Allen-Bradley Thermocouple/ Millivolt Input Module (Cat. No.
Important User Information Because of the variety of uses for the products described in this publication, those responsible for the application and use of this control equipment must satisfy themselves that all necessary steps have been taken to assure that each application and use meets all performance and safety requirements, including any applicable laws, regulations, codes and standards. The illustrations, charts, sample programs and layout examples shown in this guide are intended solely for example.
The information below summarizes the changes to the company-wide templates since the last release. New Information The following new information has been added to this manual: • the “L” type thermocouple selection has been added for use in some European markets. Updated Information Calibration procedures have been revised to eliminate 1 method in order to better control calibration results.
soc–ii Summary of Changes Publication 1794-6.5.
Table of Contents Overview of Flex I/O and your Thermocouple/mV Module How to Install Your Thermocouple/mV Input Module Module Programming Chapter 1 Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The FLEX I/O System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How FLEX I/O Analog Modules Communicate with Programmable Controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii Table of Contents Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Calibrating Your Module Chapter 4 Chapter Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Configuring Your Thermocouple/mV Module . . . . . . . . . . . . . . . . . Range Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Input Scaling . . . . . . .
Table of Contents Calibrating Your Thermocouple/mV Module using DeviceNetManager Software (Cat. No. 1787-MGR) . . . . . . . . . . . . . . . . . . . . . . . . Offset Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gain Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specifications 6–9 6–9 6–11 Appendix A Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Derating Curve . . . . . . . . . . . . .
iv Table of Contents Publication 1794-6.5.
Preface Using This Manual Preface Objectives Read this preface to familiarize yourself with this manual and to learn how to use it properly and efficiently. Audience We assume that you have previously used an Allen-Bradley programmable controller, that you are familiar with its features, and that you are familiar with the terminology we use. If not, read the user manual for your processor before reading this manual.
P–2 Using This Manual Conventions We use these conventions in this manual: In this manual, we show: Like this: that there is more information about a topic in another chapter in this manual that there is more information about the topic in another manual For Additional Information For additional information on FLEX I/O systems and modules, refer to the following documents: Publications Catalog Number 1787-MGR Publication 1794-6.5.
Chapter 1 Overview of FLEX I/O and your Thermocouple/mV Module Chapter Objectives In this chapter, we tell you: • what the FLEX I/O system is and what it contains • how FLEX I/O modules communicate with programmable controllers • the features of your thermocouple module The FLEX I/O System Adapter/Power Supply FLEX I/O is a small, modular I/O system for distributed applications that performs all of the functions of rack-based I/O.
1–2 Overview of FLEX I/O and your Thermocouple/mV Module The adapter/power supply transfers data to the module (block transfer write) and from the module (block transfer read) using BTW and BTR instructions in your ladder diagram program. These instructions let the adapter obtain input or output values and status from the module, and let you establish the module’s mode of operation. The illustration describes the communication process.
Overview of FLEX I/O and your Thermocouple/mV Module Features of your Modules 1–3 The module label identifies the keyswitch position, wiring and module type. A removable label provides space for writing individual designations per your application.
1–4 Overview of FLEX I/O and your Thermocouple/mV Module Publication 1794-6.5.
Chapter 2 How to Install Your Thermocouple/mV Input Module In this chapter, we tell you: • • • • Before You Install Your Input Module how to install your module how to set the module keyswitch how to wire the terminal base about the indicators Before installing your thermocouple/mV module in the I/O chassis: You need to: As described under: Calculate the power requirements of all modules in each chassis.
2–2 How to Install Your Thermocouple/mV Input Module Low Voltage Directive This product is tested to meet Council Directive 73/23/EEC Low Voltage, by applying the safety requirements of EN 61131–2 Programmable Controllers, Part 2 – Equipment Requirements and Tests.
How to Install Your Thermocouple/mV Input Module 2–3 Methods of wiring the terminal base units are shown in the illustration below. Wiring the Terminal Base Units (1794-TB2 and -TB3 shown) ! ATTENTION: Do not daisy chain power or ground from the thermocouple terminal base unit to any ac or dc discrete module terminal base unit.
2–4 How to Install Your Thermocouple/mV Input Module Installing the Module The thermocouple/mV module mounts on a 1794-TB2, -TB3 or -TB3T terminal base unit. Important: You must use a 1794-TB3T terminal base unit if you are using the thermocouple/mV module for thermocouple inputs. You can use the 1794-TB2 or -TB3 terminal base for millivolt inputs only. 7 3 1 2 6 4 5 1. Rotate the keyswitch (1) on the terminal base unit (2) clockwise to position 3 as required for the thermocouple/mV module. 2.
