Allen-Bradley 1785-LT3
Allen-Bradley 1785-LT3
Allen-Bradley 1785-LT3
Allen-Bradley 1785-LT3
Allen-Bradley 1785-LT3
Allen-Bradley 1785-LT3
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1785-LT3

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The Allen-Bradley 1785-LT3 Processor Module is specifically designed to handle complex industrial automation control tasks and distributed I/O communication requirements.
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Technical specifications for 1785-LT3

  • Manufacturer:
    Allen-Bradley
  • Part Number:
    1785-LT3
  • Product Family:
    PLC-5
  • Product Type:
    Processor Module
  • Max Total I/O:
    512
  • Analog I/O:
    256
  • DH+ Channel:
    Yes
  • Remote I/O Channel:
    Yes
  • Number of Words:
    6 Kilowords SRAM
  • Backplane Requirement:
    2.5 Amperes at 5 Volts DC
  • Max Analog I/O:
    3072
  • Weight:
    1.44 kg
  • Estimated shipping dimensions:
    4.6x16x27.4cm
  • Tariff Code:
    8537101190
  • Country of origin:
    USA
  • Place of shipment:
    Xiamen,Fujian,China
By purchasing this item, you agree to the Terms & Conditions, ApterPower is not an authorized distributor for listed manufacturers or tradenames and therefore the manufacturer's warranty does not apply. All our products come with ApterPower's 1-year warranty.

More Information

Overview Manuals Specifications Use Cases Certifications & Standards Firmware & Updates

Features:

  • Bridge Between AC Power Input and PLC-5 Rack Backplane
  • Integrates AC/DC Power Conversion with DH+ Network Communication
  • Functions in Coordination with PLC-5 Family Processors and I/O Modules
The Allen-Bradley 1785-LT3 Processor Module operates as the central processing unit in a PLC-5 rack, providing reliable control logic execution and communication management for all modules within the system. It continuously processes I/O data from 512 points and distributes control commands through the rack backplane to support steady state operation of all connected monitors and modules. Seamless communication is standard with the 1785-LT3, and using the DH+ Channel enables seamless data exchange with higher-level computers and other processors in the event of complex network requirements. The 1785-LT3 has made improvements in several areas over previous processor designs in addition to incorporating remote I/O adapter capability within the PLC-5 rack.

The 1785-LT3 provides essential processing functions common to the entire rack, and is a critical component of the control path, directly affecting the proper, normal operation of the overall automation system. One 1785-LT3 processor module is required per rack depending on the desired control complexity. The 1785-LT3 occupies a dedicated slot in the rack and is always positioned to manage the primary control functions.

For Remote I/O applications, the 1785-LT3 Processor Module requires connection to the Remote I/O Channel (Adapter Only) to interface with distributed field devices. In addition to standard local I/O operation, the remote configuration also performs automatic scanning. The 1785-LT3 remote I/O configuration executes communication using the 57.6 kbps transmission rate specified in the module specifications. Using this method, the remote I/O system continually monitors the status of all connected stations. If the system detects that a remote station is no longer providing valid data (outside configured response/tolerance levels), it will automatically flag the condition and place an event in the system diagnostic list.

The 1785-LT3 Allen-Bradley Processor Module may still be available for purchase and support from Apter Power beyond End-Of-Life (EOL) by the manufacturer (OEM).
Allen-Bradley 1785-LT3 Processor Module Manuals,Datasheets,Link Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.
Allen-Bradley 1785-LT3 Processor Module Specs

