Allen-Bradley 1746-NT8 User manual

SLC 500
Thermocouple/mV
Analog Input
Module
1746-NT8
User Manual

Important User Information
Solid state equipment has operational characteristics differing from those of
electromechanical equipment. Safety Guidelines for the Application,
Installation and Maintenance of Solid State Controls (Publication SGI-1.1
available from your local Rockwell Automation sales office or online at
http://www.ab.com/manuals/gi) describes some important differences
between solid state equipment and hard-wired electromechanical devices.
Because of this difference, and also because of the wide variety of uses for
solid state equipment, all persons responsible for applying this equipment
must satisfy themselves that each intended application of this equipment is
acceptable.
In no event will Rockwell Automation, Inc. be responsible or liable for
indirect or consequential damages resulting from the use or application of
this equipment.
The examples and diagrams in this manual are included solely for illustrative
purposes. Because of the many variables and requirements associated with
any particular installation, Rockwell Automation, Inc. cannot assume
responsibility or liability for actual use based on the examples and diagrams.
No patent liability is assumed by Rockwell Automation, Inc. with respect to
use of information, circuits, equipment, or software described in this manual.
Reproduction of the contents of this manual, in whole or in part, without
written permission of Rockwell Automation, Inc. is prohibited.
Throughout this manual, when necessary we use notes to make you aware of
safety considerations.
WARNING Identifies information about practices or circumstances
that can cause an explosion in a hazardous environment,
which may lead to personal injury or death, property
damage, or economic loss.
IMPORTANT Identifies information that is critical for successful
application and understanding of the product.
ATTENTION Identifies information about practices or circumstances
that can lead to personal injury or death, property
damage, or economic loss. Attentions help you:
•identify a hazard
•avoid a hazard
•recognize the consequence
SHOCK HAZARD Labels may be located on or inside the equipment (e.g.,
drive or motor) to alert people that dangerous voltage may
be present.
BURN HAZARD Labels may be located on or inside the equipment (e.g.,
drive or motor) to alert people that surfaces may be
dangerous temperatures.

iPublication 1746-UM022B-EN-P - January 2005
Table of Contents
Preface Who Should Use This Manual . . . . . . . . . . . . . . . . . . . . . . P-1
What This Manual Covers . . . . . . . . . . . . . . . . . . . . . . . . . P-1
Related Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . P-2
Common Techniques Used in this Manual . . . . . . . . . . . . . P-2
Chapter 1
Module Overview
General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Input Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Hardware Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Diagnostic LEDs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
System Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Module Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Module Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Block Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Linear Millivolt Device Compatibility. . . . . . . . . . . . . . . 1-7
Chapter 2
Installing And Wiring Your
Module
Electrostatic Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Considerations for a Modular System . . . . . . . . . . . . . . 2-2
Fixed I/O Chassis - I/O Module Compatibility . . . . . . . . 2-3
General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Module Installation and Removal . . . . . . . . . . . . . . . . . . . . 2-5
Terminal Block Removal . . . . . . . . . . . . . . . . . . . . . . . 2-6
Wiring Your Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Preparing and Wiring the Cables . . . . . . . . . . . . . . . . . 2-9
Cold-Junction Compensation (CJC) . . . . . . . . . . . . . . . . 2-11
Chapter 3
Considerations Before Using Your
Module
Module ID Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Module Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Output Image - Configuration Words . . . . . . . . . . . . . . 3-2
Input Image - Data Words and Status Words. . . . . . . . . 3-3
Channel Filter Frequency Selection . . . . . . . . . . . . . . . . . . 3-3
Channel Cut-Off Frequencyc . . . . . . . . . . . . . . . . . . . . 3-4
Channel Step Response . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Update Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Update Time Calculation Example . . . . . . . . . . . . . . . . 3-8
Channel Turn-On, Turn-Off, and Reconfiguration Times . . . 3-8
Auto-calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Response to Slot Disabling . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Input Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Output Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