How to Install Your Thermocouple/mV Input Module Connecting Wiring for the Thermocouple/mV Module 2–5 Thermocouple/mV module wiring is made through the terminal base unit on which the module mounts. The module comes with 2 cold junction compensators for use when using the thermocouple module in the thermocouple mode.
2–6 How to Install Your Thermocouple/mV Input Module ATTENTION: The Thermocouple/mV module does not receive power from the backplane. +24V dc power must be applied to your module before installation. If power is not applied, the module position will appear to the adapter as an empty slot in your chassis. ! 4. On 1794-TB3T terminal base units: Connect the cold junction compensation (CJC) wiring to terminals 36, 37 and 38 for inputs 0 through 3, and terminals 47, 48 and 49 for inputs 4 through 7.
How to Install Your Thermocouple/mV Input Module 2–7 ATTENTION: The thermocouple/mV modules do not receive power from the backplane. +24V dc power must be applied to your module before operation. If power is not applied, the module position will appear to the adapter as an empty slot in your chassis. If the adapter does not recognize your module after installation is completed, cycle power to the adapter. ! ATTENTION: Total current draw through the terminal base unit is limited to 10A.
2–8 How to Install Your Thermocouple/mV Input Module Module Indicators The thermocouple/mV module has one status indicator that is on when power is applied to the module.
Chapter Chapter Objectives 3 In this chapter, we tell you about: • block transfer programming • sample programs for the PLC-3 and PLC-5 processors Block Transfer Programming Your thermocouple/mV module communicates with the processor through bidirectional block transfers. This is the sequential operation of both read and write block transfer instructions.
3–2 Module Programming Sample programs for FLEX I/O Analog Modules The following sample programs show you how to use your analog module efficiently when operating with a programmable controller. These programs show you how to: • configure the module • read data from the module These example programs illustrate the minimum programming required for communication to take place.
Module Programming 3–3 PLC-5 Programming The PLC-5 program is very similar to the PLC-3 program with the following exceptions: 1. Block transfer enable bits are used instead of done bits as the conditions on each rung. 2. Separate block transfer control files are used for the block transfer instructions. Figure 3.
3–4 Module Programming PLC-2 Programming The 1794 analog I/O modules are not recommended for use with PLC-2 family programmable controllers due to the number of digits needed for high resolution. Chapter Summary Publication 1794-6.5.7 In this chapter, you learned how to program your programmable controller. You were given sample programs for your PLC-3 and PLC-5 family processors.
Chapter 4 Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Chapter Objectives In this chapter, we tell you about: • • • • Configuring Your Thermocouple/mV Module configuring your module’s features entering your data reading data from your module the read block format Because of the wide variety of possible configurations, you must configure your module to conform to the specific application that you have chosen.
4–2 Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Range Selection Individual input channels are configurable to operate with the following sensor types: Sensor Type Range Voltage Millivolt –76.50 to +76.
Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter 4–3 You select input scaling using the designated words of the write block transfer instruction. Refer to the Bit/Word description for write word 0, bits 00 and 01. Hardware First Notch Filter A hardware filter in the analog to digital converter lets you select a frequency for the first notch of the filter. Selection of the filter influences the analog to digital output data rate and changes the module throughput.
4–4 Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Reading Data From Your Module Read programming moves status and data from the thermocouple input module to the processor’s data table. The processor’s user program initiates the request to transfer data from the thermocouple/mV input module to the processor.
Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter 4–5 Decimal Bit 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 Octal Bit 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Bad Structure CJC over CJC Under 9 Overrange Bits 10 0 0 0 0 0 Underrange Bits Bad Cal Cal Cal Done Range 0 Diagnostic Status Pwr Up Thermocouple/mV Input Module (1794-IT8) Write Dec.
4–6 Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Word Write Word 0 Decimal Bit (Octal Bit) 00–01 (00–01) Description Module Data Type Bit Bit 02 (02) 03–05 (03–05) 01 00 Definition 0 0 oC (default) 0 1 oF 1 0 Bipolar counts scaled between –32768 and +32767 1 1 Unipolar counts scaled between 0 and 65535 Fixed Digital Filter – When this bit is set (1), a software digital filter is enabled.
Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Word Write Word 1 Decimal Bit (Octal Bit) 00–03 (00–03) Description Channel 0 Thermocouple Type Bit Write Word 2 03 02 01 00 Thermocouple Type – Range 0 0 0 0 Millivolts (default) 0 0 0 1 B 300 to 1800oC 0 0 1 0 E –230 to 1000oC (–382 to 1832oF) 0 0 1 1 J –195 to 1200oC (–319 to 2192oF) 0 1 0 0 K –230 to 1372oC (–382 to 2502oF) 0 1 0 1 R –50 to 1768oC (–58 to 3214oF) 0 1 1
4–8 Writing Configuration to and Reading Status from your Module with a Remote I/O Adapter Publication 1794-6.5.
Chapter 5 How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Chapter Objectives In this chapter, we tell you about: • • • • About DeviceNet Manager More Polled I/O Structure DeviceNetManager software I/O structure image table mapping factory defaults DeviceNetManager software is a software tool used to configure your Flex I/O DeviceNet adapter and its related modules. This software tool can be connected to the adapter via the DeviceNet network.
5–2 How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Adapter Input Status Word The input status word consists of: • I/O module fault bits – 1 status bit for each slot • node address changed – 1 bit • I/O status – 1 bit I/O Module Fault Bits Slot 0 Slot 1 1 0 Slot 2 Not Used Slot 3 9 8 7 6 5 4 3 2 Slot 5 Slot 4 10 through 15 Slot 6 15 Slot 7 Bit: I/O State Bit Node Address Changed Bit The adapter input status word bit descriptions are shown in the following
How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter System Throughput 5–3 System throughput, from analog input to backplane, is a function of: • the configured A/D filter first notch frequency • the number of channels actually configured for connection to a SEE PAGE 4–3 specific sensor The A/D converter which converts channel 0 through 7 analog data to a digital word provides a programmable first notch filter.
5–4 How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Dec.
How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Word Read Word 11 continu continued Write Word 1 Decimal Bit (Octal Bit) 03 (03) 04–06 (04–06) Description Powerup bit – this bit is set (1) until configuration data is received by the module. Critical Fault bits – If these bits are anything other than zero, return the module to the factory for repair.
5–6 How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Word Write Word 2 Decimal Bit (Octal Bit) 00–03 (00–03) Description Channel 0 Thermocouple Type Bit Write Word 3 03 02 01 00 Thermocouple Type – Range 0 0 0 0 Millivolts (default) 0 0 0 1 B 300 to 1800oC 0 0 1 0 E –230 to 1000oC (–382 to 1832oF) 0 0 1 1 J –195 to 1200oC (–319 to 2192oF) 0 1 0 0 K –230 to 1372oC (–382 to 2502oF) 0 1 0 1 R –50 to 1768oC (–58 to 3214oF) 0 1
How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Defaults 5–7 Each I/O module has default values associated with it. At default, each module will generate inputs/status and expect outputs/configuration.
5–8 How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter Publication 1794-6.5.
Chapter 6 Calibrating Your Module Chapter Objective In this chapter we tell you: • • • • General Information what tools are needed to calibrate how to calibrate out lead wire resistance calibrate your module manually calibrate your module using DeviceNetManager software Your module is shipped to you already calibrated. If a calibration check is required,follow the procedure below. Perform module calibration periodically, based on your application.
6–2 Calibrating Your Module Tools and Equipment In order to calibrate your thermocouple input module you will need the following tools and equipment: Tool or Equipment Description Analogic 3100, Data Precision 8200 or equivalent 0–100mV, 1µV resolution Precision Voltage Source or Thermocouple Simulator and Calibration source Thermocouple Simulator/Calibrator Model 1120 Industrial Terminal and Interconnect Cable Ectron Corporation 8159 Engineer Road San Diego, CA 92111-1980 Programming terminal fo
Calibrating Your Module 0 3 0 1 1 17 16 34 2 2 18 35 3 3 19 36 4 4 20 37 5 5 21 38 6 6 22 39 7 7 23 40 8 8 24 41 9 9 25 42 10 10 26 43 11 11 27 44 12 12 28 45 13 14 13 29 46 14 30 47 15 15 31 48 6–3 32 49 0 –15 A 16–33 B 33 50 51 34–51 C 1794-TB3, -TB3T a. Remove the decade box and voltage source. b. Reconnect the lead wires to the input terminals for this channel. Thermocouple or Sensor c. Repeat this procedure for the remaining channels.