General

  • Manufacturer Allen-Bradley
  • Model 1785-LT3
  • Condition New Original ready stock
  • Product Family 1785-LT,1785-LT2,1785-LT4
Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.
  • Legacy System Maintenance: Replaces faulty modules to minimize downtime in factories running vintage Rockwell Automation PLC-5 control systems.
  • Machine Automation: Controls synchronized assembly lines, pneumatic sequencing, and packaging hardware with an average execution speed of 8 ms per 1,000 words.
  • Remote I/O Network Expansion: Interfaces with up to 4 I/O racks and 32 universal remote chassis over a 57.6 kbps transmission line.
  • Memory Optimization: Executes repetitive logic structures and plant subroutines via Jump-to-Subroutine (JSR) commands to maximize the 6K internal memory capacity.
  • Peer-to-Peer Communication: Connects multiple classic processors over a Data Highway Plus (DH+) daisy chain to share plant metrics or link central programming terminals.
  • CSA Certification: Approved by the Canadian Standards Association for operational safety in industrial control deployments.
  • Class I, Division 2: Rated for deployment in hazardous environments categorized across Groups A, B, C, and D explosive atmospheres.
  • EN 61131-2 Standard: Meets European compliance criteria for programmable controller safety, environmental resistance, and electrical parameters.
  • EMC Directive Compliance: Conforms to industrial electromagnetic compatibility limits for emissions and electrostatic/RF immunity.
  • Physical PROM Upgrades: Classic Series A hardware stores operational software on chipsets. Physical updates require replacing the internal socketed communication plug PROMs (such as chip U7 or U31) rather than using modern desktop software utilities.
  • Software Verification: Open the system configuration inside RSLogix 5 software, go online, and open Controller Properties to check the active firmware revision without opening the chassis.
  • Legacy Tool Requirements: System-based updates require the vintage 1785 PLC-5 Programmable Controller Flash Tool suite instead of standard modern ControlFlash software.
Description
The Allen-Bradley 1785-LT3 is a processor module equipped with 6K words of memory and a backplane current rating of 2.5 A at 5V DC. This module includes a Control Coprocessor Expansion Port and features comprehensive hardware selection, layout, and addressing capabilities to optimize system configuration. It utilizes an advanced control strategy alongside special programming features like Sequential Function Charts (SFC). These features allow engineers to fully develop, enter, and test programs before deployment. This product is specifically designed to handle mid-sized industrial control tasks requiring synchronized step-by-step logic, solving the problem of complex code organization by streamlining sequential programming execution. The functional specifications of the 1785-LT3 are advanced enough to serve as a reliable platform for a document sign-off program based on rigorous analysis and test procedures.

For network integration, the Allen-Bradley 1785-LT3 processor module features a dedicated Data Highway Plus (DH+) channel and a Remote I/O channel configured for adapter mode only. The module operates at a remote I/O transmission rate of 57.6 kbps to ensure reliable communication with distributed devices. Through its DH+ link, the 1785-LT3 supports remote programming, direct information access, and data transfers to higher-level supervisory computers. It functions efficiently as a PLC-5 programming processor, communicating seamlessly with programming terminals and other processors while supporting up to 64 stations on a single DH+ network link. This product is specifically designed to handle factory-wide data isolation and remote configuration challenges, solving the problem of high maintenance downtime by allowing technicians to modify and diagnose the processor from a single centralized engineering station.

Environmental durability is a key characteristic of the Allen-Bradley 1785-LT3 processor module, which manages up to 512 local and remote input/output points. The 1785-LT3 is built to operate reliably within a temperature range of 0 to 60 °C (32 to 140 °F). For storage and transport, it sustains a non-operating temperature range of -40 to 85 °C (-40 to 185 °F). Keeping the 1785-LT3 module in environments that exceed or fall below these specified thermal limits will cause permanent hardware damage. This product is specifically designed to handle automation tasks in standard manufacturing plant floors, solving the problem of component degradation under varying thermal conditions while managing a fixed density of 512 I/O signals safely.
Revisions

Revision Part #

Also known as

1785-LT3 Ser A
1785-LT3/A, Series A, Rev A
Alternative Names
1785LT3 17B5-LT3 17B5LT3 I785-LT3 I785LT3 I7B5-LT3 1785-LT 1785-LT2 1785-LT4
Technical notes
The 1785-LT3 features 512 I/O points, making it well-suited for medium-scale control applications where comprehensive input and output management is essential for production line coordination and equipment monitoring.
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FAQS

The following is a list of questions commonly asked by our customers. Please contact us if you have a question about our process that is not answered below.
What is the main purpose of the 1785-LT3?
The 1785-LT3 is used to manage industrial automation tasks that require reliable logic processing, distributed I/O communication, and network connectivity between controllers and field devices.
Does the 1785-LT3 support advanced programming features?
Yes. The module supports sequential function chart (SFC) programming along with special PLC-5 programming features. These tools help engineers create, test, and validate automation logic.
Why is the 1785-LT3 important?
The 1785-LT3 combines processor control, DH+ communication, and distributed I/O management in one module. It provides reliable automation control for manufacturing systems that require networked device coordination.