Rockwell Automation 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

IMPORTANT

ATTENTION

SHOCK HAZARD

BURN HAZARD

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.

Identifies information that is critical for successful application and understanding of the product.

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

Labels may be located on or inside the equipment (e.g., drive or motor) to alert people that dangerous voltage may be present.

Labels may be located on or inside the equipment (e.g., drive or motor) to alert people that surfaces may be dangerous temperatures.

Preface

Module Overview

Installing And Wiring Your Module

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

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

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

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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

Table of Contents ii

Channel Configuration, Data, and Status

Chapter 4

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

Programming Examples

Troubleshooting Your Module

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Chapter 5

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

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

Maintaining Your Module And Safety Considerations

Module Specifications

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

Preventive Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Appendix A

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

Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples

Configuring the 1746-NT8 Module with RSLogix 500

Appendix B

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

Glossary

Index

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Table of Contents iv

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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

updated thermocouple graphs page A-8

configuring NT8 with RSLogix 500 page C-1

page 5-15

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Summary of Changes 2

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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

What This Manual Covers

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.

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.

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Preface 2

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]).

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Chapter

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

Type °C Temperature Range °F Temperature Range

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

Millivolt Input Ranges

-50 to +50 mV

-100 to +100 mV

(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.

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.

(2)

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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.

(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.

Module Overview 1-3

Channel Status LEDs (green)

Module Status LEDs (green)

Removable Terminal Block

CJC Sensors

Cable Tie Slots

INPUT

CHANNEL

014

5 2 123

Door Label

1746-NT8

CJC A+ CJC ACHL 0+ CHL 0SHIELD CHL 1+ CHL 1CHL 2+ CHL 2SHIELD CHL 3+ CHL 3CHL 4+ CHL 4SHIELD CHL 5+ CHL 5CHL 6+ CHL 6SHIELD CHL 7+ CHL 7CJC B+ CJC B-

Jumper - Do not move

JP1

Self-Locking Tabs

STATUS

MODULE

THERMOCOUPLE/mV

Side Label

CAT

SERIAL NO.

1746 NT4

NT4±xxx x

THERMOCOUPLE/mV INPUT MODULE

SLC 500

SER

FRN

)

CLASS I, GROUPS A, B, C AND D, DIV.2

FOR HAZ. LOC. A196

LISTED IND. CONT . EQ.

)

OPERA TING

TEMPERA TURE

CODE T3C

THERMOCOUPLE TYPES:

VOLTAGE:

INPUT SIGNAL RANGES

±100mVDC to +100mVDC

±50mVDC to +50mVDC

J, K, T, E, R, S, B, N

MADE IN USAFAC 1M

Hardware Features

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

System Overview

Door Label Permits easy terminal identification

Cable Tie Slots Secure and route wiring from module

Self Locking Tabs Secure module in chassis slot

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.

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.

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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.

Channel Data Word

Channel Status Word

Therm ocouple or mV Analog Signals

Thermocou ple

Input

Module

Channel Co nfiguration Word

SL C 5 00

P rocess or

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.

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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

ungrounded thermocouple

Wit hin

12.5V

grounded thermocouple

Terminal Block Module Circuitry

CJCA Sens or

Shield

multiplexer

Analog Ground

Analog to

Digital

Converter

User S elected Filter F requency

Shield

CJCB S ensor

Digital

Filter

Digital Va lue

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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.

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.

Strain Gage

Voc

variable

fixed

1746-NT8

Channel

Input

Bridge

fixed

TIP

The resistors should be selected to ensure that the differential input voltage is less than or equal to ±100 mV.

(1) Output impedance of input device must be less than 100 ohm to meet accuracy specifications.

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1-8 Module Overview

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Chapter

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.

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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

5Vdc Amps 24Vdc Amps

0.120 0.070

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.

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Fixed I/O Chassis - I/O Module Compatibility

The following chart depicts the range of current combinations supported by the fixed I/O expansion chassis. To use it, find the backplane current draw and operating voltage for both modules being used in the chassis. These specifications are found in the table alongside the chart.

Next, plot each of the currents on the chart below. If the point of intersection falls within the operating region, the combination is valid. If not, the combination cannot be used in a 2-slot, fixed I/O chassis.

OW16 and

450

400

350

300

250

Current

(mA)

at 5V dc

200

150

100

Example: Plot IN16 and NIO4V IN16 = 0.085 at 5V dc and 0A at 24V dc NIO4V = 0.055A at 5V dc and 0.115A at 24V dc

1. Add current draws of both modules at 5V dc to get

0.14 A (140 mA).

2. Plot this point on the chart above (140 mA at 5V dc.

3. Add current draws of both modules at 24V dc to get

0.115 A (115 mA).

4. Plot current draw at 24V dc (115 mA at 24V dc).

5. Note the point of intersection on the chart above (marked x). This combination falls within the valid operating region for the fixed I/O chassis.

(0, 455)

Valid Operating

Region

50 150 200

100

Current (mA) at 24V

OW16 and IA16

(180, 255)

Plotted from

Example

Shown Below

Installing And Wiring Your Module 2-3

Module Current Draw - Power Supply Loading

I/O Module

BAS .150 .040

BASn .150 .125

DCM .360 .000

FI O4I .055 .150

FI O4V .055 .120

HS .300 .000

HSTP 1 .200 .000

IA4 .035 .000

IA8 .050 .000 NR4 .050 .05 0

IA16 .085 .000

IB8 .050 .000

IB16 .085 .000

IB32 .106 .000

IC16 .085 .000

IG16 .140 .000

IH16 .085 .000

IM4 .035 .000

IM8 .050 .000

IM16 .085 .000

IN16 .085 .000

IO4 .030 .025

IO8 .060 .045

IO12 .090 .070

ITB16 .085 .000

ITV16 .085 .000

IV8 .050 .000

IV16 .085 .000

IV32 .106 .000

KE .150 .040

KEn .125

5V 24V I/O Module 5V 24V

NI4 .025 .085

NI8 .200 .100

NIO4I .055 .145

NIO4V .055 .115

NO4I .055 .195

NO4V .055 .145

120

100 55

120 70

.150

N08I N08V 120 160*

NR8

NT4 .060 .040

NT8

OA16 .370 .00 0

OA8 .185 .000

OAP 12 .370 .000

OB8 .135 .000

OB16 .280 .000

OB16E .135 .000

OB32 .452 .000

OBP8 .135 .000

OBP16 .250 .000

OG16 .180 .00 0

OV8 .135 .000

OV16 .270 .000

OV32 .452 .000

OVP 16 .250 .000

OW16 .170 .180

OW4 .045 .045

OW8 .085 .090

OX8 .085 .090

250*

* w/jumper set to rack, otherwise 0.0 mA.

Important: The 1747-NO4I and 1746-NO4V analog output modules may require an external power supply.

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2-4 Installing And Wiring Your Module

When using the BAS or KE module to supply power to a 1747-AIC Link Coupler, the link coupler draws its power through the module. The higher current drawn by the AIC at 24V dc is shown in the table as BASn (BAS networked) and KEn (KE networked). Be sure to use these current draw values if the application uses the BAS or KE module in this way.

General Considerations

Most applications require installation in an industrial enclosure to reduce the effects of electrical interference. Thermocouple inputs are highly susceptible to electrical noises due to the small amplitudes of their signal (microvolt/°C).

Group your modules to minimize adverse effects from radiated electrical noise and heat. Consider the following conditions when selecting a slot for the thermocouple module. Position the module:

• in a slot away from sources of electrical noise such as recontact

switches, relays, and AC motor drives

• away from modules which generate significant radiated heat,

such as the 32-point I/O modules

In addition, route shielded twisted pair thermocouple or millivolt input wiring away from any high voltage I/O wiring.

Remember that in a modular system, the processor or communications adapter always occupies the first slot of the chassis.

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Module Installation and Removal

ATTENTION

Installing And Wiring Your Module 2-5

Possible Equipment Operation

Before installing or removing your module, always disconnect power from the SLC 500 system and from any other source to the module (in other words, do not ’hot swap’ your module), and disconnect any devices wired to the module.

Failure to observe this precaution can cause unintended equipment operation and damage.

Top and Bottom Module Release(s)

Card Guide

To insert your module into the chassis, follow these steps:

1. Before installing the module, connect the ground wire to TB1.

See the figure on page 2-10.

2. Align the circuit board of your module with the card guides at

the top and bottom of the chassis.

3. Slide your module into the chassis until both top and bottom

retaining clips are secure. Apply firm even pressure on your module to attach it to its backplane connector. Never force your module into the slot.

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2-6 Installing And Wiring Your Module

4. Cover all unused slots with the Card Slot Filler, Allen-Bradley

part number 1746-N2.

Terminal Block Removal

To remove the terminal block:

1. Loosen the two terminal block release screws. To avoid cracking

the terminal block, alternate between screws as you remove them.

2. Using a screwdriver or needle-nose pliers, carefully pry the

terminal block loose. When removing or installing the terminal block be careful not to damage the CJC sensors.

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Terminal block diagram with CJC sensors

CJC Sensors

Recomm ended Torque: wiring screws: 0.25 Nm (2.2 in-lb) release scre ws: 0.25 Nm (2.2 in-lb)

Installing And Wiring Your Module 2-7

Terminal Block Release Screws

ATTENTION

CJC Sensors

Terminal Block Release Screws

Possible Equipment Operation

Before wiring your module, always disconnect power from the SLC 500 system and from any other source to the module.

Failure to observe this precaution can cause unintended equipment operation and damage.

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2-8 Installing And Wiring Your Module

Wiring Your Module

Follow these guidelines to wire your input signal cables:

• Power, input, and output (I/O) wiring must be in accordance

with Class 1, Division 2 wiring methods [Article 501-4(b) of the National Electrical Code, NFPA 70] and in accordance with the authority having jurisdiction.

• Route thermocouple and millivolt signal wires as far as possible

from sources of electrical noise, such as motors, transformers, contactors, and ac devices. As a general rule, allow at least 6 in. (about 15.2 cm) of separation for every 120V ac of power.

• Routing the field wiring in a grounded conduit can reduce

electrical noise further.

• If the field wiring must cross ac or power cables, ensure that

they cross at right angles.

• For high immunity to electrical noise, use Belden™ 8761

(shielded, twisted pair) or equivalent wire for millivolt sensors; or use shielded, twisted pair thermocouple extension lead wire specified by the thermocouple manufacturer. Using the incorrect type of convention thermocouple extension wire or not following the correct polarity may cause invalid readings.

• Ground the shield drain wire at only one end of the cable. The

preferred location is at the shield connections on the terminal block. (Refer to IEEE Std. 518, Section 6.4.2.7 or contact your sensor manufacturer for additional details.)

• Keep all unshielded wires as short as possible.

• Excessive tightening can strip a screw. Tighten screws to 0.25

Nm (2.2 in-lb) or less, based on UL 1059, CSA C22.2 No. 158, VDE 0110B 2.79 standards.

• Follow system grounding and wiring guidelines found in your

SLC 500 Modular Hardware Style User Manual, publication 1747-UM011 or 1747-SLC 500 Fixed Hardware Style User Manual, publication 1747-6.21.

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Installing And Wiring Your Module 2-9

Preparing and Wiring the Cables

To prepare and connect cable leads and drain wires, follow these steps:

Cable

Signal Wires

(Remove foil shield and drain wire from sensor end of the cable.)

Drain Wire

Signal Wires

1. At each end of the cable, strip some casing to expose individual

wires.

2. Trim signal wires to 5-inch lengths beyond the cable casing.

Strip about 3/16 inch (4.76 mm) of insulation to expose the ends of the wires.

3. At the module end of the cables:

• extract the drain wire and signal wires

• remove the foil shield

• bundle the input cables with a cable strap

4. Connect pairs of drain wires together:

• Channels 0 and 1

• Channels 2 and 3

• Channels 4 and 5

• Channels 6 and 7

Keep drain wires as short as possible.

