Configured for discrete logic execution and input/output control within fixed-configuration architecture, the Allen-Bradley 1747-L20C (1747L20C Processor Unit) provides direct physical/electrical execution across onboard digital channels and DH-485 network loops.

Model Suffix Nomenclature Analysis

• 1747-L20C: Base catalog designation representing a fixed hardware style controller containing 1 K words of memory and AC line power circuitry.
• 1747L20C: Alternative spare parts tracking nomenclature referencing the identical physical processor hardware without embedded license modifications.
• Fixed Hardware Style: Indicates non-modular backplane layout where processor, power supply, and fixed I/O terminals reside on a single integrated printed circuit assembly.

Hardware Specifications

Controller Logic Architecture and I/O Scaling

The processor handles real-time machine automation by executing user ladder logic programs stored within 1 K words of memory. I/O density scaling is fixed to 12 sinking 24 VDC inputs and 8 relay outputs, operating synchronously with firmware routines. DH-485 communication ports facilitate peer-to-peer data exchange and programming terminal connectivity across industrial networks.

Package Ordering Information

• 1 x Allen-Bradley 1747-L20C fixed hardware controller unit
• 1 x Integrated terminal block barrier strip assembly
• 1 x Factory configuration data sheet and jumper documentation

Physical Installation and Wiring Guidelines

• Enclosure Mounting: Secure the controller unit to a flat vertical panel using standard mounting holes, ensuring adequate surrounding air clearance for thermal dissipation.
• AC Power Supply Wiring: Connect line power across the designated 120-240 VAC terminals, ensuring an inline fuse protection limit of 1.25 A is maintained.
• Digital Input Routing: Route 24 VDC sink input wiring separately from high-voltage AC power cables to prevent electromagnetic noise coupling.
• Relay Output Isolation: Adhere strictly to maximum contact rating limits when driving inductive loads, applying suppression diodes or RC snubbers across output terminals.

Frequently Asked Questions

• Does this processor support hot-insertion and removal under power?
  • No, the 1747-L20C features a fixed hardware architecture and must be completely de-energized before performing any wiring or mechanical maintenance.
• What is the native communication protocol used by this controller?
  • The unit utilizes the DH-485 proprietary network protocol for programming downloads and peer-to-peer data transmission.
• Can additional I/O modules be expanded onto this fixed controller?
  • No, fixed hardware style controllers possess a non-expandable base architecture restricted strictly to their onboard 12 inputs and 8 outputs.
• What type of input signal configuration do the digital terminals accept?
  • The 12 digital input channels are configured specifically for 24 VDC sinking device connections.
• What is the maximum line power voltage tolerance for the power supply?
  • The integrated power supply accepts an operational voltage range spanning from 85 to 265 VAC at 47 to 63 Hz frequencies.
• How is user program memory retained when power is removed?
  • User programs are stored in non-volatile memory or backed up via internal battery configurations to prevent data loss during power cycles.
• What current protection is built into the AC power line input?
  • The unit incorporates a power supply fuse protection rating specified at 1.25 A to safeguard internal power circuits.
• Is the controller hardware still actively manufactured by the vendor?
  • No, this unit was officially discontinued by the manufacturer on September 30, 2009, and requires legacy support considerations.