Rockwell Automation 1794-IT8, 1794-IR8 User Manual

Installation Instructions

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FLEX I/O Thermocouple Input Analog
Module and RTD Module

Cat. No. 1794-IT8 and 1794-IR8

Important User Information

Because of the variety of uses for the products described in this publication, those
responsible for the application and use of these products 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. In no event will Rockwell Automation be responsible or liable for indirect or
consequential damage resulting from the use or application of these products.

Any illustrations, charts, sample programs, and layout examples shown in this publication
are intended solely for purposes of example. Since there are many variables and
requirements associated with any particular installation, Rockwell Automation does not
assume responsibility or liability (to include intellectual property liability) for actual use
based upon the examples shown in this publication.

Allen-Bradley publication SGI-1.1, Safety Guidelines for the Application, Installation and
Maintenance of Solid-State Control (available from your local Rockwell Automation office),
describes some important differences between solid-state equipment and
electromechanical devices that should be taken into consideration when applying products
such as those described in this publication.

Reproduction of the contents of this copyrighted publication, in whole or part, without
written permission of Rockwell Automation, is prohibited.

Throughout this publication, notes may be used to make you aware of safety
considerations. The following annotations and their accompanying statements help you to
identify a potential hazard, avoid a potential hazard, and recognize the consequences of a
potential 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 about practices or circumstances
that can lead to personal injury or death, property
damage, or economic loss.

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

When you insert or remove the module while
backplane power is on, an electrical arc can occur.
This could cause an explosion in hazardous location
installations. Be sure that power is removed or the
area is nonhazardous before proceeding.

FLEX I/O is grounded through the DIN rail to chassis
ground. Use zinc plated yellow-chromate steel DIN rail
to assure proper grounding. The use of other DIN rail
materials (e.g. aluminum, plastic, etc.) that can
corrode, oxidize, or are poor conductors, can result in
improper or intermittent grounding.

Preventing Electrostatic Discharge

This equipment is sensitive to electrostatic discharge,
which can cause internal damage and affect normal
operation. Follow these guidelines when you handle
this equipment:

• Touch a grounded object to discharge potential

static.

• Wear an approved grounding wriststrap.

• Do not touch connectors or pins on component

boards.

• Do not touch circuit components inside the

equipment.

• If available, use a static-safe workstation.

European Hazardous Location Approval

The following analog input modules are European Zone 2 approved: 1794-IR8
and 1794-IT8.

European Zone 2 Certification

This equipment is intended for use in potentially explosive
atmospheres as defined by European Union Directive 94/9/EC.

The LCIE (Laboratoire Central des Industries Electriques) certifies
that this equipment has been found to comply with the Essential
Health and Safety Requirements relating to the design and
construction of Category 3 equipment intended for use in
potentially explosive atmospheres, given in Annex II to this
Directive. The examination and test results are recorded in
confidential report No. 28 682 010.

Compliance with the Essential Health and Safety Requirements has
been assured by compliance with EN 50021.

Environment and Enclosure

This equipment is intended for use in a Pollution Degree 2
industrial environment, in overvoltage Category II applications
(as defined in IEC publication 60664-1), at altitudes up to 2000
meters without derating.

This equipment is considered Group 1, Class A industrial
equipment according to IEC/CISPR Publication 11. Without
appropriate precautions, there may be potential difficulties
ensuring electromagnetic compatibility in other environments
due to conducted as well as radiated disturbance.

This equipment is supplied as "open type" equipment. It must
be mounted within an enclosure that is suitably designed for
those specific environmental conditions that will be present and
appropriately designed to prevent personal injury resulting from
accessibility to live parts. The interior of the enclosure must be
accessible only by the use of a tool. Subsequent sections of this
publication may contain additional information regarding
specific enclosure type ratings that are required to comply with
certain product safety certifications.

See NEMA Standards publication 250 and IEC publication 60529,
as applicable, for explanations of the degrees of protection
provided by different types of enclosure. Also, see the
appropriate sections in this publication, as well as the
Allen-Bradley publication 1770-4.1 ("Industrial Automation
Wiring and Grounding Guidelines"), for additional installation
requirements pertaining to this equipment.

Observe the following additional Zone 2 certification
requirements.

• This equipment is not resistant to sunlight or

other sources of UV radiation.

• The secondary of a current transformer shall not

be open-circuited when applied in Class I, Zone
2 environments.

• Equipment of lesser Enclosure Type Rating

must be installed in an enclosure providing at
least IP54 protection when applied in Class I,
Zone 2 environments.

• This equipment shall be used within its

specified ratings defined by Allen-Bradley.

• Provision shall be made to prevent the rated

voltage from being exceeded by transient
disturbances of more than 40% when applied in
Class I, Zone 2 environments

Publication 1794-IN021D-EN-P - August 2003

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North American Hazardous Location Approval

The following analog input modules are Hazardous Location approved:
1794-IR8 and 1794-IT8.

The following information applies when
operating this equipme nt in hazardous locations:

Products marked “CL I, DIV 2, GP A, B, C, D” are suitable
for use in Class I Division 2 Groups A, B, C, D,
Hazardous Locations and nonhazardous locations only.
Each product is supplied with markings on the rating
nameplate indicating the hazardous location
temperature code. When combining products within a
system, the most adverse temperature code (lowest “T”
number) may be used to help determine the overall
temperature code of the system. Combinations of
equipment in your system are subject to investigation
by the local Authority Having Jurisdiction at the time of
installation.