5. Connect the drain wires to the shield inputs of the terminal

block if appropriate for thermocouple used.

• Channel 0 and 1 drain wires to pin 5

• Channel 2 and 3 drain wires to pin 10

• Channel 4 and 5 drain wires to pin 15

• Channel 6 and 7 drain wires to pin 20

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2-10 Installing And Wiring Your Module

6. Connect the signal wires of each channel to the terminal block.

IMPORTANT

Only after verifying that your connections are correct for each channel, trim the lengths to keep them short. Avoid cutting leads too short.

7. Connect TB1 chassis ground connector to the nearest chassis

mounting bolt with 14 gauge wire. (Looking at the face of the module, TB1 is near the lower part of the terminal block on the primary side of the PCB.)

TB1

Connect ground wire to TB1 before installing module.

8. At the sensor end of cables from thermocouple/mV devices:

• remove the drain wire and foil shield

• apply shrink wrap as an option

• connect to mV devices keeping the leads short.

IMPORTANT

If noise persists, try grounding the opposite end of the cable. Ground one end only.

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Terminal Block Diagram with Input Cable

Thermocouple or mV Ca ble

Recommended Torque : TB 1 0.3 to 0.5 Nm (2.5 to 4.5 in-lb)

Installing And Wiring Your Module 2-11

CJC A+

CJC AChannel 0+

Channel 0-

Shield for CH0 and CH 1

Channel 1+

Channel 1-

Channel 2+ Channel 2-

Shield for CH2 and CH 3

Channel 3+

Channel 3Channel 4+

Channel 4Shield for CH4 and CH 5

Channel 5+ Channel 5-

Channel 6+

Channel 6-

Shield for CH6 and CH 7

Channel 7+

Channel 7-

CJC B +

CJC B -

TB1

The module also has a ground terminal TB1, which should be grounded to a chassis mounting bolt with 14-gauge wire.

Cold-Junction Compensation (CJC)

ATTENTION

To obtain accurate readings from each of the channels, the cold-junction temperature (temperature at the module’s terminal junction between the thermocouple wire and the input channel) must be compensated for. Two cold-junction compensating sensors have been integrated in the removable terminal block. They must remain installed.

Possible Equipment Operation

Do not remove or loosen the cold-junction compensating temperature transducers located on the terminal block. Both CJCs are required to ensure accurate thermocouple input readings at each channel. The module will not operate in thermocouple mode if a CJC is not connected.

Failure to observe this precaution can cause unintended equipment operation and damage.

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2-12 Installing And Wiring Your Module

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Chapter

Module ID Code

Considerations Before Using

This chapter explains how the module and the SLC processor communicate through the processor’s I/O image tables. It also describes the module’s input filter characteristics. Topics discussed include:

• module ID code

• module addressing

• channel filter frequency selection

• channel turn-on, turn-off, and reconfiguration times

• response to slot disabling

The module ID code is unique number assigned to each 1746 I/O module. The ID code defines the type of I/O module and the number of words used in the processor’s I/O image table.

Your Module

The module ID code for the 1746-NT8 module is 3533.

No special I/O configuration is required. The module ID automatically assigns the correct number of input and output words.

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3-2 Considerations Before Using Your Module

Module Addressing

SLC 5/0X

Data Files

Slot e

Output Image

Slot e

Input Image

Output

Scan

Input Scan

The following memory map shows you how the SLC processor’s output and input tables are defined for the module.

Image Table

Thermocouple

Module

Image Table

Output Image

8 Words

Input Image

8 Words

Bit 15

Channel 0 Configuration Word

Channel 1 Configuration Word Channel 2 Configuration Word

Bit 15

Channel 3 Configuration Word

Channel 4 Configuration Word Channel 5 Configuration Word

Channel 6 Configuration Word Channel 7 Configuration Word

Channel 0 Data or Status Word Channel 1 Data or Status Word Channel 2 Data or Status Word Channel 3 Data or Status Word

Channel 4 Data or Status Word

Channel 5 Data or Status Word Channel 6 Data or Status Word

Channel 7 Data or Status Word

Bit 0

Word 0

Word 1

Word 2

Word 3

Word 4

Word 5

Word 6

Word 7

Word 0

Word 1

Word 2

Word 3

Word 4

Word 5

Word 6

Word 7

Bit 0

Address

O:e.0

O:e.1

O:e.2

O:e.3

O:e.4

O:e.5

O:e.6

O:e.7

I:e.0

I:e.1

I:e.2

I:e.3

I:e.4

I:e.5

I:e.6

I:e.7

Address

Output Image - Configuration Words

Eight words of the SLC processor’s output image table are reserved for the module. Output image words 0 through 7 are used to configure the module’s input channels 0 through 7. Each output image word configures a single channel and can be referred to as a configuration word. Each word has a unique address based on the slot number assigned to the module.

Example Address - If you want to configure channel 2 on the module located in slot 4 in the SLC chassis, your address would be O:4.2.

Slot

File Type

Elem ent Delimiter

O:4.2

Word

Word Delimiter

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Considerations Before Using Your Module 3-3

Chapter 4 provides detailed bit information about the data content of the configuration word.

Input Image - Data Words and Status Words

Eight words of the SLC processor’s input image table are reserved for the module. Input image words are multiplexed since each channel has one data word and one status word. The corresponding configuration word selects whether the channel status or channel data is in the input image word.

Status bits for a particular channel reflect the configuration settings that you entered into the configuration (output image) word for that channel. To receive valid status, the channel must be enabled and the module must have stored a valid configuration word for that channel.

Each input image word has a unique address based on the slot number assigned to the module.

Channel Filter Frequency Selection

Example Address - To obtain the status/data word of channel 2 (input word 2) of the module located in slot 4 in the SLC chassis use address I:4:2.

File Type

Slot

Word

I:4.2

E lement Delimiter

Word Delimiter

Chapter 4 provides detailed bit information about the content of the data word and the status word.

The thermocouple module uses a digital filter that provides high-frequency noise rejection for the input signals. The digital filter is programmable, allowing you to select from four filter frequencies for each channel. The digital filter provides the highest noise rejection at the selected filter frequency. The graphs to follow show the input channel frequency response for each filter frequency selection.

Selecting a low value (i.e. 10 Hz) for the channel filter frequency provides the best noise rejection for a channel, but it also increases the channel update time. Selecting a high value for the channel filter frequency provides lower noise rejection, but decreases the channel update time.

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3-4 Considerations Before Using Your Module

The following table shows the available filter frequencies, cut-off frequency, step response, and a DC effective resolution for each filter frequency.

Cut-off frequency, Step Response Time, and Effective Resolution (Based on Filter Frequency)

Filter Frequency Cut-Off Frequency Step Response ADC Effective

Resolution

10 Hz 2.62 Hz 400 ms 20.5

50 Hz 13.1 Hz 80 ms 19.0

60 Hz 15.72 Hz 66.7 ms 19.0

250 Hz 65.5 Hz 16 ms 15.5

The step response is calculated by a 4 x (1/filter frequency) settling time.

Channel Cut-Off Frequency

The channel filter frequency selection determines a channel’s cut-off frequency, also called the -3 dB frequency. The cut-off frequency is defined as the point on the input channel frequency response curve where frequency components of the input signal are passed with 3 dB of attenuation. All frequency components at or below the cut-off frequency are passed by the digital filter with less than 3 dB of attenuation. All frequency components above the cut-off frequency are increasingly attenuated, as shown in the graphs on page 3-5.

The cut-off frequency for each input channel is defined by its filter frequency selection. The table above shows the input channel cut-off frequency for each filter frequency. Choose a filter frequency so that your fastest changing signal is below that of the filter’s cut-off frequency. The cut-off frequency should not be confused with update time. The cut-off frequency relates how the digital filter attenuates frequency components of the input signal. The update time defines the rate at which an input channel is scanned and its channel data word updated.

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Signal Attenuation with 10 Hz Input Filter

Considerations Before Using Your Module 3-5

-3 dB

-20

-40

-60

-80

Amplitude (in dB)

-100

-120

-140

-160

-180

-200

2.62 Hz

Signal Attenuation with 50 Hz Input Filter

-3 dB

Amplitude (in dB)

-20

-40

-60

-80

-100

-120

-140

-160

-180

-200 0 50 100 150 200 250 300 Hz

Signal Frequency

60 Hz

13.1 Hz

Signal Frequency

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3-6 Considerations Before Using Your Module

Signal Attenuation with 60 Hz Input Filter

-3 dB

Amplitude (in dB)

-20

-40

-60

-80

-100

-120

-140

-160

-180

-200 0 60 120 180 240 300 360 Hz

15.7 Hz

Signal Attenuation with 250 Hz Input Filter

-3 dB

Amplitude (in dB)

-20

-40

-60

-80

-100

-120

-140

-160

-180

-200 0 250 500 750 1000 1250 1500 Hz

Signal Fr equency

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65.5 Hz

Signal Fr equency

Channel Step Response

The channel filter frequency determines the channel’s step response. The step response is time required for the analog input signal to reach 95% of its expected, final value given a full-scale step change in the input signal. This means that if an input signal changes faster than the channel step response, a portion of that signal will be attenuated by the channel filter. The table on page 3-4 shows the step response for each filter frequency.

Considerations Before Using Your Module 3-7

Update Time

The thermocouple module update time is defined as the time required for the module to sample and convert the input signals of all enabled input channels and make the resulting data values available to the SLC processor. It can be calculated by adding the sum of all enabled sample times, plus a CJC update time.

Channel 0 Disabled Channel 1 Disabled

Enabled

Sample

Channel 0

Update CJC

Enabled Enabled Enabled

Sample

Channel 1

Calculate Previous

The following table shows the channel sampling time for each filter frequency. It also gives the CJC update time.

Channel Sampling Time

Channel Sampling Time for Each Filter Frequency (all values ±1 ms)

CJC Update Time 250 Hz Filter 60 Hz Filter 50 Hz Filter 10 Hz Filter

290 ms 66 ms 125 ms 140 ms 470 ms

Channel 2 Disabled Channel 7 Disabled

Sample

Channel 2

Calculate Previous

Sample

Channel 7

Calculate Previous

Sample

CJC

Channel

Calculate Previous

The times above include a settling time necessary between input channel readings. The sampling times for filter frequencies listed do not include a 45 ms open-circuit detection time utilized when the channel is configured for open-circuit detection. CJC open-circuit detection does not require the additional 45 ms settling time.

The fastest module update time occurs when only one channel with a 250 Hz filter frequency is enabled.

Module update time = 290 ms + 66 ms = 356 ms

The slowest module update time occurs when eight channels, each using a 10 Hz filter frequency, are enabled.

Module update time = 290 ms + 470 ms + 470 ms + 470 ms + 470 ms + 470 ms + 470 ms + 470 ms + 470 ms = 4.05 s

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3-8 Considerations Before Using Your Module

Update Time Calculation Example

The following example shows how to calculate the module update time for the given configuration:

Channel 0 configured for 250 Hz filter frequency, enabled Channel 1 configured for 250 Hz filter frequency, enabled Channel 2 configured for 50 Hz filter frequency, enabled Channel 3 through 7 disabled

Using the values from the table on page 3-7, add the sum of all enabled channel sample times, plus one CJC update time.

Channel 0 sampling time = 66 ms

Channel 1 sampling time = 66 ms

Channel 2 sampling time = 140 ms

CJC update time = 290 ms

Module update time = 562 ms

Channel Turn-On, Turn-Off, and Reconfiguration Times

Auto-calibration

The time required for the module to recognize a new configuration for a channel is generally one module update time plus 890 µs per newly configured channel. If the filter frequency selected for the newly enabled, configured channel is new to the module, then auto-calibration is performed following configuration recognition.

Turn-off time requires up to one module update time.

Reconfiguration time is the same as turn-on time.