6–4 Calibrating Your Module Flow Chart for Calibration Procedure Apply reference signal for offset calibration to each channel to be calibrated. Apply reference signal for gain calibration to each channel to be calibrated.
Calibrating Your Module 6–5 Calibration Setups Using a Precision Voltage Source 0 1 0 2 17 16 2 1 18 35 34 3 4 3 19 36 4 20 37 5 5 21 38 6 7 6 22 39 7 23 40 8 9 8 9 24 41 25 42 10 11 12 13 14 10 11 12 13 26 43 27 44 28 29 45 46 15 14 30 47 15 31 48 32 0 –15 A 16–33 B 33 49 50 51 34–51 C These terminals not on 1794-TB2 Precision Voltage Source 1794-TB2, -TB3 Note: Use 1794-TB2 and -TB3 terminal base units for millivolt inputs only.
6–6 Calibrating Your Module Read/Write Words for Calibration Dec. Bit 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 Octal Bit 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Read Word 10 0 0 0 0 0 Bad Cal Cal Done Cal Range 0 Diagnostic Status Pwr Up Bad Struct CJC over CJC Under Write Word 0 8-Bit Calibration Mask Cal Clk Cal hi Cal lo Filter Cutoff FDF Data Type Offset Calibration Inputs can be calibrated one at a time or all at once.
Calibrating Your Module 6–7 Gain Calibration After completing the offset calibration, proceed with the gain calibration. 1. Apply power to the module for 40 minutes before calibrating. 2. Connect 75.000mV across each input channel. Connect all high signal terminals together and attach to the positive lead from the precision voltage source. Connect all low signal terminals together and attach to the negative lead. 3.
6–8 Calibrating Your Module Calibrating Your Thermocouple/mV Module using DeviceNetManager Software (Cat. No. 1787-MGR) The following procedure assumes that you are using DeviceNetManager software (cat. no. 1787-MGR) and have the thermocouple/mV module installed in a working system. Offset Calibration Inputs can be calibrated one at a time or all at once. To calibrate the offsets for all inputs at once, proceed as follows: 1. Connect 0.000V across each input channel.
Calibrating Your Module 4. Click on 6–9 to get to the calibration screen. 5. Click on the channels you want to calibrate. 6. Click on the radio button . for offset calibration. Then click on 7. When calibration is complete, a notification will appear on the calibration status line. Publication 1794-6.5.
6–10 Calibrating Your Module Gain Calibration Make sure that you have calibrated the offset for this channel before calibrating the gain. 1. Connect 75.000mV across each input channel. Connect all high signal terminals together and attach to the positive lead from the precision voltage source. Connect all low signal terminals together and attach to the negative lead. 2. Click on the channels you want to calibrate. 3. Click on the radio button . for gain calibration. Then click on 4.
Calibrating Your Module The 6–11 button populates the screen with the actual values appearing at the inputs. Note that there is an implied decimal point to the left of the last 2 digits.. For example, channel 0 data value reads 7500. The actual reading is 75.00mV. After both offset and gain calibrations are successful, click on . You will be returned to the module configuration screen. Either save to the device (adapter), or save to a file by clicking on the appropriate button. Publication 1794-6.5.
6–12 Calibrating Your Module If you attempt to close without saving your configuration button, you will be information by clicking on the prompted to save the changes. Publication 1794-6.5.
Specifications1 – 1794-IT8 Thermocouple/mV Input Module Number of Inputs 8 Channels Module Location Cat. No. 1794-TB2, -TB3 and -TB3T Terminal Base Units2 Nominal Input Voltage Ranges +76.5mV Supported Thermocouple Types Type B: Type C: Type E: Type J: Type K: Type N: Type R: Type S: Type T: Type L: Resolution 16 bits (2.384 microvolts typical) Accuracy with fixed digital filter (at 24oC (+0.5oC)) 0.025% Full Scale Range +0.
A–2 Specifications Specifications1 – 1794-IT8 Thermocouple/mV Input Module Thermal Dissipation Maximum 10.2 BTU/hr @ 31.2V dc Keyswitch Position 3 General Specifications External dc Power Supply Voltage Voltage Range Supply Current 24V dc nominal 19.2 to 31.2V dc (includes 5% ac ripple) 19.2V dc for ambient temperatures less than 55oC 24V dc for ambient temperatures less than 55oC 31.2V dc for ambient temperatures less than 40oC See derating curve.
