure 4 shows the SCXI-1322 terminal block parts locator diagram.
2
6
7
3
1
4
5
Back View
1
2
Strain-Relief Bar
Strain-Relief Screws
3
Front View
Safety-Ground
Solder Lug
4
5
Mating Connector
Thumbscrew
6
7
Top Cover Screws
Top Cover
Figure 4. SCXI-1322 Parts Locator Diagram
Figure 5 shows the SCXI-1322 signal connections.
4
5
6
3
2
2
1
1
2
Solder Lugs
Screw Terminals
3
4
Product Name, Assembly Number, and Revision Letter 5
R3
6
R4
Serial Number
Figure 5. SCXI-1322 Signal Connections
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Installation
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.
Note For accurate cold-junction compensation, place the SCXI chassis away from an
extreme temperature differential.
Cleaning the Terminal Block
Clean the terminal block by brushing off light dust with a soft, nonmetallic
brush. Remove other contaminants with deionized water and a stiff
nonmetallic brush. The unit must be completely dry and free from
contaminants before returning to service.
Specifications
All specifications are typical at 25 °C unless otherwise specified.
Cold-junction sensor
Accuracy1 ........................................ 0.65° from 15 to 35 °C
0.85° from 0 to 15 °C and
35 to 55 °C
Repeatability ................................... 0.4° from 15 to 35 °C
Output ............................................. 1.91 to 0.58 V from 0 to 55 °C
Common-mode isolation
Terminal to terminal ....................... 250 Vrms
Terminal to earth............................. 480 Vrms
1
The temperature sensor accuracy includes tolerances in all component values, effects caused by temperature, loading,
self-heating, and temperature gradients.
© National Instruments Corporation
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SCXI-1322 Installation Guide
Environment
Operating temperature ............................0 to 50 °C
Storage temperature ................................–20 to 70 °C
Relative humidity ...................................5% to 90% noncondensing
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.
Approved at altitudes up to 2000 meters.
Installation Category II
Pollution Degree 2
Temperature Sensor Circuit Diagram
The circuit diagram in Figure 6 is optional information that you can use if
you want more details about the SCXI-1322 temperature sensor.
+5 V
4.7 kΩ
1%
2.5 V
LM 4040
2.5 V
0.1%
2
5 kΩ
0.1%
0.1 µF
-t o
MTEMP
+ 1 10 µF
5 kΩ
at 25o C 2 16 V
1
2
0.1 µF
Figure 6. Temperature Sensor Circuit Diagram
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Technical Support Resources
NI Web Support
To provide you with immediate answers and solutions 24 hours a day,
365 days a year, National Instruments maintains extensive online technical
support resources. They are available to you at no cost, are updated daily,
and can be found in the Technical Support section of our Web site at
www.ni.com/support
Worldwide Support
National Instruments has offices located around the globe. Many branch
offices maintain a Web site to provide information on local services. You
can access these Web sites from www.ni.com/worldwide
For telephone support in the United States, dial 512 795 8248. For
telephone support outside the United States, contact your local branch
office:
Australia 03 9879 5166, Austria 0662 45 79 90 0, Belgium 02 757 00 20,
Brazil 011 284 5011, Canada (Calgary) 403 274 9391,
Canada (Ontario) 905 785 0085, Canada (Québec) 514 694 8521,
China 0755 3904939, Denmark 45 76 26 00, Finland 09 725 725 11,
France 01 48 14 24 24, Germany 089 741 31 30, Greece 30 1 42 96 427,
Hong Kong 2645 3186, India 91805275406, Israel 03 6120092,
Italy 02 413091, Japan 03 5472 2970, Korea 02 596 7456,
Mexico (D.F.) 5 280 7625, Mexico (Monterrey) 8 357 7695,
Netherlands 0348 433466, Norway 32 27 73 00, Poland 48 22 528 94 06,
Portugal 351 1 726 9011, Singapore 2265886, Spain 91 640 0085,
Sweden 08 587 895 00, Switzerland 056 200 51 51,
Taiwan 02 2377 1200, United Kingdom 01635 523545
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SCXI-1322 Installation Guide