Auto-calibration is performed by the module to correct for drift errors over temperature. Auto-calibration occurs immediately following configuration of a previously unselected filter frequency, and generally every two minutes for all selected filter frequencies of the system. The time required to perform auto-calibration is defined as follows:

Auto-calibration Time

250 Hz Filter 60 Hz Filter 50 Hz Filter 10 Hz Filter

325 ms 525 ms 585 ms 1.975 s

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Considerations Before Using Your Module 3-9

CJC sensors are acquired at 60 Hz to maximize the trade-off between resolution and update rate. For example, if some channels are acquired at 250 Hz and some are acquired at 50 Hz, then the total auto-calibration time would be:

Frequency Auto-Calibration

250 Hz 325 ms

60 Hz 525 ms

50 Hz 585 ms

1.435 s Total

During auto-calibration, input values are not updated.

Response to Slot Disabling

By writing to the status file in the modular SLC processor, you can disable any chassis slot. Refer to your SLC programming manual for the slot disable/enable procedure.

ATTENTION

Possible Equipment Operation

Always understand the implications of disabling a module before using the slot disable feature.

Failure to observe this precaution can cause unintended equipment operation.

Input Response

When a thermocouple slot is disabled, the thermocouple module continues to update its input image table. However, the SLC processor does not read input from a module that is disabled. Therefore, when the processor disables the thermocouple module slot, the module inputs appearing in the processor image table remain in their last state, and the module’s updated image table is not read. When the processor re-enables the module slot, the current state of the module inputs are read by the processor during the subsequent scan.

Output Response

The SLC processor may change the thermocouple module output data (configuration) as it appears in the processor output image. However, this data is not transferred to the thermocouple module. The outputs are held in their last state. When the slot is re-enabled, the data in the processor image is transferred to the thermocouple module.

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3-10 Considerations Before Using Your Module

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Chapter

Channel Configuration, Data, and Status

Read this chapter to:

• configure each input channel

• check each input channel’s configuration and status

Channel Configuration

Channel configuration words appear in the SLC processor’s output image table as shown below. Words 0 to 7 correspond to module channels 0 to 7.

After module installation, configure each channel to establish the way the channel operates (e.g., thermocouple type, temperature units, etc.). Configure the channel by setting bits in the configuration word using your programming device. The SLC configuration words are shown below.

SLC Output Image (Configuration) Words

bit 0

O:e.0

O:e.1

O:e.2

O:e.3

O:e.4

bit 15

Channel 0 Channel Configuration Word

Channel 1 Channel Configuration Word

Channel 2 Channel Configuration Word

Channel 3 Channel Configuration Word

Channel 4 Channel Configuration Word

O:e.5

O:e.6

O:e.7

Channel 5 Channel Configuration Word

Channel 6 Channel Configuration Word

Channel 7 Channel Configuration Word

e = slot number of the module

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4-2 Channel Configuration, Data, and Status

The configuration word default settings are all zero. Next, we describe how you set configuration bits of a channel configuration word to set up the following channel parameters:

• data format such as engineering units, counts, or scaled-for-PID

• how the channel should respond to a detected open-input

circuit

• filter frequency selection

• temperature units in °C or °F

• whether the channel is enabled or disabled

• whether status or data information is selected for the module’s

input image table

Channel Configuration Procedure

The channel configuration word consists of bit fields, the settings of which determine how the channel operates. This procedure looks at each bit field separately and helps configure a channel for operation. Refer to the chart on page 4-4 and the bit field descriptions that follow for complete configuration information.

TIP

1. Determine which channels are used in your program and enable

them. Place a one in bit 0 if the channel is to be enabled. Place a zero in bit 0 if the channel is to be disabled.

2. Determine the input device type (J, K, etc. thermocouple) (or

mV) for a channel and enter its respective four-digit binary code in bit field 1 through 4 of the channel configuration word.

3. Select a data format for the data word. Your selection determines

how the analog input value from the A/D converter will be expressed in the data word. Enter your two-digit binary code in bit field 5 and 6 of the channel configuration word.

When using RSLogix 500 version 6.10 or higher, you can use the software’s I/O wizard to configure the NT8 channels. Refer to Appendix C for more information.

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4. Determine the desired state for the channel data word if an

open-circuit condition is enabled and detected for that channel. Enter the two-digit binary code in bit field 7 and 8 of the channel configuration word.

Channel Configuration, Data, and Status 4-3

5. If the channel is configured for thermocouple inputs, determine

if the channel data word should read in degrees Fahrenheit or degrees Celsius and enter a one or a zero in bit 9 of the configuration word. If the channel is configured for a mV analog sensor, enter a zero in bit 9.

6. Determine the desired input filter frequency for the channel and

enter the two-digit binary code in bits 10 and 11 of the channel configuration word. A lower filter frequency increases the channel update time, but also increases the noise rejection and channel resolution. A higher filter frequency decreases the channel update time, but also decreases the noise rejection and effective resolution.

7. Ensure that bits 12 through 14 contain zeros.

8. Determine whether the channel input image word should

contain data or status. Place a one in bit 15 if channel data is desired. Place a zero in bit 15 if status is desired.

9. Build the channel configuration word for every channel on each

thermocouple/mV module repeating the procedures given in steps 1 through 8.

10. Enter this configuration into your ladder program and download

it to the thermocouple module.

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4-4 Channel Configuration, Data, and Status

A detailed explanation appears in the following table:

Channel Configuration Word (0:e.0 through 0:e.7) - Bit Definitions

To Select Make these bit settings

1514131211109876543210

Channel Enable

Input Ty pe

Data Format

Open Circuit

Temperature units

Channel filter frequency

Unused

Input Image Ty pe

(1) For engineering units x 1, values are expressed in 0.1 degrees or 0.01 mV. For engineering units x 10, values are expressed in 1.0 degrees or 0.1 mV.

(2) When millivolt input type is selected, the bit setting for temperature units is ignored.

(3) Ensure unused bits 12 through 14 are always set to zero.

Channel Disable Channel Enable Thermocouple J Thermocouple K 00 Thermocouple T 00 Thermocouple E 00 Thermocouple R 01 Thermocouple S 01 Thermocouple B 01 Thermocouple N 01

-50 to +50 mV 10

-100 to +100 mV 10 Invalid 10 Invalid 10 Invalid 11 Invalid 11 Invalid 11 CJC temperature 11

Engineering Units x 1

Engineering Units x 10 Scaled-for-PID Proportional counts

Zero on open circuit Max. on open circuit Min. on open circuit Disabled

(2)

°C

(2)

°F 10 Hz input filter 50 Hz input filter

60 HZ input filter 250 Hz input filter

(3)

Unused Invalid

Status Word Data Word

(1)

00 01 10 11

0 1

00 01 10 11

000

111 0 1

00 01 10

1 00 01 10 11 00 01 10 11 00 01 10 11 00 01 10 11

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Channel Configuration, Data, and Status 4-5

Select Channel Enable (Bit 0)

Use the channel enable bit to enable a channel. The thermocouple module only scans enabled channels. To optimize module operation and minimize throughput times, unused channels should be disabled by setting the channel enable bit to zero (default value).

When set (1) the channel enable bit is used by the module to read the configuration word information selected. While the enable bit is set, modification of the configuration word may lengthen the module update time for one cycle. If any change is made to the configuration word, the change is reflected in the status word before new data is valid (described on page 4-11).

While the channel enable bit is cleared (0), the associated channel data/status word values are cleared. After the channel enable bit is set (1), the associated channel data/status word remains cleared until the thermocouple module sets the channel status bit (bit 0) in the channel status word.

Select Input Types (Bits 1 through 4)

The input type bit field lets you configure the channel for the type of input device you have connected to the module. Valid input devices are types J, K, T, E, R, S, B, and N thermocouple sensors and ±50 mV and ±100 mV analog input signals. The channel can also be configured to read the cold-junction temperature calculated for that specific channel. When the cold-junction compensation (CJC) temperature is selected, the channel ignores the physical input signal.

Select Data Format (Bits 5 and 6)

The data format bit field lets you define the expressed format for the channel data word contained in the module input image. The data types are engineering units, scaled-for-PID, and proportional counts.

The engineering units allow you to select from two resolutions, x1 or x10. For engineering units x1, values are expressed in 0.1 degrees or 0.01 mV. For engineering units x10, values are expressed in 1.0 degrees or 0.1 mV. (Use the x10 setting to produce temperature readings in whole degrees Celsius or Fahrenheit.)

The scaled-for-PID value is the same for millivolt, thermocouple, and CJC input types. The input signal range is proportional to your selected input type and scaled into a 0 through 16,383 range, which is standard to the SLC PID algorithm.

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4-6 Channel Configuration, Data, and Status

The proportional counts are scaled to fit the defined temperature or voltage range. The input signal range is proportional to your selected input and scaled into a -32,768 to 32,767 range.

Using Scaled-for-PID and Proportional Counts

The thermocouple module provides eight options for displaying input channel data. These are 0.1°F, 0.1°C, 1°F, 1°C, 0.01 mV, 0.1 mV, Scaled-for-PID, and Proportional Counts. The first six options represent real Engineering Units displayed by the 1746-NT8 and do not require explanation. The Scaled-for-PID and Proportional Counts selections provide the highest NT8 display resolution, but also require you to manually convert the channel data to real Engineering Units.

The equations below show how to convert from Scaled-for-PID to Engineering Units, Engineering Units to Scaled-for-PID, Proportional Counts to Engineering Units, and Engineering Units to Proportional Counts. To perform the conversions, use the defined temperature or millivolt range for the channel’s input type. See the Channel Data Word Format table on page 4-8. The lowest possible value for an input type is S

, and the highest possible value is S

LOW

HIGH

Effective Resolutions

The effective resolution for an input channel depends upon the filter frequency selected for that channel.

Publication 1746-UM022B-EN-P - January 2005

Scaling Examples

Equation: Engineering Units Equivalent = S

Data: Assume type J input type, scaled-for-PID display type, channel data = 3421.

Solution: Engineering Units Equivalent = -210°C + [(760°C-(-210°C)) x (3421/16384)] = -7.46°C.

Equation: Scaled-for-PID Equivalent = 16384 x [(Engineering Units desired -S

Data: Assume type J input type, scaled-for-PID display type, desired channel temp. = 344°C.

Solution: Scaled-for-PID Equivalent = 16384 x [(344°C - (-210°C))/(760°C - (-210°C))] = 9357

Equation: Engineering Units Equivalent = S

Data: Assume type E input type, proportional counts display type, channel data = 21567.

Solution: Engineering Units Equivalent = -454°F + {[1832°F -(-454°F)] x [(21567 + 32768)/65536]} = 1441.3°F

Scaled-for-PID to Engineering Units

+ [(S

LOW

HIGH-SLOW

Want to calculate °C equivalent. From Channel Data Word Format table, S

LOW

Engineering Units to Scaled-for-PID

Want to calculate Scaled-for-PID equivalent. From Channel Data Word Format table, S

LOW

Proportional Counts to Engineering Units

+ {(S

LOW

HIGH-SLOW

32768)/ 65536]}

Want to calculate °F equivalent. From Channel Data Word Format table, S

LOW

Channel Configuration, Data, and Status 4-7

) x (Scaled-for-PID value displayed/16384)]

= -210°C and S

HIGH

= 760°C.

)/(SHIGH-S

LOW

= 760°C.

) x [(Proportional Counts value displayed +

= -454°F and S

HIGH

=1832°F

LOW

)]

Engineering Units to Proportional Counts

Equation:

Proportional Counts Equivalent = {65536 x[(Engineering Units desired - S

LOW

)/(S

HIGH-SLOW

)]} -32768

Data: Assume type E input type, proportional counts display type, desired channel temp. = 1000°F.

Want to calculate Proportional Counts equivalent. From Channel Data Word Format table, SLOW = -454°F and SHIGH = 1832°F. Proportional Counts Equivalent = {65536 x[100°F - (-454°F)/(1832°F - (-454°F)]} - 32768 = 8916.

Solution: Proportional Counts Equivalent = {65536 x[1000°F - (-454°F)/(1832°F - (-454°F)]} - 32768 = 8916.

