Description:
The 1785‑CHBM is a Hot Backup Memory Cartridge for Allen‑Bradley’s PLC‑5 ControlNet series processors. It provides 100K words of battery‑backed SRAM and enables a redundant (hot backup) system when used in pairs with compatible PLC‑5 controllers (e.g., 1785‑L40C15, L80C15). This module ensures program and data synchronization between primary and secondary CPUs, allowing for fault‑tolerant operation in critical industrial processes.
Application Scenarios:
In a chemical plant’s batch reactor control system, two PLC‑5/40C processors are equipped with 1785‑CHBM modules. The primary controller handles the active process, while the secondary runs in standby with synchronized data. If the primary CPU fails or is taken offline for maintenance, the 1785‑CHBM system triggers an automatic switchover (typically within 50 ms). This seamless transition prevents a reactor shutdown, avoiding costly production losses and ensuring continuous monitoring of critical safety interlocks.
Parameter:
| Main Parameters | Value / Description |
|---|---|
| Product Model | 1785‑CHBM |
| Manufacturer | Allen‑Bradley (Rockwell Automation) |
| Product Type | Hot Backup Memory Cartridge / Redundancy Module |
| Compatible Processors | PLC‑5 ControlNet Series (1785‑L20C15, L40C15, L80C15, L46C15) |
| Memory Capacity | 100K words (Battery‑Backed Static RAM) |
| Memory Protection | Write‑protect via physical jumper on module |
| Battery Type | Integrated Lithium (Lithium Thionyl Chloride, non‑rechargeable) |
| Battery Life | ~5 years @ 25°C (typical, varies with temperature) |
| Backup Function | Enables processor‑to‑processor hot backup (requires two modules) |
| Sync Interface | DB‑9 style connector for inter‑module sync cable |
| Sync Cable Length | Typically ≤ 15 meters (shielded twisted pair) |
| Power Source | Powered via PLC‑5 processor’s memory expansion port |
| Status Indicators | LEDs for Power, Battery Status, Fault, Sync Status |
| Operating Temperature | 0 °C to 60 °C (32 °F to 140 °F) |
| Certifications | UL, cULus, CE, C‑Tick, CSA (Industrial Controls) |
| Weight | Approx. 70–80 grams |
Technical Principles and Innovative Values:
- Innovation Point 1: Deterministic ControlNet Redundancy. The 1785‑CHBM extends the PLC‑5’s architecture to support ControlNet‑based hot backup. It maintains a mirrored image of the primary processor’s program and data tables in the secondary unit. This allows a standby PLC‑5 to take over scanning and controlling remote I/O (via ControlNet) within milliseconds if the primary fails, ensuring no single point of failure in the controller layer for high‑availability systems.
- Innovation Point 2: Integrated Battery‑Backed SRAM Architecture. Unlike EEPROM modules used for program storage, the 1785‑CHBM utilizes 100K words of Static RAM with an integrated lithium battery. This provides fast, unlimited write cycles for real‑time data synchronization between the redundant pair. The battery ensures data retention during power outages, and the physical write‑protect jumper prevents accidental corruption during maintenance.
- Innovation Point 3: Synchronized State Machine. The module implements a synchronization protocol over a dedicated serial link (sync cable). It continuously compares the state of the primary and secondary processors, ensuring that timers, counters, and process data are identical. If a divergence is detected (e.g., due to a memory fault), the system can flag a fault and initiate a controlled switchover, maintaining process integrity.