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Table of Contents ii
Chapter 4
Channel Configuration, Data, and
Status
Channel Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Channel Configuration Procedure . . . . . . . . . . . . . . . . . . . 4-2
Select Channel Enable (Bit 0) . . . . . . . . . . . . . . . . . . . . 4-5
Select Input Types (Bits 1 through 4) . . . . . . . . . . . . . . 4-5
Select Data Format (Bits 5 and 6) . . . . . . . . . . . . . . . . . 4-5
Using Scaled-for-PID and Proportional Counts . . . . . . . 4-6
Effective Resolutions . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Scaling Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Select Open-Circuit State (Bits 7 and 8). . . . . . . . . . . . . 4-9
Select Temperature Units (Bit 9) . . . . . . . . . . . . . . . . . . 4-10
Select Channel Filter Frequency (Bits 10 and 11) . . . . . . 4-10
Unused Bits (Bits 12 through 14) . . . . . . . . . . . . . . . . . 4-11
Select Input Image Type (Bit 15) . . . . . . . . . . . . . . . . . 4-11
Channel Data/Status Word. . . . . . . . . . . . . . . . . . . . . . . . . 4-11
Channel Status Checking . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Channel Status (Bit 0) . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Input Type Status (Bits 1 through 4) . . . . . . . . . . . . . . . 4-14
Data Format Type Status (Bits 5 and 6) . . . . . . . . . . . . . 4-14
Open-Circuit Type Status (Bits 7 and 8) . . . . . . . . . . . . 4-14
Temperature Units Type Status (Bit 9). . . . . . . . . . . . . . 4-14
Channel Filter Frequency (Bits 10 and 11). . . . . . . . . . . 4-15
Open-Circuit E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15
Under-Range Error (Bit 13). . . . . . . . . . . . . . . . . . . . . . 4-15
Over-Range Error (Bit 14). . . . . . . . . . . . . . . . . . . . . . . 4-15
Channel Error (Bit 15) . . . . . . . . . . . . . . . . . . . . . . . . . 4-15
Chapter 5
Programming Examples
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
Automatic Monitoring Thermocouples and CJC Sensors . . . 5-3
Verifying Configuration Changes . . . . . . . . . . . . . . . . . . . . 5-3
Interfacing to the PID Instruction. . . . . . . . . . . . . . . . . . . . 5-7
Monitoring Channel Status Bits . . . . . . . . . . . . . . . . . . . . . 5-8
Monitoring Channel Status Bits Example . . . . . . . . . . . . 5-9
PLC 5 Example with NT8 in Remote I/O Rack . . . . . . . . . . 5-13
SLC 500 Example with NT8 in Remote I/O Rack. . . . . . . . . 5-15
Chapter 6
Troubleshooting Your Module
Module and Channel Diagnostics. . . . . . . . . . . . . . . . . . . . 6-1
Module Diagnostics at Powerup . . . . . . . . . . . . . . . . . . 6-1
Channel Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
LED Troubleshooting Tables. . . . . . . . . . . . . . . . . . . . . 6-3
Channel-status LEDs (Green) . . . . . . . . . . . . . . . . . . . . 6-4
Open-circuit Detection (Bit 12). . . . . . . . . . . . . . . . . . . 6-4

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Table of Contents iii
Out-of-Range Detection (Bit 13 for Under Range, Bit 14 for
Over Range) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
Channel Error (Bit 15) . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
Module Status LED (Green) . . . . . . . . . . . . . . . . . . . . . 6-5
Interpreting I/O Error Codes . . . . . . . . . . . . . . . . . . . . . . . 6-5
Chapter 7
Maintaining Your Module And
Safety Considerations
Preventive Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Appendix A
Module Specifications
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Physical Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2
Environmental Specifications . . . . . . . . . . . . . . . . . . . . . . . A-2
Input Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3
Overall Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
Millivolt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
Thermocouple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6
Appendix B
Using Grounded Junction,
Ungrounded Junction, and
Exposed Junction Thermocouples
Thermocouple Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
Grounded Junction . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Ungrounded (Insulated) Junction . . . . . . . . . . . . . . . . . B-2
Exposed Junction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Grounded Junction . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3
Exposed Junction Thermocouples. . . . . . . . . . . . . . . . . B-4
Appendix C
Configuring the 1746-NT8 Module
with RSLogix 500
Glossary
Index