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4-8 Channel Configuration, Data, and Status

1746-NT8 Thermocouple Module - Channel Data Word Format

Data Format

Input Type Engineering Units x10 Engineering Units x1 Scaled for PID Proportional

°Celsius °Fahrenheit °Celsius °Fahrenheit

Counts

J -210 to +760 -346 to +1400 -2100 to +7600 -3460 to +14000 0 to +16383 -32768 to +32767

K -270 to +1370 -454 to +2498 -2700 to +13700 -4540 to +24980 0 to +16383 -32768 to +32767

T -270 to +400 -454 to +752 -2700 to +4000 -4540 to +7520 0 to +16383 -32768 to +32767

E -270 to +1000 -454 to +1832 -2700 to +10000 -4540 to +18320 0 to +16383 -32768 to +32767

R 0 to +1768 +32 to +3214 0 to +17680 +320 to+32140 0 to +16383 -32768 to +32767

S 0 to +1768 +32 to +2372 0 to +17680 +320 to +32140 0 to +16383 -32768 to +32767

B +300 to +1820 +572 to +3308 +3000 to +18200

+5720 to +3276.7

(2)

0 to +16383 -32768 to +32767

N 0 to +1300 +32 to +2372 0 to +13000 +320 to +23720 0 to +16383 -32768 to +32767

±50 mV

±100 mV

(1)

-500 to +500 -500 to +500 -5000 to +5000 -5000 to +5000 0 to +16383 -32768 to +32767

-1000 to +1000 -1000 to +1000 -10000 to +1000 -10000 to +10000 0 to +16383 -32768 to +32767

CJC Sensor -25 to +105 -13 to +221 -250 to +1050 -130 to +2210 0 to +16383 -32768 to +32767

(1) When millivolts are selected, the temperature setting is ignored. Analog input data is the same for either °C or °F selection.

(2) Type B thermocouple cannot be represented in engineering units x1 (°F) above 3276.7°F. Software treats it as an over range error.

1746-NT8 Thermocouple Module - Channel Data Word Resolution

Data Format

Input Ty pe

Engineering Units x10 Engineering Units x1 Scaled for PID Proportional Counts

°Celsius °Fahrenheit °Celsius °Fahrenheit °Celsius °Fahrenheit °Celsius °Fahrenheit

J 1°C/step 1°F/step 1°C/step 1°F/step 0.0592°C/step 0.1066°F/step 0.0148°C/step 0.0266°F/step

K 1°C/step 1°F/step 1°C/step 1°F/step 0.1001°C/step 0.1802°F/step 0.0250°C/step 0.0450°F/step

T 1°C/step 1°F/step 1°C/step 1°F/step 0.0409°C/step 0.0736°F/step 0.0102°C/step 0.0184°F/step

E 1°C/step 1°F/step 1°C/step 1°F/step 0.0775°C/step 0.1395°F/step 0.0194°C/step 0.0349°F/step

R 1°C/step 1°F/step 1°C/step 1°F/step 0.1079°C/step 0.1942°F/step 0.0270°C/step 0.0486°F/step

S 1°C/step 1°F/step 1°C/step 1°F/step 0.1079°C/step 0.1942°F/step 0.0270°C/step 0.0486°F/step

B 1°C/step 1°F/step 1°C/step 1°F/step 0.0928°C/step 0.1670°F/step 0.0232°C/step 0.0417°F/step

N 1°C/step 1°F/step 1°C/step 1°F/step 0.0793°C/step 0.1428°F/step 0.0198°C/step 0.0357°F/step

(1)

±50 mV

±100 mV

CJC

0.1mV/step 0.1mV/step 0.1mV/step 0.1mV/step 6.104µV/step 6.104µV/step 1.526µV/step 1.526µV/step

(1)

0.1mV/step 0.1mV/step 0.1mV/step 0.1mV/step 12.21µV/step 12.21µV/step 3.052µV/step 3.052µV/step

1°C/step 1°F/step 1°C/step 1°F/step 0.0079°C/step 0.0143°F/step 0.0020°C/step 0.0036°F/step

Sensor

(1) When millivolts are selected, the temperature setting is ignored. Analog input data is the same for either °C or °F selection.

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Channel Configuration, Data, and Status 4-9

IMPORTANT

Data resolution is not equivalent to data accuracy. Input accuracy of ±50 µV may span multiple steps for PID and Proportional Counts data types. As an example, a Type B thermocouple temperature range of 0 to 1820°C provides a voltage input range of 0 to

13.82mV to the 1746-NT8. This is a very small input range and, when it is scaled to PID or proportional counts ranges, a small input change results in many counts being changed.

Select Open-Circuit State (Bits 7 and 8)

The open-circuit bit field lets you define the state of the channel data word when an open-circuit condition is detected for that channel. This feature can be disabled by selecting the disable option.

An open-circuit condition occurs when the thermocouple itself or its extension wire is physically separated or open. This can happen if the wire gets cut or disconnected from terminal block.

If either of the two CJC devices is removed from the terminal block, any input channel configured for either a thermocouple or CJC temperature input is placed in an open-circuit condition. An input channel configured for millivolt input is not affected by CJC open circuit conditions.

The results of the data word in an open-circuit condition depend upon the selection of bits 7 and 8.

If zero is selected (00), the channel data word is forced to 0 during an open-circuit condition.

Selecting maximum forces the (01) channel data word value to its full scale value during an open-circuit condition. The full scale value is determined by the selected input type and data format.

Selecting minimum forces the (10) channel data word value to its low scale value during an open-circuit condition. The low scale value is determined by the selected input type and data format.

Disabling the open-circuit selection (11) may result in unintended operation on a failure. Generally, with the open-circuit option disabled, the data word remains unchanged. The open-circuit error bit and the channel LED flags the condition until the error is resolved.

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4-10 Channel Configuration, Data, and Status

For example, if channel one is configured as a thermocouple type when the CJC breaks in an open-circuit condition, if open-circuit detection is disabled, the data word remains unchanged. If the circuit selection is set at minimum, the data word is set to the low scale value for the range and format.

IMPORTANT

Enabling the open-circuit function adds approximately 45 ms to the channel update time. Disabling the open circuit detection removes the time adder. CJC sensors do not require the additional time; thus it is recommended that when using a channel for CJC sensor acquisition, the open-circuit selection is enabled.

Select Temperature Units (Bit 9)

The temperature units bit lets you select temperature engineering units for thermocouple and CJC input types. Units are either degrees Celsius (°C) or degrees Fahrenheit (°F). This bit field is only active for thermocouple and CJC input types. It is ignored when millivolt inputs types are selected.

IMPORTANT

If you are using engineering units (x1 mode) and Fahrenheit temperature units (i.e. 0.1°F), the full scale temperature for thermocouple type B is not achievable with 16-bit signed numerical representation. An over-range error occurs for that channel if it tries to represent the full scale value. The maximum representable temperature is 3276.7°F (instead of 3308°F).

Publication 1746-UM022B-EN-P - January 2005

Select Channel Filter Frequency (Bits 10 and 11)

The channel filter frequency bit field lets you select one of four filters available for a channel. The filter frequency affects the channel update time and noise rejection characteristics. A smaller filter frequency increases the channel update time, but also increases the noise rejection and channel resolution. A larger filter frequency decreases the noise rejection, but also decreases the channel update time and channel resolution.

Channel Configuration, Data, and Status 4-11

Guidelines for filter frequency are listed below.

• 250 Hz setting provides minimal noise filtering.

• 60 Hz setting provides 60 Hz AC line noise filtering.

• 50 Hz setting provides 50 Hz AC line noise filtering.

• 10 Hz setting provides both 50 Hz and 60 Hz AC line noise

filtering.

When a CJC input type is selected, filter frequency is ignored. To maximize the speed versus resolution trade-off, CJC inputs are sampled at 60 Hz.

Unused Bits (Bits 12 through 14)

Bits 12-14 are not defined. Ensure these bits are always cleared (0).

Channel Data/Status Word

Select Input Image Type (Bit 15)

The input image type bit allows you to select data or status information in the channel’s input image word. When set (1), the module places channel data in the corresponding input image word. When the bit is cleared (0) the module places channel status in the corresponding input image word.

The actual thermocouple or millivolt input data values or channel status reside in I:e.0 through I:e.7 of the thermocouple module input image file. The data values present depend on the input type and data formats you have selected. When an input channel is disabled, its data word is reset (0).

Module Input Image (Data/Status) Word

I:e.0

I:e.1

I:e.2

I:e.3

Channel 0 Channel Data/Status Word

Channel 1 Channel Data/Status Word

Channel 2 Channel Data/Status Word

Channel 3 Channel Data/Status Word

I:e.4

I:e.5

I:e.6

I:e.7

Channel 4 Channel Data/Status Word

Channel 5 Channel Data/Status Word

Channel 6 Channel Data/Status Word

Channel 7 Channel Data/Status Word

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4-12 Channel Configuration, Data, and Status

Channel Status Checking

You can use the information provided in the status word to determine if the input configuration data for any channel is valid per your configuration in O:e.0 through O:e.7.

The channel status can be analyzed bit by bit. In addition to providing information about an enabled or disabled channel, each bit’s status (0 or 1) tells you how the input data from the thermocouple or millivolt analog sensor connected to a specific channel will be translated for your application. The bit status also informs you of any error condition and can tell you what type of error occurred.

A bit-by-bit examination of the status word is provided in the chart on the following page.

Channel 0 to 7 Status Word (I:e.0 through I:e.7) - Bit Definitions

To Select Make these bit settings

1514131211109876543210

Channel Channel Disable Status Channel Enable

Thermocouple J Thermocouple K 00 Thermocouple T 00 Thermocouple E 00 Thermocouple R 01 Thermocouple S 01 Thermocouple B 01

Input Ty pe

Data Format

Open Circuit

Temperature units

Thermocouple N 01

-50 to +50 mV 10

-100 to +100 mV 10 Invalid 10 Invalid 10 Invalid 11 Invalid 11 Invalid 11 CJC temperature 11 Engineering Units x 1 Engineering Units x 10 Scaled-for-PID Proportional counts Zero on open circuit Max. on open circuit Min. on open circuit Disabled °C °F

0 1

00 01 10 11

1 00 01 10 11 00 01 10 11 00 01 10 11 00 01 10 11

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Channel 0 to 7 Status Word (I:e.0 through I:e.7) - Bit Definitions

To Select Make these bit settings

1514131211109876543210

10 Hz input filter

Channel filter frequency

Open-circuit error

Under-range error

Over-range error

Channel error No error

50 Hz input filter 60 HZ input filter 250 Hz input filter No error Open circuit detected No error Under range condition No error Over range condition

Channel error

1 0 1

Channel Configuration, Data, and Status 4-13

00 01 10 11

TIP

It takes one timing cycle to complete an update. (Refer to Chapter 3 for module update times.)

IMPORTANT

If the channel for which you are seeking status is disabled, all bit fields are cleared. The status word for any disabled channel is always 0000 0000 0000 0000 regardless of any previous setting that may have been made to the configuration word.

Explanations of the status conditions follow.

Channel Status (Bit 0)

The channel status bit indicates operational state of the channel. When the channel enable bit is set in the configuration word, the thermocouple module configures the selected channel and takes a data sample for the channel data word before setting this bit in the status word.

Input Type Status (Bits 1 through 4)

The input type bit field indicates what type of input signal you have configured for the channel. This field reflects the input type defined in the channel configuration word.

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4-14 Channel Configuration, Data, and Status

Data Format Type Status (Bits 5 and 6)

The data format bit field indicates the data format you have defined for the channel. This field reflects the data type selected in bits 5 and 6 of the channel configuration word.

Open-Circuit Type Status (Bits 7 and 8)

The open-circuit bit field indicates how you have defined the open-circuit bits configuration word, and therefore, the response of the thermocouple module to an open-circuit condition. This feature is active for all input types, including CJC temperature input.

Temperature Units Type Status (Bit 9)

The temperature units field indicates the state of the temperature units bit in the configuration word (bit 9).