Specifications Derating Curve A–3 User Applied 24V dc Supply versus Ambient Temperature The area within the curve represents the safe operating range for the module under various conditions of user supplied 24V dc supply voltages and ambient temperatures. User Applied 24V dc Supply 31.2 24.0 19.2 40oC 50oC 55oC 25oC Ambient Temperature = Safe operating area Resolution Curves for Thermocouples Type B Thermocouple Resolution 1000Hz 500Hz 102.4 25.60 184.3 46.08 89.60 22.40 161.3 40.32 76.80 19.
A–4 Specifications Type E Thermocouple C F 1000Hz 500Hz 250Hz 10–100Hz 64.00 16.00 4.00 0.50 115.2 28.80 7.20 0.90 Resolution 51.20 92.16 12.80 23.04 3.20 5.76 0.40 0.72 38.40 69.12 9.60 17.28 2.40 4.32 0.30 0.54 25.60 46.08 12.80 11.52 1.60 2.88 0.20 0.36 12.80 23.04 6.40 5.76 0.80 1.44 0.10 0.18 0 –300 –508 –150 –238 150 302 0 32 300 572 450 842 Temperature 600 1112 750 1382 900 1652 1050 1922 1200 2192 C F Type C Thermocouple Resolution 1000Hz 500Hz 32.00 8.00 57.60 14.
Specifications A–5 Type J Thermocouple Resolution 1000Hz 500Hz 17.92 4.480 32.25 8.064 C F 250Hz 10–100Hz 0.140 1.120 0.252 2.016 15.36 27.65 3.840 6.912 0.960 1.728 0.120 0.216 12.80 23.04 3.200 5.760 0.800 1.440 0.100 0.180 10.24 18.43 2.560 4.608 0.640 1.152 0.080 0.144 7.680 13.82 1.920 3.456 0.480 0.864 0.060 0.108 5.120 9.216 1.280 2.304 0.320 0.576 0.040 0.072 2.560 4.608 0.640 1.152 0.160 0.288 0.020 0.
A–6 Specifications Type R Thermocouple C F 1000Hz 500Hz 250Hz 10–100Hz 102.4 25.60 6.40 0.80 184.3 46.08 11.52 1.44 Resolution 76.80 138.2 19.20 34.56 4.80 8.64 0.60 1.08 51.20 92.16 12.80 23.04 3.20 5.76 0.40 0.72 25.60 46.08 6.40 11.52 1.60 2.88 0.20 0.36 0 –300 –150 –508 –238 0 32 150 302 300 572 450 842 750 900 1050 1200 1350 1500 1650 1800 1382 1652 1922 2192 2462 2732 3002 3272 Temperature C F 600 1112 Type S Thermocouple Resolution 1000Hz 500Hz 76.80 19.20 138.2 34.
Specifications A–7 Type T Thermocouple Resolution 1000Hz 500Hz 102.4 25.60 184.3 46.08 89.60 22.40 161.3 40.32 76.80 19.20 138.2 34.56 64.00 16.00 115.2 28.80 51.20 12.80 92.16 23.04 38.40 9.60 69.12 17.28 25.60 6.40 46.08 11.52 12.80 3.20 23.04 5.76 C F 250Hz 10–100Hz 0.80 6.40 1.44 11.52 5.60 0.70 10.08 1.26 4.80 0.60 8.64 1.08 4.00 0.50 7.20 0.90 3.20 0.40 5.76 0.72 2.40 0.30 4.32 0.54 1.60 0.20 2.88 0.36 0.80 0.10 1.44 0.
A–8 Specifications Type L Thermocouple Resolution C F 1000Hz 500Hz 250Hz 10–100Hz 93.69 200.6 11.71 53.0 1.46 34.6 0.18 32.3 68.09 154.5 8.51 47.3 1.06 33.9 0.13 32.2 42.49 108.4 5.31 41.5 0.66 33.1 0.08 32.1 17.04 62.6 2.13 35.8 0.26 32.4 0.03 32.0 0 –200 –150 –328 –238 –100 0 50 100 200 –148 32 122 212 392 300 572 400 752 500 932 600 1112 700 1292 800 1472 Temperature C F Worst Case Accuracy for the Thermocouple/mV Module Publication 1794-6.5.
