Allen-Bradley 1785-BCM Back-up Communications Module | Replacement, Equivalent & Selection Guide
The Allen-Bradley 1785-BCM is a Back-up Communications Module designed for use in PLC-5 redundant control systems. It enables seamless switchover between primary and secondary processors, ensuring continuous operation in mission-critical industrial environments. This guide covers technical specifications, compatible replacements, application scenarios, and sourcing information to help engineers and procurement teams make informed decisions.
Technical Specifications
- Part Number: 1785-BCM
- Manufacturer: Allen-Bradley (Rockwell Automation)
- Series: PLC-5
- Function: Back-up Communications Module for redundant PLC-5 systems
- Communication: Supports Data Highway Plus (DH+) and Remote I/O (RIO)
- Redundancy Type: Hot-standby / Bumpless transfer
- Backplane Compatibility: PLC-5 chassis (1771 series)
- Weight: 560 g
- Operating Temperature: 0°C to 60°C
- Humidity: 5% to 95% non-condensing
- Certifications: UL, CE
Compatible Replacement & Equivalent Models
When the 1785-BCM is unavailable or end-of-life, the following models may serve as functional equivalents or replacements depending on system configuration:
- 1785-BCMK – Enhanced version of the BCM with additional diagnostics; direct drop-in for most PLC-5 redundant systems
- 1785-L80B / 1785-L80E – PLC-5 processors with integrated redundancy support; consider when upgrading the full redundancy pair
- 1756-RM2 (ControlLogix) – Redundancy Module for ControlLogix platform; recommended for system migration from PLC-5 to ControlLogix
- 1756-RM2XT – Extended-temperature variant of the ControlLogix Redundancy Module for harsh environments
- Third-party equivalents: Consult Konmask technical team for vetted third-party BCM-compatible modules
Note: Always verify firmware revision compatibility and chassis slot requirements before substituting modules.
Why Choose the Original Model
- Proven Reliability: The 1785-BCM has decades of field-proven performance in process and manufacturing industries
- Bumpless Switchover: Ensures zero-disruption transfer between primary and backup processors
- Native DH+ & RIO Support: Eliminates the need for additional communication bridges in legacy PLC-5 architectures
- Rockwell Ecosystem Integration: Fully supported by RSLogix 5 and FactoryTalk diagnostics
- Regulatory Compliance: UL and CE certified for use in regulated industries including oil & gas, water treatment, and pharmaceuticals
Typical Applications
- Redundant PLC-5 control systems in continuous process plants
- Oil & gas pipeline SCADA and safety instrumented systems (SIS)
- Water and wastewater treatment automation
- Pharmaceutical batch control with high-availability requirements
- Power generation and utility distribution control
- Automotive and discrete manufacturing lines requiring zero-downtime operation
System Compatibility
- PLC Platform: Allen-Bradley PLC-5 series (1785-Lxx processors)
- Chassis: 1771-A1B, 1771-A2B, 1771-A3B, 1771-A4B series
- Programming Software: RSLogix 5 (v7.x and above recommended)
- Communication Networks: Data Highway Plus (DH+), Remote I/O (RIO)
- Redundancy Pair: Must be used with a compatible 1785-Lxx primary/secondary processor pair
- Not Compatible With: ControlLogix (1756), CompactLogix (1769), or MicroLogix platforms without migration
Selection Guide
Use the following criteria to determine the right module for your application:
- Existing PLC-5 system, BCM replacement only → 1785-BCM or 1785-BCMK (preferred)
- Existing PLC-5 system, processor upgrade needed → 1785-L80B or 1785-L80E with new BCM pair
- Migrating to ControlLogix platform → 1756-RM2 + ControlLogix processor pair; requires RSLogix 5000 and new I/O wiring
- Harsh environment (extended temp) → 1756-RM2XT for ControlLogix migration
- Budget-constrained, legacy maintenance → Contact Konmask for refurbished 1785-BCM with warranty
Quality Assurance & Sourcing
- All 1785-BCM modules sourced by Konmask undergo multi-point inspection including visual, functional, and communication verification
- Modules are tested against Rockwell Automation factory specifications prior to shipment
- Traceability documentation available upon request (batch records, test reports)
- Refurbished units include 12-month warranty; new/surplus units include manufacturer warranty where applicable
- Anti-counterfeit verification: serial number cross-check with Rockwell Automation database
How to Order
- Step 1: Confirm your PLC-5 processor model and firmware revision
- Step 2: Verify chassis slot availability and backplane compatibility
- Step 3: Contact Konmask via email or phone with your part number and quantity
- Step 4: Receive quotation with lead time, warranty terms, and shipping options
- Step 5: Place order — standard lead time 3–7 business days; expedited available
📧 Email: support@konmask.com
📞 Phone/WhatsApp: +0086 19859288691
🌐 Website: https://Konmask.com
Replacement & Compatibility FAQ
Q: Can the 1785-BCM be used with any PLC-5 processor?
A: No. It is specifically designed for PLC-5 redundant systems. The primary and secondary processors must be compatible 1785-Lxx models configured for redundancy.
Q: Is the 1785-BCMK a direct replacement for the 1785-BCM?
A: In most cases, yes. The BCMK offers enhanced diagnostics but is backward compatible. Verify firmware revision requirements before substituting.
Q: Can I migrate from PLC-5 redundancy to ControlLogix without replacing all I/O?
A: Partial migration is possible using 1756-DHRIO or 1756-RIO bridge modules to retain existing Remote I/O. Full migration is recommended for long-term supportability.
Q: Does Konmask provide installation support?
A: Yes. Our technical team can provide configuration guidance, wiring diagrams, and remote commissioning support for qualified projects.
Q: What is the lead time for a 1785-BCM?
A: Typically 3–7 business days for in-stock units. Contact us for real-time availability.
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Contact: support@konmask.com | +0086 19859288691