EXPLOSION HAZARD

• Do not disconnect equipment
unless power has been
removed or the area is known
to be nonhazardous.

• Do not disconnect
connections to this equipment
unless power has been
removed or the area is known
to be nonhazardous. Secure any
external connections that mate
to this equipment by using
screws, sliding latches,
threaded connectors, or other
means provided with this
product.

• Substitution of components
may impair suitability for Class
I, Division 2.

• If this product contains
batteries, they must only be
changed in an area known to be
nonhazardous.

Informations sur l’utilisation de cet équipement en
environnements dangereux :

Les produits marqués "CL I, DIV 2, GP A, B, C, D" ne
conviennent qu’à une utilisation en environnements de
Classe I Division 2 Groupes A, B, C, D dangereux et non
dangereux. Chaque produit est livré avec des marquages
sur sa plaque d’identification qui indiquent le code de
température pour les environnements dangereux.
Lorsque plusieurs produits sont combinés dans un
système, le code de température le plus défavorable
(code de température le plus faible) peut être utilisé
pour déterminer le code de température global du
système. Les combinaisons d’équipements dans le
système sont sujettes à inspection par les autorités
locales qualifiées au moment de l’installation.

RISQUE D’EXPLOSION

• Couper le courant ou s’assurer
que l’environnement est classé
non dangereux avant de
débrancher l'équipement.

• Couper le courant ou s'assurer
que l’environnement est classé
non dangereux avant de
débrancher les connecteurs. Fixer
tous les connecteurs externes
reliés à cet équipement à l'aide de
vis, loquets coulissants,
connecteurs filetés ou autres
moyens fournis avec ce produit.

• La substitution de composants
peut rendre cet équipement
inadapté à une utilisation en
environnement de Classe I,
Division 2.

• S’assurer que l’environnement
est classé non dangereux avant
de changer les piles.

Installing Your Thermocouple or RTD Input Module

4. Position the module (4) with its alignment bar (5) aligned with the
groove (6) on the terminal base.

5. Press firmly and evenly to seat the module in the terminal base unit.
The module is seated when the latching mechanism (7) is locked into
the module.

Connecting Wiring for 1794-TB2, -TB3, -TB3S, -TB3T and -TB3TS Terminal Base Units

1. Connect individual high and low signal wiring to numbered terminals
on the 0-15 row (A) as indicated in the table. Use Belden 8761 cable
for mV signal wiring, or the appropriate thermocouple wire for your
thermocouples. (For more accurate readings in mV mode, use the
1794-TB3T or -TB3TS terminal base unit.)

The thermocouple/mV and RTD modules
do not receive power from the
backplane. +24V dc power must be
applied to the modules. If power is not
applied, the module position will appear
to the adapter as an empty slot in your
chassis.

You must power this module from the
same power supply that supplies the
adapter module, so they both power up
at the same time. You must cycle power
for the adapter to recognize this module.

2. Connect individual channel signal returns to the associated terminal
on row (B) as shown in the wiring table.

During mounting of all devices, be sure that all
debris (metal chips, wire strands, etc.) is kept from
falling into the module. Debris that falls into the
module could cause damage on power up.

The module mounts on a 1794 terminal base.

1. Rotate the keyswitch (1) on the terminal base (2) clockwise to position
3 as required for this type of module.

2. Make certain the flexbus connector (3) is pushed all the way to the left
to connect with the neighboring terminal base/adapter. You cannot
install the module unless the connector is fully extended.

3. Make sure the pins on the bottom of the module are straight so they
will align properly with the connector in the terminal base.

If you remove or insert the module while the
backplane power is on, an electrical arc can
occur. This could cause an explosion in
hazardous location installations. Be sure that
power is removed or the area is nonhazardous
before proceeding.

Publication 1794-IN021D-EN-P - August 2003

3. Connect individual channel shield returns to the associated terminal
on row (B) for 1794-TB3 or -TB3S or row (C) for the 1794-TB3T or

-TB3TS as shown in the wiring table..

Use the following Belden cables for connecting the
RTD to the terminal base unit.

RTD Type Length of Run/Humidity Level Belden Cable Number

2-wire Not applicable 9501
3-wire Less than 100ft (30.5m) with norma l humidity 9533

Over 100ft (30.5m) or high humidity

1 Greater than 55% for more than 8 hours.

4. Connect +24V dc power to terminal 34 on the 34-51 row (C).

5. Connect 24V dc common to terminal 16 on the 16-33 row (B).

To reduce susceptibility to noise, power
analog modules and digital modules from
separate power supplies. Do not exceed a
length of 9.8 ft (3m) for dc power cabling.

Do not daisy chain power or ground from this
terminal base unit to any ac or dc digital

module terminal base units.

6. 1794-IT8 only: On 1794-TB3T or -TB3TS terminal base units,

connect cold junction compensation (CJC) wiring to terminals 36, 37
and 38 for inputs 0-3, and terminals 47, 48 and 49 for inputs 4-7.
Connect the tail of the CJC to any of the associated thermocouple
input terminals: 0 thru 7 for CJC connected to terminals 36, 37 and
38; or 8 thru 15 for CJC connected to terminals 47, 48 and 49.

The tail of the CJC shares a terminal with an input.

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