Channel Filter Frequency (Bits 10 and 11)

The channel filter frequency bit field reflects the filter frequency you selected in the configuration word.

Open-Circuit E

This bit is set (1) whenever a configured channel detects an open circuit condition at its input. An open-circuit at the CJC sensor also flags this error if the channel input type is either thermocouple or CJC temperature. A range error on the CJC sensor also flags this bit if the input type is thermocouple.

Under-Range Error (Bit 13)

This bit is set (1) whenever a configured channel detects an under range condition for the channel data. An under-range condition exists when the input value is equal to or below the specified lower limit of the particular sensor connected to that channel.

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Channel Configuration, Data, and Status 4-15

Over-Range Error (Bit 14)

This bit is set (1) whenever a configured channel detects an over range condition for the channel data. An over-range condition exists when the input value is equal to or above the specified upper limit of the particular sensor connected to that channel.

Channel Error (Bit 15)

This bit is set (1) whenever a configured channel detects an error in the configuration word, or an error has occurred while acquiring the A/D data value. If during the auto-calibration process, the module detects an out-of-range condition for the filter frequency selected for the channel, the channel error bit is set. An out-of-range condition occurring during auto-calibration would be the result of an overly noisy environment, whereby the module cannot maintain accuracy specifications, thus flagging an error. The error bit is cleared when the error condition is resolved. The channel data word is not updated during a period of auto-calibration filter frequency tolerance errors.

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4-16 Channel Configuration, Data, and Status

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Chapter

Programming Examples

Earlier chapters explained how the configuration word defines the way a channel operates. This chapter shows the programming required to configure the module. It also provides you with segments of ladder logic specific to unique situations that might apply to your programming requirements. The example segments include:

• basic example

• automatic monitoring thermocouples and CJC sensors

• verifying channel configuration changes

• interfacing to the PID instruction

• monitoring channel status bits

• PLC 5 example with NT8 in Remote I/O rack

To enter data into the channel configuration word (O:e.0 through O:e.7) when the channel is disabled (bit 0 = 0), follow these steps. Refer to the table on page 4-4 for specific configuration details.

Example - Configure eight channels of a thermocouple module residing in slot 3 of 1746 chassis. Configure each channel with the same parameters.

Channel Configuration

15 14 13 12 11 10

1 1

000

00 1 00 01 0001

87 65 4321

Configure Channel for:

Channel E Enable Bit Type K Thermocouple Input Engineering Units X 10 Zero if Open Circuit Fahrenheit 10 Hz Filter Frequency Not Used Data Word

The following procedure transfers configuration data and sets the channel enable bits of all eight channels with a single File Copy instruction.

1 Publication 1746-UM022B-EN-P - January 2005

5-2 Programming Examples

Procedure

1. Create integer file N10. Integer file N10 should contain eight

elements (N10:0 through N10:7).

2. Using the programming software, enter the configuration

parameters for all eight thermocouple channels into data file locations N10:0 through N10:7.

Data table for initial programming

Data File N10 (bin) - NT 8 Configuration

Offset1514131211109876543210SymbolDescription

N10:01000001000100011

N10:11000001000100011

N10:21000001000100011

N10:31000001000100011

N10:41000001000100011

N10:51000001000100011

N10:61000001000100011

N10:71000001000100011

3. Program a rung in your ladder logic to copy the contents of

integer file N10 to the eight consecutive output words of the thermocouple module beginning with O:3.0.

Initial programming example

During the first pass, send the channel configuration data to the thermocouple module.

F irst Pass

S:1

0000

0001

On power up, bit S:1/15 is set for the first program scan. During the first program scan, the configuration data in N10:0 through N10:7 will be sent to the 1746-NT8 channel configuration words.

#NT8_CONFIGURATION

COP

COP Copy File Source #N10:0 Dest #O:3.0 Length 8

END

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Programming Examples 5-3

Automatic Monitoring Thermocouples and CJC Sensors

The following example explains how to change data in the channel configuration word when the channel is currently enabled.

Example - Execute a dynamic configuration change to channel 0 of the thermocouple module located in slot 1 of a 1746 chassis. Periodically (e.g., every 60 seconds) change from monitoring an external type K thermocouple to monitoring the CJC sensors mounted on the terminal block. The CJC reading gives a good indication of what the temperature is inside the control cabinet. Finally, set channel 0 back to type K thermocouple.

IMPORTANT

TIP

During configuration alteration, the state of each modified channel can not be determined until after one module update time.

N10:2/1 through N10:2/4 have the input type for type K Thermocouple (0001). N10:8/1 through N10:8/4 have the input type for CJC Temperature Sensor (1111).

Verifying Configuration Changes

When executing a dynamic channel configuration change, there is always a delay from the time the ladder program makes the change to the time the 1746-NT8 supplies a data word using that new configuration information. Also, the ladder program should use the thermocouple temperature data location N10:20 for thermocouple temperature readings and data location N10:12 for CJC temperature readings.

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5-4 Programming Examples

During the first pass, send the channel configuration data to the thermocouple module.

#NT8_CONFIGURATION

COP

COP Copy File Source #N10:0 Dest #O:1.0 Length 8

CHECKING_CJC

B3:6

0000

F irst Pa ss

S:1

If not Checking CJC, copy Channel 0 temperature data into data location for use. Temperature control logic should use N10:20 rather than the TC image (I:1.0) to eliminate problems during CJC checking.

CHECKING_CJC

0001

B3:6

Copy temperature data from Channels 1 to 7 to data registers for use.

0002

CH0_TEMP

MOV

MOV Move Source I:1.0

Dest N10:20

COP

COP Copy File Source #I:1.1 Dest #N10:21 Length 7

Repeating 60 seconds timer (T 11:0) which starts the CJC check cycle.

CJC_CYCLE_TMR/DN

T11:0

0003

CJC_CYCLE_TMR

TON

TON Timer On Delay Timer T11:0 Time Base 1.0 Preset 60< Accum 20<

Every 60 seconds, start CJC check cycle by changing Channel 0 configuration word and latching Checking CJC bit (B3/100).

0004

CJC_CYCLE_TMR/DN

T11:0

NT8_CONFIGURATION

MOV

MOV Move Source N10:8

-32737<

Dest O:1.0

-32767<

U 4

3744<

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CHECKING_CJC

B3:6

L 4

Programming Examples 5-5

0005

0006

0007

Wait 7 seconds for Channel 0 to accept CJC configuration and provide a data value (time depends on module configuration).

CHECKING_CJC

B3:6

CJC_CFG_TMR

TON

TON Timer On Delay Timer T11:1 Time Base 1.0 Preset 7< Accum 0<

Copy CJC Temperature (I:1.0) into CJC register (N10:12)

CJC_CFG_TMR/DN

T11:1

Move Channel 0’s regular configuration word into the Channel 0 configuration word and start timer to ensure word has been accepted prior to taking the thermocouple temperature readings.

CJC_CFG_TMR/DN

T11:1

B3:0 OSR

REG_CFG_TMR

Timer On Delay Timer T11:2 Time Base 1.0 Preset 7< Accum 0<

CJC_TEMP

MOV

MOV Move Source I:1.0

Dest N10:12

NT8_CONFIGURATION

MOV

MOV Move Source N10:0

-32767<

Dest O:1.0

-32767<

TON

3744<

329<

When CJC check cycle is completed (T1 1:2/DN is set), reset the Checking CJC Bit (B3/100).

0008

0009

REG_CFG_TMR/DN

T11:2

CHECKING_CJC

B3:6

U 4

END

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5-6 Programming Examples

Data Table for Configuration Changes

address 15 data 0 address 15 data 0 N10:0 0000 0010 0010 0011 N10:8 0000 0010 0011 1111 N10:1 0000 0010 0010 0011 N10:2 0000 0010 0010 0011 N10:3 0000 0010 0010 0011 N10:4 0000 0010 0010 0011 N10:5 0000 0010 0010 0011 N10:6 0000 0010 0010 0011 N10:7 0000 0010 0010 0011

Update Time Calculation

Ch 0 Update Time 0.470

Ch 0 Open Circuit Check 0.045

Ch 1 Update Time 0.470

Ch 1 Open Circuit Check 0.045

Ch 2 Update Time 0.470

Ch 3 Update Time 0.470

Ch 3 Open Circuit Check 0.045

Ch 4 Update Time 0.470

Ch 4 Open Circuit Check 0.045

Ch 5 Update Time 0.470

Ch 6 Update Time 0.470

Ch 6 Open Circuit Check 0.045

Ch 7 Update Time 0.470

Ch 7 Open Circuit Check 0.045

CJC Checking 0.290

Update Time 4.410

Auto-calibration Time Calculation

Auto-calibration for 10 Hz 1.975

Auto-calibration for 60 Hz 0.525

Total Auto-calibration 2.500

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Max Time Between Updates 6.910

After a channel configuration word is changed by the ladder logic, the module may not update the processor’s input image until one update time later. In order to ensure that the program is using the proper input data, the ladder logic should wait one update time plus one

Programming Examples 5-7

calibration time to ensure that the new input data matches the channel configuration requested. The above table shows how to calculate the update time and auto-calibration time for the channel configuration being used.

Interfacing to the PID Instruction

The thermocouple module was designed to interface directly to the SLC 5/02 or later processor PID instruction without the need for an intermediate scale operation.

Example - Use 1746-NT8 channel data as the process variable in the PID instruction.

1. Select scaled-for-PID as the data type in the channel

configuration word.

2. Specify the thermocouple channel data word as the process

variable for the PID instruction.

In this example, the value -32701 (8043 H) is the numeric equivalent of configuration word N10:0 for channel 0. It is configured for a type K thermocouple, scaled-for-PID, zero the signal for an open-circuit, 10 Hz, °C, and channel enabled.

Programming for PID Control Example

Initialize NT8 Channel 0

MOV MOVE Source N10:0

-32701

Dest O:3.0

Rung 2:0

First Pass Bit

s:1 ] [ 15

Rung 2:1

Rung 2:2

PID PID Control Block N11:0 Process Variable I:3.0 Control Variable N11:23 Control Block Length 23

SCL SCALE Source N11:23

Rate [/10000]

Offset

Dest

The Rate and Offset parameters should be set per your application. The Destination will typically be an analog output channel.

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5-8 Programming Examples

Monitoring Channel Status Bits

The following example shows how to monitor the open-circuit error bits of each channel and set an alarm in the processor if one of the thermocouples opens. An open-circuit error can occur if the thermocouple breaks, one of the thermocouple wires gets cut or disconnected from the terminal block, or if the CJC sensors are not installed or are damaged.

IMPORTANT

The example shows how to automatically switch between reading the channel status words and channel sensor data words. Specifically, this example shows a simple method of utilizing a timer to periodically switch between reading the channel status and data words.

The program utilizes a timer accumulator value to determine when to set up the configuration words and when to read in the channel status and channel data information. The channel status information is copied from the I:2.0 to I:2.7 registers into registers N7:10 to N7:17. The channel data information is copied from I:2.0 to I:2.7 into registers N7:0 to N7:7. This allows sensor data and channel status information to be accessed at any time from these registers. However, when the module channels are configured to read sensor data, the channel status words (as reflected in N7:10 to N7:17) are not being dynamically updated, and vice-versa.

If a CJC input is not installed or is damaged, all enabled thermocouple alarms are set, and all enabled thermocouple

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Programming Examples 5-9

Monitoring Channel Status Bits Example

During 1st program scan, copy thermocouple channel configuration words (N10:0 - N10:7) to NT8. In addition, initialize channel error registers (N10:20 - N10:27) and Error Flags (B3/119).

#NT8_CH_CNF

0000

0001

S:1

If the NT8 is not checking channel status, store the thermocouple readings in the NT8 last channel reading registers (N10:37). These registers should be used in the remainder of the program (e.g. for temperature control) instead of the NT8 I/O image location.

NT8_CHECKING_STS

B3:6

T11:0 is a repeating 60-second timer which initiates the NT8 channel status check.

