1797-CEC | Allen-Bradley | FLEX Ex FlexBus Connector Module

Module Overview

The 1797-CEC is a specialized backplane extension and bus connector module within the Allen-Bradley FLEX Ex I/O family. Its primary function is to provide an intrinsically safe (IS) compatible mechanism to connect the internal communication bus (FlexBus) across different sections of a DIN rail. This module is essential for "intermixed" systems where a designer needs to combine standard FLEX I/O modules and intrinsically safe FLEX Ex modules on the same adapter group. It effectively acts as a bridge that maintains the integrity of the IS backplane while allowing the system to scale up to its maximum capacity of eight I/O modules.

Detailed Engineering Specifications

The 1797-CEC is a passive mechanical and electrical interface designed for hazardous area backplane continuity.

• Product Type: FlexBus Connector / Bus Isolator Extension

• Product Line: FLEX Ex 1797

• I/O Module Capacity: Supports up to 8 I/O modules on the "slave" side

• Function: Connects standard FLEX I/O adapters/modules to FLEX Ex modules

• Mounting: 35mm x 7.5mm DIN Rail (Zinc-plated yellow-chromate steel recommended)

• Protection Factor: IP20 (Open-style equipment)

• Operational Temperature: -20°C to 70°C (-4°F to 158°F)

• Storage Temperature: -40°C to 85°C (-40°F to 185°F)

• Relative Humidity: 5% to 95% (Non-condensing)

• Operating Shock: 30g peak acceleration

• Physical Weight: 1.17 lbs (0.53 kg)

• Hazardous Location Rating: II 3G Ex nA IIC (ATEX compliant for Zone 2)

System Architecture and Intermixing

The 1797-CEC is typically used in conjunction with the 1797-BIC (Bus Isolator Module). In an intermixed system, standard FLEX I/O modules are mounted to the left of the 1797-CEC, while the intrinsically safe FLEX Ex modules are mounted to the right. This physical separation is critical for:

• Power Conversion: Helping convert hazardous power to IS-safe power for the bus receiver circuitry.

• Signal Isolation: Ensuring that non-IS signals cannot propagate into the IS-protected portion of the backplane.

• Grounding: Maintaining a consistent ground path across the DIN rail through the use of high-conductivity rail materials.

Installation Guidelines

To install the 1797-CEC, follow these critical steps to ensure backplane alignment:

1. Remove Cover Plugs: Clear any protective plugs from the male FlexBus connector of the adjacent module.

2. DIN Rail Alignment: Hook the top of the module onto the DIN rail and rotate it downward until the locking tab snaps into place.

3. Horizontal Connection: Firmly push the module to the left into the adjacent adapter or terminal base until the units interconnect.

4. Locking: Use DIN rail locks (like the 1492-EA35) to prevent accidental separation, especially in high-vibration environments.

Technical FAQ

Can I place the 1797-CEC between two standard FLEX I/O modules?

No. The 1797-CEC must be positioned to the right of standard FLEX I/O modules. It serves as the transition point into the FLEX Ex (intrinsically safe) portion of the rack.

Does this module require its own power supply?

The 1797-CEC itself is a connector and isolator interface; however, the FLEX Ex modules connected to its "slave" side must be powered by a 1797-PS series intrinsically safe power supply to maintain the IS rating of the system.

Is this module still being manufactured?

The 1797-CEC has been discontinued by Rockwell Automation. It is primarily available through specialized industrial surplus and repair vendors. When sourcing a replacement, ensure the unit carries the appropriate ATEX or UL/FM markings required for your specific hazardous zone.