Redundant Network Solution – Allen-Bradley 1785-BEM | PLC-5 Series
Where This Product Is Used
The Allen-Bradley 1785-BEM Backup Communications Expansion Module is deployed in mission-critical industrial environments where network redundancy and uninterrupted PLC-5 communication are non-negotiable. Typical application sites include:
- Oil & Gas Processing Plants — Backup communication paths for SCADA-linked PLC-5 controllers managing pipeline pressure, valve sequencing, and emergency shutdown (ESD) systems.
- Automotive Assembly Lines — Redundant data highways ensuring zero-downtime communication between PLC-5 racks and HMI/SCADA stations on high-throughput production lines.
- Water & Wastewater Treatment Facilities — Failover communication for remote pump stations and chemical dosing systems where loss of control signal triggers regulatory non-compliance.
- Power Generation & Utilities — Backup channel for DCS-integrated PLC-5 nodes controlling turbine auxiliaries, switchgear, and load-shedding logic.
- Pharmaceutical & Food Manufacturing — Validated control networks requiring continuous audit-trail communication between batch controllers and MES systems.
- Mining & Minerals Processing — Harsh-environment installations where primary network cables are vulnerable to physical damage, requiring automatic failover to the BEM channel.
Technical Specifications
| Parameter | Specification |
|---|---|
| Part Number | 1785-BEM |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Series | PLC-5 |
| Module Type | Backup Communications Expansion Module |
| Function | Provides redundant communication path for PLC-5 processors via Data Highway Plus (DH+) |
| Compatible Processors | PLC-5/20, PLC-5/30, PLC-5/40, PLC-5/60, PLC-5/80 (Enhanced series) |
| Communication Protocol | Data Highway Plus (DH+) |
| Backplane Interface | PLC-5 I/O chassis expansion slot |
| Weight | 500 g (approx.) |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
| Storage Temperature | -40°C to 85°C (-40°F to 185°F) |
| Relative Humidity | 5% to 95% non-condensing |
| Certifications | UL Listed, CE Marked, CSA Certified |
Why Engineers Specify This Model
- Automatic Failover: The 1785-BEM seamlessly switches to the backup DH+ communication path upon detection of primary channel failure — no manual intervention required, no process interruption.
- Native PLC-5 Integration: Designed as a drop-in expansion module for existing PLC-5 chassis; no firmware changes or processor replacement needed.
- Proven DH+ Architecture: Data Highway Plus remains the backbone of thousands of legacy Allen-Bradley installations. The BEM extends the operational life of these systems without costly migration to ControlLogix.
- Deterministic Communication: DH+ token-passing protocol guarantees bounded message delivery times — critical for time-sensitive control loops and ESD applications.
- Reduced MTTR: With a backup channel already active, mean time to repair drops dramatically. Maintenance teams can address primary network faults without halting production.
- Cost-Effective Redundancy: Compared to full processor redundancy (1785-CHBM), the BEM provides communication-layer redundancy at a fraction of the cost — ideal for sites where processor failure risk is low but network reliability is paramount.
Complete System Bill of Materials
For a fully redundant PLC-5 communication node using the 1785-BEM, engineers typically specify the following components:
| Item | Part Number | Description |
|---|---|---|
| 1 | 1785-BEM | Backup Communications Expansion Module (this item) |
| 2 | 1785-L40E / L60E / L80E | PLC-5 Enhanced Processor (DH+ capable) |
| 3 | 1771-A4B / A3B1 | PLC-5 I/O Chassis (4-slot or 8-slot) |
| 4 | 1770-CD | DH+ Trunkline Cable (Belden 9463 equivalent) |
| 5 | 1770-XT | DH+ Network Terminator (one per network end) |
| 6 | 1785-ME16 | EEPROM Memory Module (for program backup) |
| 7 | 1771-P4S1 | Power Supply for I/O Chassis |
| 8 | 1784-PCMK / PKTX | DH+ Interface Card for programming terminal |
Contact Konmask.com for bundle pricing on complete BOM packages.