NT8_STS_CHECK_TMR/DN

0002

T11:0

NT8_STS_CHECK_TMR

COP

COP Copy File Source #N10:0 Dest #O:1.0 Length 8

#NT8_CH0_STS_FLAGS

FLL

FLL Fill File Source 0 Dest #N10:20 Length 8

CLR

CLR Clear Dest B3:7

0000000000000001<

#NT8_LAST_TEMP_READ

COP

COP Copy File Source #I:1.0 Dest #N10:30 Length 8

TON

TON Timer On Delay Timer T11:0 Time Base 1.0 Preset 60< Accum 10 <

Every 60 seconds, initiate a NT8 channel status check by latching the NTB channel status checking bit and copying the “Status check” configuration words (N10:10 -N10:7) to the NT8 configuration words.

NT8_STS_CHECK_TMR/DN

0003

After copying the “Status Check configuration words” start a 7-second timer (T11:1) to allow the NT8 to update its I/O image to the channel status words. The time required for the NT8 to update its I/O image is dependent on the NT8 configuration. Note, the time required to be greater than the channel update time including the auto calibration time.

NT8_CHECKING_STS

0004

T11:0

B3:6

NT8_CHECKING_STS

#NT8_CH_CNF

COP

COP Copy File Source #N10:10 Dest #O:1.0 Length 8

NT8_STS_CNF_TMR

TON

TON Timer On Delay Timer T11:1 Time Base 1.0 Preset 7< Accum 0<

B3:6

L 4

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5-10 Programming Examples

AFter waiting for the NT8 to update its I/O image, check each channel’s status error bits by masking off the appropriate bits and checking if these bits are set (non-zero). If an error is detected, set the appropriate channel status error bits (B3:112 - B3/119). Rung 5 checks channels 0 to 3).

0005

NT8_STS_CNF_TMR/DN

T11:1

NT8_CHECK_FLAGS

B3:6 OSR

MOV

MOV Move Source 0

Dest B3:7

0000000000000001<

NT8_CH0_STS_FLAGS

MVM

MVM Masked Move Source I:1.0

Mask 0F000h

-4096<

Dest N10:20

4096<

NT8_CH0_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:20

Source B 0

NT8_CH1_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:21

Source B 0

4096<

NT8_CH0_ERROR

B3:7

L 0

NT8_CH1_STS_FLAGS

MVM

MVM Masked Move Source I:1.1

Mask 0F000h

Dest N10:21

NT8_CH2_STS_FLAGS

Masked Move Source I:1.2

Mask 0F000h

Dest N10:22

-4096<

NT8_CH1_ERROR

B3:7

L 1

MVM

-4096<

Publication 1746-UM022B-EN-P - January 2005

Programming Examples 5-11

0006

NT8_CH2_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:22

Source B 0

NT8_CH3_STS_FLAGS

Not Equal Source A N10:23

Source B 0

After waiting for the NT8 to update its I/O image, check each channel’s status error bits by masking off the appropriate bits and checking if these bits are set (non-zero). If an error is detected, set the appropriate channel status error bits

NEQ

NT8_CH2_ERROR

B3:7

L 2

NT8_CH3_STS_FLAGS

MVM

MVM Masked Move Source I:1.3

Mask 0F000h

Dest N10:23

-4096<

NT8_CH3_ERROR

B3:7

L 3

(B3:112 - B3/119). Rung 6 checks channels 4 to 7).

NT8_STS_CNF_TMR/DN

T11:1 B3:6

DN 6

NT8_CHECK_FLAGS2

OSR

NT8_CH4_STS_FLAGS

MVM

MVM Masked Move Source I:1.4

Mask 0F000h

Dest N10:24

-4096<

NT8_CH4_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:24

Source B 0

Publication 1746-UM022B-EN-P - January 2005

NT8_CH4_ERROR

B3:7

L 4

NT8_CH5_STS_FLAGS

MVM

MVM Masked Move Source I:1.5

Mask 0F000h

Dest N10:25

-4096<

5-12 Programming Examples

NT8_CH5_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:25

Source B 0

NT8_CH6_STS_FLAGS

Not Equal Source A N10:26

Source B 0

NEQ

NT8_CH5_ERROR

B3:7

L 5

NT8_CH6_STS_FLAGS

MVM

MVM Masked Move Source I:1.6

Mask 0F000h

Dest N10:26

NT8_CH7_STS_FLAGS

Masked Move Source I:1.7

Mask 0F000h

Dest N10:27

-4096<

NT8_CH6_ERROR

B3:7

L 6

MVM

-4096<

0007

NT8_CH7_STS_FLAGS

NEQ

NEQ Not Equal Source A N10:27

Source B 0

NT8_CH7_ERROR

B3:7

L 7

After updating the error status registers and flags, copy the “regular” NT8 channel configuration words into the NT8 I/O image. Begin 7-second timer to wait for the NT8 to change its I/O image back to the regular channel configuration. Again, the time required by the NT8 I/O image is dependent on the NT8 configuration.

NT8_STS_CNF_TMR/DN

T11:1

#NT8_CH_CNF

COP

COP Copy File Source #N10:0 Dest #O:1.0 Length 8

Publication 1746-UM022B-EN-P - January 2005

Programming Examples 5-13

NT8_REG_CNF_TMR

TON

TON Timer On Delay Timer T11:2 Time Base 1.0 Preset 7< Accum 0<

After the NT8 has restored its normal I/O image, clear the NT8 checking status bit (B3/100).

NT8_REG_CNF_TMR/DN

0008

0009

PLC 5 Example with NT8 in Remote I/O Rack

NT8_CHECKING_STS

T11:2

B3:6

END

The following example shows sample ladder logic when using a PLC/5 controller to control the module in remote rack across the Remote I/O network. The PLC/5 must use Block transfer reads and writes to communicate with the 1746-NT8 module in a remote rack. Note, the example provides code which will reconfigure the module if the PLC/5 senses are remote rack fault. Also, the PLC/5 processor uses the exact same configuration words as the SLC 500 processors.

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5-14 Programming Examples

During the first scan, clear the NT8 Configurated bit (B3/4) to initiate the NT8 configuration process. First scan or SFC

step

S:1

If the NT8 is configured and a rack fault occurs, clear the NT8 Configured bit (B3/4) to initiate the NT8 configuration process.

NT8_CONFIGURED

B3:0

RIO_RACK1_FLT

NEQ

NEQ Not Equal Source A N11:3

Source B 0

Until the NT8 is configured, send the 8 configuration words (N12:10 - 17) to the NT8 using repeating BTW’s.

NT8_CONFIGURED

B3:0

When the NT8 is configured latch the NT8 Configured bit (B3/4).

NT8_BTW/EN

BT20:1

NT8_BTW

BTW

BTW Block Transfer Write Module Type Rack 001 Group 0 Module 0 Control Block BT20:1 Data File N12:10 Length 8 Continuous No

RIO_RACK1_FLT

Masked Move Source N30:2

Mask 0FH

Dest N11:3

Generic Block Transfer

NT8_CONFIGURED

B3:0

U 4

MVM

256<

15<

NT8_CONFIGURED

B3:0

U 4

BTW_DONE

BT20:1

If the NT8 is configured, read the 8 input words into N12:0 - N12:7 using repeating BTR’s.

NT8_CONFIGURED

Publication 1746-UM022B-EN-P - January 2005

B3:0

BTR_TRIGGER

BT20:0

NT8_CONFIGURED

BTR

BTR Block Transfer Read Module Type Rack 001 Group 0 Module 0 Control Block BT20:0 Data File N12:0 Length 8 Continuous No

Generic Block Transfer

B3:0

L 4

END

Programming Examples 5-15

SLC 500 Example with NT8 in Remote I/O Rack

The following example shows sample ladder logic when using an SLC controller to control the module in remote rack across the Remote I/O network. The SLC must use Block transfer reads and writes to communicate with the 1746-NT8 module in a remote rack.

RIO example with SLC processor

SLC processors with a 1747-SN series B RIO Scanner can use the block transfer instructions similarly to the PLC/5. This ladder example shows this implementation. The data file elements N20:10- N20:17 contain the configuration data for the NT8 as defined in previous examples.

Publication 1746-UM022B-EN-P - January 2005

5-16 Programming Examples

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Chapter

Troubleshooting Your Module

This chapter describes troubleshooting with channel-status and module-status LEDs. It explains the types of conditions that might cause the module to flag an error and suggests what corrective action you could take. Topics include:

• module and channel diagnostics

• LED indicators

• interpreting I/O error codes

• troubleshooting flowchart

Module and Channel Diagnostics

The module operates at two levels:

• module level

• channel level

Module-level operation includes functions such as powerup, configuration, and communication with the SLC processor. Channel level operation includes functions such as data conversion and open circuit detection. The module performs internal diagnostics at both levels and immediately indicates detected error conditions with either of its status LEDs. See the LED troubleshooting tables on page 6-3 for LED operation.

Module Diagnostics at Powerup

At module powerup, the module performs a series of internal diagnostic tests. If the module detects a failure, the module status LED remains off.

Channel Diagnostics

When a channel is enabled, the module checks for a valid configuration. Then on each scan of its inputs, the module checks for out-of-range and open-circuit fault conditions of its inputs including the CJC input.

When the module detects a failure of any channel diagnostic test, it causes the channel status LED to blink and sets the corresponding

1 Publication 1746-UM022B-EN-P - January 2005

6-2 Troubleshooting Your Module

channel fault bit (bits 12-15 of the channel status word). Channel fault bits and LEDs are self-clearing when fault conditions are corrected.

IMPORTANT

If you clear the channel enable bit, the channel status bits are reset.

The module has nine LEDs; as shown below.

• eight channel-status LEDs, numbered to correspond with each

channel

• one module-status LED

INPUT

LEDs for Channels 0 to 7

LED for Module Status

Channel Status

Module

Thermocouple/mV

Publication 1746-UM022B-EN-P - January 2005

LED Troubleshooting Tables

Module-status LED

Troubleshooting Your Module 6-3

If Module Status LED is:

On The module is

Off The module is

Flashing Jumper may be in

Module-status and Channel-status LED

If Module Status LED is:

And Channel Status LED is:

On The channel is enabled. No action required.

Flashing The module detected:

Then:

operating properly.

turned off, or it detected a module fault.

wrong position.

Then: Take this Corrective Action:

open-circuit condition, under-range condition, over-range condition.

Take this Corrective Action:

No action required.

Cycle power. If the condition persists, call your local Allen-Bradley distributor for assistance.

Check jumper 1 position.

Examine error bits in status word If bit 12=1, the input has an open circuit If bit 13=1, the input value is under range If bit 14=1, the input value is over range If bit 15=1, the channel has a diagnostic channel error

Off The module is in power

up, or the channel is disabled.

Publication 1746-UM022B-EN-P - January 2005

No action is required.

6-4 Troubleshooting Your Module

Channel-status LEDs (Green)

The channel-status LED operates with status bits in the channel status word to indicate the following faults detected by the module:

• invalid channel configuration

• an open-circuit input

• out-of-range errors

• selected filter frequency data acquisition or auto-calibration

errors

When the module detects any of the following fault conditions, it causes the channel-status LED to flash and sets the corresponding fault bit in the channel status word. Channel fault bits (bits 12 through

15) and channel-status LEDs are self-clearing when fault conditions are corrected.

Open-circuit Detection (Bit 12)

If open-circuit detection is enabled for an input channel, the module tests the channel for an open-circuit condition each time it scans its input. Open-circuit detection is always performed for the CJC inputs. Possible causes of an open circuit include:

• broken thermocouple or CJC sensor

• thermocouple or CJC sensor wire cut or disconnected

• millivolt input wire cut or disconnected

Out-of-Range Detection (Bit 13 for Under Range, Bit 14 for Over Range)

The module tests all enabled channels for an out-of-range condition each time it scans its inputs. Possible causes of an out-of-range condition include:

• the temperature is too hot or too cold for the thermocouple

being used.