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Table of Contents iv

1Publication 1746-UM022B-EN-P - January 2005
Summary of Changes
The information below summarizes the changes to this manual since
the last printing. Updates to the manual include using RSLogix 500
instead of APS software.
To help you find new and updated information in this release of the
manual, we have included change bars as shown to the right of this
paragraph.
The table below lists the sections that document new features and
additional or updated information on existing features.
For this information: See
updated data table for initial programming page 5-2
added SLC 500 example with NT8 in
Remote I/O Rack
page 5-15
updated thermocouple graphs page A-8
configuring NT8 with RSLogix 500 page C-1

Publication 1746-UM022B-EN-P - January 2005
Summary of Changes 2

1Publication 1746-UM022B-EN-P - January 2005
Preface
Read this preface to familiarize yourself with this user manual. This
preface covers:
•who should use this manual
•what this manual provides
•related documents
•common techniques used in this manual
Who Should Use This
Manual
Use this manual if you design, install, program, or maintain a control
system that uses SLC 500controllers.
You should have a basic understanding of SLC 500 products. You
should also understand electronic process control and the ladder
program instructions required to generate the electronic signals that
control your application. If you do not, contact your local Rockwell
Automation representative for the proper training before using these
products.
What This Manual Covers
This manual covers the 1746-NT8 thermocouple/millivolt analog input
module. It contains the information you need to install, wire, use, and
maintain these modules. It also provides diagnostic and
troubleshooting help should the need arise.

Publication 1746-UM022B-EN-P - January 2005
Preface 2
Related Documentation
The following table lists several Rockwell Automation documents that
may help you as you use these products.
If you would like to:
•view and download the publication, go to Literature Library at
http://www.rockwellautomation.com/literature
•order printed copies, contact your Allen-Bradley Distributor or
Rockwell Automation Sales Office.
Common Techniques Used
in this Manual
The following conventions are used throughout this manual:
•Bulleted lists such as this one provide information, not
procedural steps.
•Numbered lists provide sequential steps or hierarchical
information.
•Text in this font indicates words or phrases you should type.
•Key names appear in bold, capital letters within brackets (for
example, [ENTER]).
Publication Number Title
1746-SG001 SLC 500™ Systems Selection Guide
SGI-1.1 Safety Guidlines for the Application, Installation and
Maintenance of Solid State Controllers
1770-4.1 Industrial Automation Wiringing and Grounding Guidelines
1747-UM011 SLC 500 Modular Modular Hardware Style User Manual
1747-6.21 Installation & Operation Manual for Fixed Hardware Style
Programmable Controllers
1747-RM001 SLC 500 Instruction Set Reference Manual
AG-7.1 Allen-Bradley Industrial Automation Glossary

1Publication 1746-UM022B-EN-P - January 2005
Chapter 1
Module Overview
This chapter describes the thermocouple/mV input module and
explains how the SLC 500 processor reads thermocouple or millivolt
analog input data from the module.
Read this chapter to familiarize yourself further with your
thermocouple/mV analog input module. This chapter covers:
•general description and hardware features
•an overview of system and module operation
•block diagram of channel input circuits
General Description
This module mounts into 1746 I/O chassis for use with SLC 500 fixed
and modular systems. The module stores digitally converted
thermocouple/mV analog data in its image table for retrieval by all
fixed and modular SLC 500 processors. The module supports
connections from any combination of up to eight thermocouple/mV
analog sensors.
Input Ranges
The following tables define thermocouple types and associated
temperature ranges and the millivolt analog input signal ranges that
each of the module’s input channels support. To determine the
practical temperature range of your thermocouple, refer to the
specifications in Appendix A.
Thermocouple Temperature Ranges
Type °C Temperature Range °F Temperature Range
J -210°C to +760°C -346°F to +1400°F
K -270°C to +1370°C -454°F to +2498°F
T -270°C to +400°C -454°F to +752°F
B +300°C to +1820°C +572°C to +3308°F
E -270°C to +1000°C -454°F to +1832°F
R 0°C to +1768°C +32 F to +3214°F

