Allen-Bradley 1747-L40C SLC 500 Fixed Hardware Controller

The Allen-Bradley 1747-L40C is a fixed hardware controller within the SLC 500 family designed for standalone machine control and compact industrial automation processes. Incorporating a 120/240 VAC internal power supply, CPU processor with 1K instruction memory, and 40 embedded I/O points into a single panel-mounted assembly, the controller features 24 24 VDC sinking inputs and 16 electromechanical AC/DC relay outputs. It provides localized logic control, integrated high-speed counting capabilities, and direct connectivity across DH-485 network architectures via standard 6-pin terminal connectors.

Integrated I/O and High-Speed Counter Capabilities

The 1747-L40C features 40 embedded I/O channels split between low-voltage DC inputs and flexible relay outputs. The input section comprises 24 24 VDC sinking input channels with 1500 VAC optical isolation, where Input 0 accepts a nominal input current of 20 mA to support high-speed pulse tracking up to 8 kHz, while the remaining 23 inputs draw 8 mA. The output section provides 16 individual AC/DC electromechanical relay contacts suitable for switching variable control voltages across diverse AC and DC field circuits.

Power System and Enclosure Architecture

Operating on an AC line supply of 120/240 VAC, the unit provides an auxiliary 24 VDC user power supply rated at 200 mA to energize external field sensors, switches, or small expansion loads. The fixed housing eliminates the requirement for a main chassis backplane while supporting direct I/O expansion through an optional 2-slot expansion chassis (such as the 1746-A2). Program retention relies on capacitor-backed RAM, which can be augmented with an optional backup battery or non-volatile EEPROM/UVPROM memory modules (e.g., 1747-M11).

Technical Parameters

Frequently Asked Questions

Q: How does the integrated relay output configuration benefit field devices on the 1747-L40C? A: The 16 AC/DC relay outputs act as dry contacts, allowing users to switch different voltage potential levels (both AC and DC) on separate output circuits without needing intermediate interposing relays.

Q: Can the embedded 24 VDC user power supply be used for external components? A: Yes, the controller supplies up to 200 mA at 24 VDC from its internal auxiliary terminals to power sensor loops or small control peripherals.

Q: What expansion options are supported if 40 I/O points are insufficient? A: System hardware capacity can be extended beyond the fixed embedded I/O by adding a 2-slot expansion chassis (such as the 1746-A2) to accept additional 1746 discrete, analog, or specialty I/O modules.