• a type B thermocouple may be registering a °F value in

Engineering Units x1 beyond the range allowed by the SLC processor (beyond 32,767) for the data word.

• a CJC sensor may be damaged or the temperature being

detected by the CJC may be outside the CJC sensor range limits.

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Troubleshooting Your Module 6-5

Channel Error (Bit 15)

The module sets this fault bit when it detects any of the following configuration errors:

• configuration bits 1 through 4: invalid input type = 1010, 1011,

1100, 1101, or 1110.

• configuration bits 12 through 14: invalid non-zero bit setting.

• invalid data acquisition of an input channel.

• the filter frequency selected for the valid channel currently fails

auto-calibration range checks.

Module Status LED (Green)

The module-status LED indicates when the module detects a non-recoverable fault at power up or during operation. For this type of fault, the module:

Interpreting I/O Error Codes

• no longer communicates with the SLC processor

• disables all channels

• clears all data and status words

A module failure is non-recoverable and requires the assistance of your local Allen-Bradley distributor.

I/O error codes appear in word S:6 of the SLC processor status file. The first two digits of the error code identify the slot (in hexadecimal) with the error. The last two digits identify the I/O error code (in hexadecimal).

The error codes that apply to your module include (in hexadecimal):

• 50 through 5E

• 71 (watchdog error)

• 90 through 94

For a description of the error codes, refer to the SLC 500 Instruction Set Reference Manual, publication 1746-RM001.

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6-6 Troubleshooting Your Module

Troubleshooting Flowchart

Check LEDs on module.

Module Status

LED(s) off.

Module fault

condition.

Check to see that module is seated

properly in

chassis. Cycle

power.

Is problem corrected?

Contact your local

Allen-Bradley

distributor.

Module Status

LED(s) off.

Normal module

operation.

End.

Ye s

faulted channel(s) configured for mV

or thermocouple

Thermocou ple

Check that wiring is secure

at both CJCs and that the

temperature within the enclosure is in the range limits of the CJC sensor.

End .

Ye s

Contact your local

Fault

condition.

Are

input?

Is more than

one LED

blinking?

Ye s

CJC fault has

probably

occurred.

Is problem corrected?

Allen-Bradley

distributor.

Channel

Status LED(s)

flashing.

Check channel

status words bits

12 through 15.

Bit 15

set 1

Bit 14

set (1)

Bit 13

set (1)

Bit 12

set (1)

Channel

Status LED(s)

off.

Channel

is not enabled.

Enable channel if

desired by setting

channel config.

word (bit 0=1).

Retry.

Channel error. Check

configuration word bits 1

through 4 for valid input

type configuration and

ensure bits 12 through 14

are set to zero. Retry.

Over-range condition exists.

The input signal is greater

thank the high scale limit for

the channel or the CJC

connections. Corret and

retry.

Under-range condition

exists. The input signal is

less than the low scale limit

for the channel or the CJC

connections. Correct and

retry.

An open-circuit condition

is present. Check channel

and CJC wiring for open or

loose connections. Retry.

Channel

Status LED(s)

on.

Channel

is enabled and

working.

End.

Ye s

Is problem corrected?

Contact your local

Allen-Bradley

distributor.

Publication 1746-UM022B-EN-P - January 2005

Chapter

Maintaining Your Module And Safety Considerations

Read this chapter to familiarize yourself with:

• preventive maintenance

• safety considerations

The National Fire Protection Association (NFPA) recommends maintenance procedures for electrical equipment. Refer to article 70B of the NFPA for general safety-related work practices.

Preventive Maintenance

Safety Considerations

The printed circuit boards of your module must be protected from dirt, oil, moisture, and other airborne contaminants. To protect these boards, install the SLC 500 system in an enclosure suitable for its operating environment. Keep the interior of the enclosure clean, and whenever possible, keep the enclosure door closed.

Also, regularly inspect the terminal connections for tightness. Loose connections may cause a malfunction of the SLC system or damage to the components.

ATTENTION

Safety is always the most important consideration. Actively think about the safety of yourself and others, as well as the condition of your equipment. Consider the following:

Possible Loose Connections

Before inspecting connections, always ensure that incoming power is OFF.

Failure to observe this precaution can cause personal injury and equipment damage.

Indicator Lights – When the module status LED on your module is illuminated, your module is receiving power.

Activate Devices When Troubleshooting – Never reach into a machine to activate a device; the machine may move unexpectedly. Use a wooden stick.

1 Publication 1746-UM022B-EN-P - January 2005

7-2 Maintaining Your Module And Safety Considerations

Stand Clear Of Machinery – When troubleshooting a problem with any SLC 500 system, have all personnel remain clear of machinery. The problem may be intermittent, and the machine may move unexpectedly. Have someone ready to operate an emergency stop switch.

ATTENTION

Possible Equipment Operation

Never reach into a machine to actuate a switch. Also, remove all electrical power at the main power disconnect switches before checking electrical connections or inputs/outputs causing machine motion.

Failure to observe these precautions can cause personal injury or equipment damage.

Safety Circuits – Circuits installed on machinery for safety reasons (like over-travel limit switches, stop push-buttons, and interlocks) should always be hard-wired to the master control relay. These circuits should also be wired in series so that when any one circuit opens, the master control relay is de-energized, thereby removing power.

Class 1, Division 2 - This equipment is suitable for use in Class 1, Division 2, groups A, B, C, and D or non-hazardous locations only.

ATTENTION

Explosion Hazard

Never modify these circuits to defeat their function. Serious injury or equipment damage may result.

Publication 1746-UM022B-EN-P - January 2005

• Substitution of components may impair suitability

for Class 1 Division 2.

• Do not disconnect equipment unless power has

been switched off or the area is known to be nonhazardous.

• When in hazardous locations, turn off power

before replacing or wiring modules.

Refer to your system’s User Manual for more information.

Electrical Specifications

Appendix

Module Specifications

This appendix lists the specifications for the 1746-NT8 Thermocouple/millivolt Input Module.

Backplane Current Consumption 120 mA at 5V dc

70 mA at 24Vdc

Backplane Power Consumption 2.28W maximum (0.6W at 5V dc, 1.68W at 24V dc)

Number of Channels 8 (backplane and channel-to-channel isolated)

I/O Chassis Location Any I/O module slot except 0

A/D Conversion Method Sigma-Delta Modulation

Input Filtering Input Filtering Low pass digital filter with

programmable notch (filter) frequencies

Normal Mode Rejection (between [+] input and [-] input)

Greater than 100 dB at 50/60 Hz

Common Mode Rejection (between input and ground)

Input Filter Cut-Off Frequencies

•2.6 Hz at 10 Hz filter frequency

•13.1 Hz at 50 Hz filter frequency

•15.72 Hz at 60 Hz filter frequency

•65.5 Hz at 250 Hz filter frequency

Calibration Module autocalibrates at power-up and

Input Over-voltage Protection ±30V dc continuous 600W pulsed for 1 ms.

Isolation 500V dc for 1 minute between inputs and chassis

Greater than 100 dB at 50/60 Hz

approximately every two minutes afterward

ground and between inputs and backplane. 12.5V dc continuous between channels.

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A-2 Module Specifications

Physical Specifications

LED Indicators 9 green status indicators, one for each of 8 channels and

one for module status

Module ID Code

Recommended Cable: for thermocouple inputs…

3533

Appropriate shielded twisted pair thermocouple extension wire

(1)

Environmental Specifications

for mV inputs…

Maximum Wire Size One 14 AWG wire or two 22 AWG wires per terminal

(1) Refer to the thermocouple manufacturer for the correct extension wire.

Operating Temperature 0°C to +60°C (+32°F to +140°F)

Storage Temperature -40°C to +85°C (-40°F to +185°F)

Relative Humidity 5% to 95% (without condensation)

Certification UL and CUL approved

Hazardous Environment Classification Class I Division 2 Hazardous Environment

EMC CE compliant for all applicable directives

Belden™ 8761 or equivalent

Groups A, B, C, D

C-Tick compliant for all applicable acts

Publication 1746-UM022B-EN-P - January 2005

Input Specifications

Type of Input (Selectable)

Thermocouple Linearization NIST ITS-90 standard

Cold Junction Compensation Accuracy ±1.72°C, -25°C to +105°C

Module Input Impedance Greater than 10MW

Input Device Impedance Output impedance of input device must be less than 100 ohm to meet

Temperature Scale (Selectable) °C or °F and 0.1°C or 0.1°F

DC Millivolt Scale (Selectable) 0.1 mV or 0.01 mV

Module Specifications A-3

Thermocouple Type J -210°C to +760°C (-346°F to +1400°F)

Thermocouple Type K -270°C to +1370°C (-454°F to +2498°F)

Thermocouple Type T -270°C to +400°C (-454°F to +752°F)

Thermocouple Type E -270°C to +1000°C (-454°F to +1832°F)

Thermocouple Type R 0°C to +1768°C (+32°F to +3214°F)

Thermocouple Type S 0°C to +1768°C (+32°F to +3214°F)

Thermocouple Type B +300°C to +1820°C (+572°F to +3308°F)

Thermocouple Type N 0°C to +1300°C (+32°F to +2372°F)

Millivolt (-50mV dc to +50mV dc)

Millivolt (-100mV dc to +100mV dc)

accuracy specifications.

Open Circuit Detection (Selectable) Upscale, Downscale, Zero, or Disabled

Time to Detect Open Circuit One channel cycle time

Input Step Response 0 to 95% in 400 ms (10 Hz)

Display Resolution See Channel Data Word Resolution table on page 4-8

Overall Module Accuracy at 257°C (77°F) See Module Accuracy Tables, page A-6

Overall Module Accuracy See Module Accuracy Tables, page A-6

Overall Module Drift See Module Accuracy Tables, page A-6

Module Update Time Dependent upon enabled channels (see Update Time, page 3-7)

Channel Turn-Off Time Up to one module update time

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A-4 Module Specifications

Overall Accuracy

The accuracy of the module is determined by many aspects of the hardware and software functionality of the module. The following discussion explains what the user can expect in terms of accuracy based on the thermocouple and millivolt inputs for the 1746-NT8 module.

The accuracies specified as follows include errors due to the cold junction compensation for thermocouples and hardware and software errors associated with the system. The hardware and software errors include calibration of the system and non-linearity of the ADC. For the sake of the calculations, the resolution of the ADC was assumed to be at least 16 bits (use of the 10 Hz, 50 Hz, and 60 Hz filter frequencies).

TIP

The 250 Hz frequency should not be applied to thermocouple inputs (See table on page 3-4).

Millivolt

For millivolt inputs, the error is ±30 uV typical at 25°C, and ±120 uV maximum over temperature for the 10 Hz, 50 Hz, and 60 Hz filter frequencies. The 250 Hz filter frequency accuracy is highly dependent upon operating environment and may be worse in noisy environments.

As with any high precision analog input device, system grounding does affect the accuracy of the readings. Care should be taken to ensure that the proper filter frequency has been selected based on the environmental conditions in which the module is to be used.

CJC compensation does not affect the millivolt inputs in terms of accuracy.

The following diagrams are provided to give a measure of “system” accuracy using test data from a single test module. The tests recorded deviation between measured and expected values. This data was taken over an entire range of the thermocouple (or millivolt range, as applicable) and over the module’s temperature range (0 - 60°C). The maximum deviation for each thermocouple temperature (or millivolt range) was plotted.

