Allen-Bradley 1785-LT3 PLC-5/12 Processor Module | PLC-5 Series Platform
Engineering Background
The Allen-Bradley PLC-5 series represents one of the most enduring and widely deployed programmable logic controller platforms in industrial automation history. Introduced by Rockwell Automation, the PLC-5 family has powered critical manufacturing, process control, and infrastructure applications across the globe for decades. The 1785-LT3 is a core processor module within this platform, designed to deliver reliable, deterministic control in demanding industrial environments.
Product Positioning
The 1785-LT3 PLC-5/12 Processor Module is engineered for facilities requiring a compact yet capable PLC-5 controller with a moderate I/O capacity. It is the preferred choice for system integrators and maintenance engineers who need a proven, drop-in replacement or expansion processor for existing PLC-5 chassis installations. Konmask supplies this module from verified surplus and refurbished inventory, fully tested and ready for deployment.
Complete Technical Specifications
| Parameter | Specification |
|---|---|
| Catalog Number | 1785-LT3 |
| Series / Platform | PLC-5/12 | PLC-5 Family |
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Maximum I/O Points | 512 discrete I/O |
| User Memory | 6K words (data + program) |
| Scan Time | ~1 ms/K of logic |
| Communication Ports | DH+ (Data Highway Plus) |
| Programming Software | RSLogix 5 / 6200 Series |
| Backplane Compatibility | 1771 I/O Chassis |
| Power Supply Requirement | Via 1771 chassis backplane |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
| Storage Temperature | -40°C to 85°C |
| Relative Humidity | 5% to 95% non-condensing |
| Product Weight | Approx. 1.4 kg |
| Form Factor | Single-slot 1771 chassis module |
| Status Indicators | RUN, FAULT, BATT, FORCE LEDs |
| Battery Backup | Lithium battery for memory retention |
Proven Application Environments
- Automotive Manufacturing: Body-in-white assembly lines, paint shop conveyors, and press control systems utilizing legacy PLC-5 infrastructure.
- Oil & Gas: Wellhead control panels, pipeline SCADA integration nodes, and compressor station automation.
- Water & Wastewater Treatment: Pump station sequencing, chemical dosing control, and filtration process management.
- Food & Beverage: Batch processing, filling line control, and CIP (Clean-In-Place) cycle management.
- Pulp & Paper: Winder control, digester sequencing, and stock preparation systems.
- Power Generation & Utilities: Substation automation, turbine auxiliary control, and load management panels.
- Material Handling: Conveyor routing, sortation systems, and automated storage/retrieval (AS/RS) interfaces.
Engineering Advantages
- Proven Platform Longevity: The PLC-5 architecture has a multi-decade installed base, ensuring long-term parts availability and deep community knowledge for maintenance teams.
- DH+ Network Integration: Native Data Highway Plus communication enables seamless integration with existing Allen-Bradley DH+ networks, HMIs (PanelView), and SCADA systems without additional gateways.
- Deterministic Scan Cycle: Consistent ~1 ms/K scan time ensures predictable, repeatable control logic execution critical for synchronized multi-axis or timed process applications.
- RSLogix 5 Compatibility: Full compatibility with RSLogix 5 programming software allows engineers to leverage existing ladder logic programs, reducing re-engineering costs.
- Battery-Backed Memory: Onboard lithium battery retains program and data memory during power loss, protecting against unplanned production downtime.
- Drop-In Replacement: Direct form-fit-function replacement for existing 1785-LT3 installations — no chassis modification or rewiring required.
System Architecture & Signal Flow
The 1785-LT3 processor module seats into a standard Allen-Bradley 1771 I/O chassis and communicates with discrete and analog I/O modules via the 1771 backplane. The processor executes the user ladder logic program cyclically, reading input image table data from I/O modules, processing control logic, and writing output image table commands back to output modules each scan cycle.
DH+ port connectivity allows the processor to participate in a multi-node Data Highway Plus network (up to 64 nodes), enabling peer-to-peer messaging, remote programming via RSLogix 5, and integration with Allen-Bradley PanelView HMI terminals and SCADA data collection systems. Program upload/download is performed over DH+ or via the 1784-KT/KTX interface card.
Sourcing & Quality Verification
- Source: Verified surplus and refurbished industrial inventory from decommissioned OEM and end-user facilities.
- Inspection: Each unit undergoes visual inspection for physical damage, connector integrity, and label verification prior to listing.
- Functional Testing: Available upon request — units can be bench-tested for power-on, communication, and basic I/O response prior to shipment.
- Authenticity: All modules are sourced from traceable industrial channels. Konmask does not deal in counterfeit or unauthorized reproductions.
- Packaging: Anti-static bagged and foam-cushioned for safe international transit.
Procurement Process
- Inquiry: Submit your requirement via the product page or contact support@konmask.com with your target quantity and delivery timeline.
- Quote: Konmask will respond within 1 business day with pricing, lead time, and stock confirmation.
- Order Confirmation: Purchase order or online checkout accepted. Proforma invoice available for wire transfer payments.
- Quality Check & Dispatch: Unit inspected, packaged, and dispatched with tracking information provided.
- After-Sales Support: Technical assistance available post-delivery for installation and commissioning queries.
Technical FAQ
Q: Is the 1785-LT3 compatible with ControlLogix or CompactLogix chassis?
A: No. The 1785-LT3 is exclusively compatible with the Allen-Bradley 1771 I/O chassis. It is not interchangeable with ControlLogix (1756) or CompactLogix (1769) platforms.
Q: What programming software is required?
A: RSLogix 5 (current Rockwell offering) or legacy 6200 Series software. RSLogix 5 requires a valid Rockwell Automation software license.
Q: Can the DH+ port communicate with Ethernet/IP networks?
A: Not natively. A protocol gateway such as the ProSoft MVI56-DFNT or similar DH+-to-Ethernet/IP bridge is required for integration with modern Ethernet-based systems.
Q: What is the battery replacement part number?
A: The onboard memory backup battery is typically a 1770-XY or equivalent lithium cell. Consult the 1785-LT3 installation manual (Pub. 1785-6.5.12) for the exact replacement specification.
Q: Do you offer a warranty?
A: Konmask offers a 90-day functional warranty on all tested surplus modules. Terms are confirmed at time of order.
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