Specifications A–9 Error Due to Open Circuit Current Through Loop Resistance Input Type Error per Ohm of Loop Resistance B 0.091oC 0.164oF E 0.013oC 0.023oF J 0.016oC 0.029oF K 0.024oC 0.043oF R 0.076oC 0.137oF S 0.083oC 0.149oF T 0.022oC 0.040oF N 0.028oC 0.050oF C 0.055oC 0.099oF L 0.015oC 0.028oF mV 0.417µV (2.
A–10 Specifications Publication 1794-6.5.
Appendix B Thermocouple Restrictions (Extracted from NBS Monograph 125 (IPTS-68)) General Following are some restrictions extracted from NBS Monograph 125 (IPTS–68) issued March 1974 on thermocouples B, E, J, K, R, S and T: B (Platinum – 30% Rhodium vs Platinum – 6% Rhodium) Type Thermocouples “The ASTM manual STP 470 [1970] indicates the following restrictions on the use of B type thermocouples at high temperatures: They should not be used in reducing atmospheres, nor in those containing metallic or no
B–2 Thermocouple Restrictions E (Nickel–Chromium vs Copper–Nickel ) Type Thermocouple “Type E thermocouples are recommended by the ASTM Manual [1970] for use in the temperature range from –250 to 871C in oxidizing or inert atmospheres. The negative thermoelement is subject to deterioration above about 871C, but the thermocouple may be used up to 1000C for short periods.” “The ASTM Manual [1970] indicates the following restrictions .. at high temperatures.
Thermocouple Restrictions B–3 “Type J thermocouples are recommended by the ASTM [1970] for use in the temperature range from 0 to 760C in vacuum, oxidizing, reducing or inert atmospheres. If used for extended times above 500C, heavy gage wires are recommended because the oxidation rate is rapid at elevated temperatures.” “They should not be used in sulfurous atmospheres above 500C. Because of potential rusting and embrittlement, they are not recommended for subzero temperatures.
B–4 Thermocouple Restrictions K (Nickel–Chromium vs Nickel–Aluminum) Type Thermocouple “This type is more resistant to oxidation at elevated temperatures than the Types E, J or T thermocouples and consequently it finds wide application at temperatures above 500C.” “Type K thermocouples may be used at” liquid hydrogen “temperatures. However, their Seebeck coefficient (about 4uV/K at 20K) is only about one–half of that of Type E thermocouples.
Thermocouple Restrictions B–5 R (Platinum–13% Rhodium vs Platinum) and S (Platinum–10% Rhodium vs Platinum) Type Thermocouples “The ASTM manual STP 470 [1970] indicates the following restrictions on the use of S {and R} type thermocouples at high temperatures: They should not be used in reducing atmospheres, nor in those containing metallic vapor (such as lead or zinc), nonmetallic vapors (such as arsenic, phosphorous or sulfur) or easily reduced oxides, unless suitably protected with nonmetallic protecti
B–6 Thermocouple Restrictions “Type T thermocouples are recommended by the ASTM [1970] for use in the temperature range from –184 to 371C in vacuum or in oxidizing, reducing or inert atmospheres. The recommended upper temperature limit for continuous service of protected Type T thermocouples is set at 371C for AWG 14 (1.6mm) thermoelements, since Type TP thermoelements oxidize rapidly above this temperature.
Index Numbers 1794-TB3 example, thermocouple connection, 2–7 connecting wiring, 2–5, 6–6 considerations, pre–installation, 2–1 curent draw, through base units, 2–2 accuracy, worst case, A–7 curve derating, A–2 supply voltage vs.
I–2 Index K keyswitch positions, 2–4 M manual calibration, 6–4 mapping, 1794-IT8, 4–4, 5–3 module, shipping state, 6–1 module fault, 5–2 repeatability, worst case, A–8 resolution curves, A–3 type B thermocouple, A–3 type C thermocouple, A–4 type E thermocouple, A–3 type J thermocouple, A–4 type K thermocouple, A–5 type N thermocouple, A–7 type R thermocouple, A–5 type S thermocouple, A–6 type T thermocouple, A–6 module features, 1–3 module installation, 2–4 O offset calibration, 6–7 using DeviceNetMan
Allen-Bradley Publication Problem Report If you find a problem with our documentation, please complete and return this form. 8 Input Thermocouple/mV User Manual Pub. Name Cat. No. 1794-IT8 Check Problem(s) Type: Pub. No. 1794-6.5.7 Pub. Date April 1997 Part No.
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