Compliance & Industry Standards
- UL 508 — Industrial Control Equipment (UL Listed)
- CSA C22.2 No. 142 — Process Control Equipment (CSA Certified)
- CE Marking — Compliant with EU Low Voltage Directive (LVD) and EMC Directive
- IEC 61131-2 — Programmable Controllers: Equipment Requirements and Tests
- NEMA ICS 2 — Industrial Control Devices, Controllers, and Assemblies
- RoHS Compliant — Restriction of Hazardous Substances (where applicable to original manufacture date)
Note: Compliance certifications apply to original Allen-Bradley manufacture. Konmask.com supplies genuine OEM parts; no modifications are made to hardware or firmware.
Quality Assurance & Sourcing
Konmask.com specializes in the supply of genuine, tested Allen-Bradley / Rockwell Automation components for industrial automation applications. Our quality process for the 1785-BEM includes:
- Visual Inspection: All modules inspected for physical damage, corrosion, bent pins, and label integrity prior to listing.
- Functional Verification: Where test equipment is available, modules are bench-tested for backplane communication and DH+ channel response.
- Traceability: Serial numbers and date codes are recorded. Modules sourced from decommissioned OEM installations or authorized surplus channels — never counterfeit or cloned.
- Packaging: Anti-static bagging, foam cushioning, and double-wall carton for international shipment.
- Warranty: 90-day replacement warranty against DOA (Dead on Arrival) or latent defects discovered during installation.
How to Source This Part
- Add to Cart — Click the purchase button above to place an order directly through Konmask.com.
- Request a Quote — For bulk orders (3+ units), OEM project requirements, or BOM-level procurement, email support@konmask.com with your project details.
- Urgent Requirement — Call or WhatsApp +0086 19859288691 for same-day stock confirmation and expedited shipping options.
- Lead Time — In-stock units ship within 1–2 business days. Out-of-stock items are sourced within 5–15 business days depending on global availability.
- Export & Customs — Konmask.com handles export documentation, commercial invoices, and HS code classification for international buyers.
Application-Specific FAQ
Q: Is the 1785-BEM compatible with all PLC-5 processors?
A: The 1785-BEM is compatible with PLC-5 Enhanced processors (1785-L20E, L40E, L60E, L80E). It is not compatible with standard (non-Enhanced) PLC-5 processors or PLC-5/250 series. Verify your processor catalog number before ordering.
Q: Can the 1785-BEM be used to connect two separate DH+ networks?
A: No. The BEM provides a backup communication path on the same DH+ network segment. For bridging between two DH+ networks, specify the 1785-KA5 or use a 1756-DHRIO gateway module.
Q: Does installing the 1785-BEM require a processor firmware upgrade?
A: In most cases, no. However, Rockwell Automation recommends verifying that your PLC-5 Enhanced processor firmware is at Series D or later for full BEM feature support. Contact Konmask.com if you need firmware version guidance.
Q: What happens if both the primary and backup communication channels fail?
A: The PLC-5 processor will continue executing its ladder logic program in its last known state (per the processor’s fault routine configuration). Communication loss does not inherently cause a processor fault unless programmed to do so via the communication status bits.
Q: Can I use the 1785-BEM in a ControlLogix or CompactLogix system?
A: No. The 1785-BEM is exclusively designed for the PLC-5 chassis architecture. For ControlLogix redundant communication, specify the 1756-RM2 redundancy module or 1756-DHRIO for DH+ connectivity.
Q: Do you supply the 1785-BEM with a warranty?
A: Yes. Konmask.com provides a 90-day replacement warranty. For extended warranty or service contracts, contact our sales team.
© 2026 Konmask.com. All rights reserved.
Original Source: https://Konmask.com
Contact: support@konmask.com | +0086 19859288691