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1-2 Module Overview
Millivolt Input Ranges(1)
Each input channel is individually configured for a specific input
device, and provides open-circuit, over-range, and under-range
detection and indication.
Hardware Features
The module fits into any single slot for I/O modules in either an SLC
500 modular system or an SLC 500 fixed system expansion chassis
(1746-A2), except the zero slot which is reserved for the processor. It
is a Class 1 module using 8 input words and 8 output words.(2)
The module contains a removable terminal block providing
connections for eight thermocouple and/or analog input devices. On
the terminal block are two cold-junction compensation (CJC) sensors
that compensate for the cold junction at ambient temperature. It
should also be noted there are no output channels on the module.
Configure the module with software rather than with jumpers or
switches.
S 0°C to +1768°C +32°F to +3214°F
N 0°C to +1300°C +32°F to +2372°F
CJC Sensor -25°C to +105°C -13°F to +221 °F
-50 to +50 mV
-100 to +100 mV
(1) Output impedance of input device must be less than 100 ohm to meet accuracy specifications.
(2) Requires use of a Block Transfer when used in a remote rack with a 1747-ASB.
IMPORTANT There is a jumper (JP1) on the circuit board. The
module is shipped with the jumper in the up
position as illustrated below. Do not change the
position of JP1. The jumper is used for test purposes
only.
Type °C Temperature Range °F Temperature Range

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Module Overview 1-3
Hardware Features
Diagnostic LEDs
The module contains diagnostic LEDs that help you identify the
source of problems that may occur during power-up or during normal
operation. Power-up and channel diagnostics are explained in
Chapter 6, Testing Your Module.
System Overview
The module communicates with the SLC 500 processor and receives
+5V dc and +24V dc power from the system power supply through
the parallel backplane interface. No external power supply is
required. You may install as many thermocouple modules in the
system as the power supply can support.
Hardware Function
Channel Status LED Indicators Display operating and fault status of
channels 0 to 7
Module Status LED Displays operating and fault status of the
module
Side Label (Nameplate) Provides module information
Removable Terminal Block Provides electrical connection to input
devices
Door Label Permits easy terminal identification
Cable Tie Slots Secure and route wiring from module
Self Locking Tabs Secure module in chassis slot
SLC 500
CAT SERIAL NO.
THERMOCOUPLE/mV INPUT MODULE
MADE IN USAFAC 1M
INPUT SIGNAL RANGES
THERMOCOUPLE TYPES: VOL TAGE:
±100mVDC to +100mVDC
±50mVDC to +50mVDC
SER FRN
)ULLISTED IND. CONT . EQ.
FOR HAZ. LOC. A196
CLASS I, GROUPS A, B, C AND D, DIV .2
OPERA TING
)
SA J, K, T, E, R, S, B, N
TEMPERA TURE CODE T3C
1746 NT4 NT4±xxx x
MODULE
0
1
4
5
2
1
2
3
CHANNEL
STATUS
THERMOCOUPLE/mV
INPUT
CJC A+
CJC A-
CHL 0+
CHL 0-
SHIELD
CHL 1+
CHL 1-
CHL 2+
CHL 2-
SHIELD
CHL 3+
CHL 3-
CHL 4+
CHL 4-
SHIELD
CHL 5+
CHL 5-
CHL 6+
CHL 6-
SHIELD
CHL 7+
CHL 7-
CJC B+
CJC B-
1746-NT8
JP1
Channel Status
LEDs (green)
Module Status
LEDs (green)
Removable
Terminal Block
CJC Sensors
Cable Tie Slots
Door Label
Jumper - Do not move Self-Locking Tabs
Side Label

Publication 1746-UM022B-EN-P - January 2005
1-4 Module Overview
Each module channel can receive input signals from a thermocouple
or a mV analog input device. You configure each channel to accept
either one. When configured for thermocouple input types, the
module converts analog input voltages into cold-junction
compensated and linearized, digital temperature readings. The
module uses National Institute of Standards and Technology (NIST)
ITS-90 for thermocouple linearization.
When configured for millivolt analog inputs, the module converts
analog values directly into digital counts. The module assumes that
the mV input signal is linear.
System Operation
At power-up, the module checks its internal circuits, memory, and
basic functions. During this time the module status LED remains off. If
the module finds no faults, it turns on its module status LED.
After completing power-up checks, the module waits for valid channel
configuration data from your SLC ladder logic program (channel status
LEDs are off). After channel configuration data is transferred and
channel enable bits are set, the enabled channel status LEDs turn on.
Then the channel continuously converts the thermocouple or millivolt
input to a value within the range you selected for the channel.
Each time the module reads an input channel, the module tests that
data for a fault, i.e. over-range or under-range condition. If open
circuit detection is enabled, the module tests for an open-circuit
condition. If it detects an open-circuit, over-range, or under-range
condition, the module sets a unique bit in the channel status word
and causes the channel status LED to flash.
The SLC processor reads the converted thermocouple or millivolt data
from the module at the end of the program scan, or when
commanded by the ladder program. After the processor and module
determine that the data transfer was made without error, the data can
be used in your ladder program.
SL C 5 00
P rocessor
Thermocouple
Input
Module
Thermocouple or mV
Analog Signals
Channel Data Word
Channel Status Word
C hannel Co nfiguration Word