Publication 1746-UM022B-EN-P - January 2005

50.00

45.00

40.00

35.00

30.00

Module Specifications A-5

uV Err, ±100mV Span, Prop Cts, 60 Hz, 0°C

25.00

20.00

uV Deviation

15.00

10.00

5.00

0.00

-100

-99.92

50.00

45.00

40.00

35.00

30.00

25.00

20.00

-0.1

0.06

-99.84

-99.76

-99.68

-99.6

-99.52

-50.16

-50.08

-0.18

-50

-49.92

-49.84

-0.02

0.14

mV Input

uV Err, ±100mV Span, Prop Cts, 60 Hz, 25°C

49.8

49.88

49.96

50.04

50.12

50.2

99.56

99.64

99.72

99.8

99.88

uV Error

99.96

uV Error

15.00

uV Deviation

10.00

5.00

0.00

-100

-99.92

-99.84

-99.76

-99.68

-99.6

-99.52

-50.16

-50.08

-50

-49.92

-49.84

-0.1

-0.18

-0.02

mV Input

0.06

0.14

49.8

49.88

49.96

50.04

50.12

50.2

99.56

99.64

99.72

99.8

99.88

99.96

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A-6 Module Specifications

uV Err, ±100mV Span, Prop Cts, 60 Hz, 60°C

90.00

80.00

70.00

60.00

50.00

40.00

30.00

uV Deviation

20.00

10.00

0.00

-100

-99.92

-99.84

-99.76

-99.68

-99.6

-99.52

-50.16

-50.08

-50

-49.92

-49.84

-0.18

-0.1

-0.02

0.06

0.14

49.8

49.88

49.96

50.04

50.12

50.2

99.56

99.64

99.72

99.8

99.88

99.96

mV Input

uV Error

Thermocouple

The following table provides the total error expected of the thermocouple based on the thermocouple type, and the given reference point, at 25°C. The calculations assumed typical hardware/software error and typical CJC accuracy at 25°C.

Thermocouple Type Thermocouple Reference Point Error

J +275°C (+527°F) ±1.4°C (±2.52°F)

K +550°C (+1022°F) ±1.5°C (±2.7°F)

T +65°C (+149°F) ±1.3°C (±2.34°F)

E +365°C (+689°F) ±1.3°C (±2.34°F)

R +885°C (+1625°F) ±3.6°C (±6.48°F)

S +885°C (+1625°F) ±3.4°C (±6.12°F)

B +1060°C (+1940°F) ±2.7°C (±4.86°F)

N +500°C (+932°F) ±1.3°C (±2.34°F)

The following table provides the total error expected over the temperature range of the module (0 to 60°C) for each thermocouple based upon the type, and the given reference point, at the extremes of the temperature range (0 or 60°C). The calculations are based on maximum hardware/software error and maximum CJC inaccuracy over temperature.

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Module Specifications A-7

Thermocouple Type Thermocouple Reference Point Error

J +275°C (+527°F) ±3.0°C (±5.4°F)

K +550°C (+1022°F) ±3.0°C (±5.4°F)

T +65°C (+149°F) ±3.4°C (±6.12°F)

E +365°C (+689°F) ±2.5°C (±4.5°F)

R +885°C (+1625°F) ±6.5°C (±11.7°F)

S +885°C (+1625°F) ±7.2°C (±12.96°F)

B +1060°C (+1940°F) ±8.4°C (±15.12°F)

N +500°C (+932°F) ±3.0°C (±5.4°F)

The diagrams that follow for each thermocouple type give data for a sample module over the input range of the thermocouple over temperature. Thermocouples are usually parabolic in their µV to °C curves. Normally, at the ends of any given thermocouple range, the ratio of change in temperature increases as a result of a change in voltage. In other words, at the ends, a smaller change in voltage results in a larger change in °C. The data that follows gives an idea of a sample module’s error over the thermocouple range, versus at a single reference point as provided with the tables above.

TIP

The data was recorded at 60 Hz. Values at 10 Hz and 50 Hz would be comparable.

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A-8 Module Specifications

uV Err, ±100mV Span, Prop Cts, 60 Hz, 0°C, 25°C, 60°C

100 mV Deviation Over Temp

0.06

0.04

0.02

-0.02

-0.04

Deviation Voltage (mV)

-0.06

-0.08

-40000 -20000 0 20000 40000

-0.1 Input Voltage (counts)

uV Err, ±50mV Span, Prop Cts, 60 Hz, 25°C

50 mV Deviation Over Temp

0.03

0.02

0.01

Delta 60˚C

Delta 25˚C

Delta 0˚C

Delta 25˚C

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-0.01

Deviation Voltage (mV)

-0.02

-0.03

4000020000-20000-40000 0

Input Voltage (counts)

Module Specifications A-9

Thermocouple J Deviations Over Temperature

Delta 60˚C

Delta 25˚C

-1

Degrees C Deviation

-2

-400 -200 0 200 400 600 800 1000

Degrees C TC Input

Thermocouple K Deviations Over Temperature

-2

-4

-6

Degrees C Deviation

-8

Delta 0˚C

Delta 60˚C Delta 25˚C Delta 0˚C

-10

-12

-500 0 500 1000 1500

Degrees C TC Input

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A-10 Module Specifications

Thermocouple T Deviations Over Temperature

-400 -200 0 200 400 600

-2

-4

-6

-8

Degrees C Deviation

-10

Delta 60˚C

Delta 25˚C Delta 0˚C

-12

Thermocouple E Deviations Over Temperature

Degrees C TC Input

-400 -200 0 200 400 600 800 1000 1200

-1

-2

-3

-4

Degrees C Deviation

-5

-6 Degrees C TC Input

Delta 60˚C Delta 25˚C Delta 0˚C

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Thermocouple B Deviations Over Temperature

300 800 1300 1800

-1

-2

Module Specifications A-11

-3

-4

-5

Degrees C Deviation

-6

-7

Thermocouple N Deviations Over Temperature

2.5

1.5

0.5

Degrees C TC Input

0 200 400 600 800 1000 1200 1400

Delta 60˚C

Delta 25˚C Delta 0˚C

Delta 60˚C

Delta 25˚C

Delta 0˚C

-0.5

Degrees C Deviation

-1

-1.5

Degrees C TC Input

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A-12 Module Specifications

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Appendix

Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples

This appendix describes the types of thermocouples available and explains the trade-offs in using them with the 1746-NT8 module.

Thermocouple Types

There are three (3) types of thermocouple junctions:

• Grounded Junction - The measuring junction is physically

connected to the protective sheath forming a completely sealed integral junction. If the sheath is metal (or electrically conductive), then there is electrical continuity between the junction and sheath. The junction is protected from corrosive or erosive conditions. The response time approaches that of the exposed junction type.

• Ungrounded Junction - The measuring junction is electrically

isolated from the protective metal sheath. This may also be referred to as an insulated junction. This type is often used where noise would affect the reading and for frequent or rapid temperature cycling. The response time is longer than the grounded junction.

• Exposed Junction - The measuring junction does not have a

protective metal sheath, so it is exposed. This junction style provides the fastest response time but leaves the thermocouple wires unprotected against corrosive or mechanical damage.

The following illustrations show each of the three (3) thermocouple types.

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B-2 Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples

Grounded Junction

Metal Sheath

Extension Wire

Ungrounded (Insulated) Junction

Measuring Junction is connected to sheath

Measuring Junction is isolated from sheath

Isolation

Exposed Junction

Measuring Junction has no sheath

The 1746-NT8 module provides the following electrical isolation:

• 12.5V dc electrical isolation channel-to-channel

• 500V dc electrical isolation channel-to-chassis ground

• 500V dc electrical isolation channel-to-backplane

Care must be taken when choosing a thermocouple type and connecting it to the 1746-NT8 module from the environment being measured. If adequate precautions are not taken for a given thermocouple type, the electrical isolation of the 1746-NT8 module may be compromised.

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Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples B-3

Grounded Junction

As shown in the following illustration, the shield input terminals are internally connected together, which are then connected to chassis ground. Using grounded junction thermocouples with electrically conductive sheaths removes the thermocouple signal to chassis ground isolation of the module. This is inherent to the thermocouple construction. In addition, if multiple grounded junction thermocouples are used, the module’s channel-to-channel isolation is removed since there is no isolation between signal and sheath and the sheaths are tied together. It should be noted that the isolation is removed even if the sheaths are connected to chassis ground at a location other than the module, since the module is connected to chassis ground.

CH0

CH3

1746-NT8

MUXES

Grounded junction with nonconductive protective sheath

Metal sheath with electrical continuity to thermocouple signal wires. (floating ground connection)

For grounded junction thermocouples, it is recommended that they have protective sheaths made of electrically insulated material (e.g. ceramic), or the metal protective sheaths be floated. The metal sheaths would need to be floated with respect to any path to chassis ground or to another thermocouple metal sheath. This means the metal sheath must be insulated from electrically conductive process material and have all connections to chassis ground broken. It should be noted that a floated sheath may result in a less noise immune thermocouple signal.

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B-4 Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples

Exposed Junction Thermocouples

Recommended wiring for exposed junction thermocouples is shown in the following illustration. Using exposed junction thermocouples may result in removal of channel-to-channel isolation. This may occur if multiple exposed thermocouples are in direct contact with electrically conductive process material. To prevent violation of channel-to-channel isolation:

• For multiple exposed thermocouples, do not allow the

measuring junction of the thermocouple to make direct contact with electrically conductive process material.

• Use all ungrounded junction thermocouple instead of the

exposed junction type.

Grounded junction with nonconductive protective sheath

Metal sheath with electrical continuity to thermocouple signal wires. (floating ground connection)

CH0

CH3

1746-NT8

MUXES

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Appendix

Configuring the 1746-NT8 Module with RSLogix 500

This appendix describes how to configure the NT8 module with RSLogix 500 v6.10 or higher. To configure your module:

1. Access the I/O Configuration menu.

2. Determine the chassis number and slot location of where the

NT8 module is located. Highlight the module.

I/O configuration menu

3. Press the Adv. Config button.

The following dialog box appears.

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C-2 Configuring the 1746-NT8 Module with RSLogix 500

Adv. Configuration menu

4. Press the Configure button.

The following dialog box appears. This allows you to configure options for each channel.

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Module configuration Options

Configuring the 1746-NT8 Module with RSLogix 500 C-3

The dialog box allows you to access the parameters for all channels. Each tab has an identical menu with the parameters shown.

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C-4 Configuring the 1746-NT8 Module with RSLogix 500

Menu Options

Opening the drop down menus of the various parameters shows the available choices. The following summarizes the different options for each parameter.

Parameter Description

Channel Enabled

Input Type

Controls bit 0 of the configuration file and sets whether the channel is being used.

Sets bits 1 to 4 and sets the type of thermocouple being used.

Temperature Units

Filter Frequency

Broken Input

Sets bit 9 for temperature (°C or °F).

Sets bits 10 and 11 and determine the frequency of the channel filter.

Sets bits 7 and 8 and determines how to handle an open circuit condition.

Data Format

Input Image Type

Sets bits 5 and 6 and determines the scale of the data.

Sets the input to status word or data word and sets bit 15.

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Rockwell Automation 1746-NT8 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Important User Information

Table of Contents

Summary of Changes

Preface

Who Should Use This Manual

What This Manual Covers

Related Documentation

Common Techniques Used in this Manual

Module Overview

General Description

System Overview

Installing And Wiring Your Module

Electrostatic Damage

Power Requirements

General Considerations

Module Installation and Removal

Wiring Your Module

Module ID Code

Module Addressing

Channel Filter Frequency Selection

Update Time

Channel Turn-On, Turn-Off, and Reconfiguration Times

Auto-calibration

Response to Slot Disabling

Channel Configuration, Data, and Status

Channel Configuration

Channel Configuration Procedure

Scaling Examples

Channel Data/Status Word

Channel Status Checking

Programming Examples

Automatic Monitoring Thermocouples and CJC Sensors

Verifying Configuration Changes

Interfacing to the PID Instruction

Monitoring Channel Status Bits

PLC 5 Example with NT8 in Remote I/O Rack

SLC 500 Example with NT8 in Remote I/O Rack

Troubleshooting Your Module

Module and Channel Diagnostics

Interpreting I/O Error Codes

Maintaining Your Module And Safety Considerations

Preventive Maintenance

Safety Considerations

Electrical Specifications

Module Specifications

Physical Specifications

Environmental Specifications

Input Specifications

Using Grounded Junction, Ungrounded Junction, and Exposed Junction Thermocouples

Thermocouple Types

Isolation

Configuring the 1746-NT8 Module with RSLogix 500