Allen-Bradley 1785-LT/B — PLC-5 Small Processor Module | PLC-5 Platform
Engineering Background
The Allen-Bradley PLC-5 family, developed by Rockwell Automation, has been a cornerstone of industrial control architecture since the 1980s. Designed for demanding process and discrete manufacturing environments, the PLC-5 platform remains widely deployed in petrochemical, automotive, utilities, and heavy manufacturing facilities worldwide. The 1785-LT/B is the small-class processor within this family, offering a compact yet capable CPU solution for systems where rack space and cost efficiency are critical without sacrificing reliability or communication capability.
Product Positioning
The 1785-LT/B targets maintenance engineers and system integrators managing legacy PLC-5 installations who require a verified, drop-in replacement processor. It is equally suited for OEM machine builders maintaining installed base compatibility and for facilities executing phased modernization programs where full migration to ControlLogix is deferred. Konmask.com supplies this module with full traceability documentation, supporting procurement teams that operate under strict quality and compliance mandates.
Complete Technical Specifications
| Parameter | Specification |
|---|---|
| Catalog Number | 1785-LT/B |
| Platform | Allen-Bradley PLC-5 |
| Module Type | Small Processor (CPU) |
| Memory | 16K words user program memory |
| I/O Capacity | Up to 512 I/O points (local + remote) |
| Communication Ports | DH+ (Data Highway Plus), RS-232C |
| Scan Time | ~1 ms/K of logic (typical) |
| Power Supply Requirement | 1771-series backplane power |
| Rack Compatibility | 1771 I/O chassis (any slot) |
| Operating Temperature | 0 °C to +60 °C |
| Storage Temperature | -40 °C to +85 °C |
| Relative Humidity | 5% to 95% non-condensing |
| Certifications | UL, CSA, CE (per original OEM listing) |
| Weight | Approx. 1.4 kg |
| Firmware Series | Series B |
| Programming Software | RSLogix 5 / 6200 Series |
Proven Application Environments
- Petrochemical & Refining: Continuous process control loops, emergency shutdown sequencing, and DCS integration via DH+ networks.
- Automotive Manufacturing: Transfer line control, robotic cell coordination, and conveyor sequencing in legacy body-shop and powertrain facilities.
- Water & Wastewater Treatment: Pump station automation, SCADA gateway nodes, and remote I/O management across distributed plant layouts.
- Power Generation & Utilities: Turbine auxiliary control, switchgear sequencing, and substation automation where PLC-5 infrastructure remains in service.
- Food & Beverage: Batch processing, CIP (Clean-In-Place) sequencing, and packaging line control in facilities with validated legacy control systems.
- OEM Machine Builders: Spare parts inventory for installed machines under long-term service contracts requiring exact catalog-number replacement.
Engineering Advantages
- Drop-In Compatibility: Direct replacement for any 1785-LT/B in an existing 1771 chassis — no hardware modification or re-wiring required.
- DH+ Native Communication: Seamless integration with existing DH+ networks, PanelView HMIs, and SCADA systems without protocol converters.
- RSLogix 5 Support: Full compatibility with existing RSLogix 5 project files — upload, verify, and restore without program re-development.
- Proven MTBF: PLC-5 processors are documented for multi-decade service life in controlled industrial environments, reducing unplanned downtime risk.
- Compact Form Factor: Single-slot 1771 module footprint minimizes chassis space consumption in space-constrained control panels.
- Broad I/O Ecosystem: Compatible with the full 1771 I/O module library — analog, digital, thermocouple, RTD, and specialty modules.
System Architecture & Signal Flow
The 1785-LT/B installs into any slot of a 1771 I/O chassis and communicates with I/O modules via the 1771 backplane. The processor executes the user ladder logic program, scanning input image table data from local and remote I/O racks, executing logic, and updating the output image table each scan cycle.
Remote I/O communication is handled via the 1771-ASB adapter modules on remote racks, connected over the 1771 Remote I/O link. DH+ port enables peer-to-peer messaging with other PLC-5 or SLC-500 processors, as well as programming terminal access via RSLogix 5. The RS-232C port supports point-to-point ASCII device communication or DF1 protocol connections to SCADA hosts.
Typical Signal Flow: Field Devices → 1771 I/O Modules → 1771 Backplane → 1785-LT/B CPU (scan & execute logic) → Output Image Table → 1771 Output Modules → Actuators/Drives.
Sourcing & Quality Verification
- OEM-Traceable Stock: All 1785-LT/B units sourced through verified industrial surplus and authorized distribution channels with documented chain of custody.
- Pre-Shipment Inspection: Each module undergoes visual inspection for physical integrity, label authenticity, and connector condition prior to dispatch.
- Functional Test Available: Power-on functional verification available upon request — confirm with our technical team at time of order.
- Counterfeit Mitigation: Konmask applies multi-point authentication checks including date code verification, PCB marking inspection, and firmware series confirmation.
- Packaging: Shipped in anti-static ESD packaging with foam cushioning to IEC 61340-5-1 handling standards.
- Documentation: Certificate of conformance and inspection report available upon request for regulated industries.
Procurement Process
- Submit RFQ: Contact support@konmask.com with your required quantity, delivery timeline, and any functional test requirements.
- Quotation: Receive a formal quotation within 1 business day including unit price, lead time, and shipping options (DHL Express / FedEx International Priority).
- Order Confirmation: Issue PO against quotation. Payment terms: T/T (bank transfer), PayPal, or trade assurance as applicable.
- Quality Inspection: Pre-shipment inspection completed and inspection report issued if requested.
- Shipment & Tracking: Module dispatched with full tracking. Typical transit: 3–7 business days international, 1–3 days domestic (China).
- After-Sales Support: 90-day warranty on verified functional units. Technical support available via email and phone.
Technical FAQ
Q: Is the 1785-LT/B compatible with RSLogix 5 running on Windows 10/11?
A: RSLogix 5 is a 32-bit legacy application. It runs on Windows 10 (32-bit mode or compatibility layer) but is not officially supported by Rockwell on Windows 11. A dedicated programming workstation running Windows 7 or Windows XP is recommended for production environments.
Q: Can the 1785-LT/B communicate with ControlLogix or CompactLogix systems?
A: Direct backplane communication is not possible across platforms. However, DH+ to EtherNet/IP bridging via a 1756-DHRIO or 1784-PKTX card enables data exchange between PLC-5 and Logix-based systems.
Q: What is the maximum remote I/O distance supported?
A: The 1771 Remote I/O link supports distances up to 3,048 m (10,000 ft) at 57.6 Kbaud, or up to 304 m (1,000 ft) at 230.4 Kbaud, depending on cable type and network configuration.
Q: Do you offer exchange/repair services for faulty 1785-LT/B units?
A: Yes. Contact support@konmask.com with your unit’s fault description. We offer exchange programs and can coordinate third-party repair evaluation for units with repairable faults.
Q: How do I verify the firmware series of a unit before purchase?
A: The series designation (e.g., /B) is printed on the module label. We confirm this at inspection and include it in the shipment documentation. Specify your required series at time of RFQ if critical.
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Contact: support@konmask.com | +0086 19859288691
