Allen-Bradley 1771-OBD/C 1771 PLC-5 I/O System Digital Output Module

The Allen-Bradley 1771-OBD/C, also cataloged as the 1771-OBD Digital Output Module, operates as a dedicated hardware component for controlling external devices within 1771 PLC-5 I/O System platforms.

Hardware Specifications

Profinet / EtherNet/IP Deterministic Networks and I/O Density Scaling

The 1771-OBD/C handles 16 independent solid-state DC load drivers to maximize local I/O density scaling inside standard 1771 universal racks. To maintain synchronous operational sequencing over Profinet or EtherNet/IP deterministic networks via an adapter module, the 1771-OBD/C restricts its internal backplane bus logic consumption to 400 mA at 5 VDC. This strict boundary optimizes the chassis power margin, allowing proper firmware flash compatibility across legacy systems and preventing bus execution dropouts during dense channel switching events.

Frequently Asked Questions

Q: What is the total combined electrical current limit for the 1771-OBD/C module?

A: The cumulative electrical current across all 16 channels must not exceed 8 A total for the module, even though individual discrete channels can handle up to a 2 A maximum resistive load.

Q: Does the 1771-OBD/C possess internal short-circuit protection for its channels?

A: No. The internal electronic circuitry lacks embedded individual fuses. External fuse protection per output channel is necessary to guard the internal switching components against overcurrent states.

Q: Is online hot-swapping supported for this module inside an energized 1771 chassis?

A: No. The physical architecture of the 1771 rack requires isolation and complete power de-energization prior to module removal or insertion to protect against backplane logic faults and component stress.

Field Installation Guidelines

• Chassis Alignment: Align the module side tracks with the upper and lower plastic guides of the 1771 chassis slot. Slide the module backward until it sits completely into the backplane bus socket.
• External Circuit Protection: Wire external inline fast-acting fuses for each channel to safeguard the module from field-side short-circuits.
• Inductive Load Suppression: Install a flyback diode in parallel across DC inductive loads, such as solenoid coils and DC relays, to absorb transient voltage spikes during module turn-off cycles.
• Conductor Separation: Maintain physical isolation between the low-voltage DC output signal wires and any adjacent high-voltage AC electrical distribution or motor control cables.