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Module Overview 1-5
Module Operation
The module’s input circuitry consists of eight differential analog
inputs, multiplexed into an A/D convertor. The A/D convertor reads
the analog input signals and converts them to a digital value. The
input circuitry also continuously samples the CJC sensors and
compensates for temperature changes at the cold junction (terminal
block).
Module Addressing
The module requires eight words each in the SLC processor’s input
and output image tables. Addresses for the module in slot e are as
follows:
I:e.0-7 thermocouple/mV or status data for channels 0 to 7,
respectively (dependent on bit in configuration word).
O:e.0-7 configuration data for channels 0 to 7, respectively.
See Module Addressing on page 3-2 to see the module’s image table.

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1-6 Module Overview
Block Diagram
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Terminal Block Module Circuitry
CJCA Sensor
Shield
Shield
Shield
Shield
CJCB Sensor
User Selected
Filter F requency
Digital
Va lue
Analog to
Digital
Converter
Digital
Filter
multiplexer
Analog
Ground
Wit hin
12.5V
ungrounded
thermocouple
grounded
thermocouple
IMPORTANT When using multiple thermocouples, the potential
between any two channels cannot exceed the
channel-to-channel differential voltage (12.5 volts).
For more information, see Appendix B.

Publication 1746-UM022B-EN-P - January 2005
Module Overview 1-7
Linear Millivolt Device Compatibility
(1)
A large number of millivolt devices may be used with the 1746-NT8
module. For this reason we do not specify compatibility with any
particular device.
However, millivolt applications often use strain gage bridges. A
resistive voltage divider using fixed resistors is recommended for this
application. The circuit diagram below shows how this connection is
made.
(1) Output impedance of input device must be less than 100 ohm to meet accuracy specifications.
TIP The resistors should be selected to ensure that the
differential input voltage is less than or equal to ±100
mV.
+
-
+
Voc
Strain
Gage
Bridge
Channel
Input
fixed
fixed fixed
variable
1746-NT8

Publication 1746-UM022B-EN-P - January 2005
1-8 Module Overview

1Publication 1746-UM022B-EN-P - January 2005
Chapter 2
Installing And Wiring Your Module
Read this chapter to install and wire your module. This chapter
covers:
•avoiding electrostatic damage
•determining power requirements
•installing the module
•wiring signal cables to the module’s terminal block
Electrostatic Damage
Electrostatic discharge can damage semiconductor devices inside this
module if you touch backplane connector pins. Guard against
electrostatic damage by observing the following precautions:
ATTENTION Electrostatically Sensitive Components
•Before handling the module, touch a grounded
object to rid yourself of electrostatic charge.
•Handle the module from the front, away from the
backplane connector. Do not touch backplane
connector pins.
•Keep the module in its static-shield container
when not in use or during shipment.
Failure to observe these precautions can degrade the
module’s performance or cause permanent damage.

Publication 1746-UM022B-EN-P - January 2005
2-2 Installing And Wiring Your Module
Power Requirements
The module receives its power through the SLC 500 chassis backplane
from the fixed or modular +5 V dc/+24 V dc chassis power supply.
The maximum current drawn by the module is shown in the table
below.
Maximum Current Drawn by the Module
Considerations for a Modular System
Place your module in any slot of an SLC 500 modular, or modular
expansion chassis, except for the left-most slot (slot 0) reserved for
the SLC processor or adapter modules.
When using the module with a modular system, add the values shown
above to the requirements of all other modules in the SLC to prevent
overloading the chassis power supply. Refer to the SLC 500 Modular
Hardware Style User Manual, publication 1747-UM011.
5Vdc Amps 24Vdc Amps
0.120 0.070