Allen-Bradley 1756-OB16 ControlLogix Digital Output Module

The Allen-Bradley 1756-OB16, also cataloged as the 1756-OB16 Digital Output Module, operates as a dedicated hardware component for high-density discrete load switching within ControlLogix chassis platforms. The unit executes direct electronic switching across 10-30 VDC sourcing output circuits to drive industrial solenoids, relays, and field indicators. Integrated hardware circuitry provides channel-to-bus galvanic isolation, preventing field-side voltage transients from compromising backplane communication logic and processing hardware.

Hardware Specifications

ControlLogix System Architecture & Backplane Bus Velocity

The module interfaces directly with the local ControlLogix backplane using high-velocity CIP (Common Industrial Protocol) messaging framing. Backplane bus communication velocity enables rapid, deterministic updates of output point states synchronized with the controller scan cycle. Scalable I/O density features allow multiple 16-point output modules to co-exist within a single rack assembly without degrading backplane throughput. Firmware flash compatibility ensures seamless firmware maintenance and platform integration via Studio 5000 Logix Designer software.

Frequently Asked Questions

Q: Does the 1756-OB16 support Removal and Insertion Under Power (RIUP)?

A: Yes, the module can be removed or inserted while the backplane chassis is powered. However, power supply to the field-side Removable Terminal Block (RTB) must be isolated prior to hardware removal to prevent electric arcing and contact damage on terminal pins.

Q: How is field wiring power isolated from internal controller logic on the 1756-OB16?

A: Internal optical isolators separate the 5.1 VDC backplane logic circuitry from the external 10-30 VDC field power supply, providing continuous isolation between backplane communications and field-side wiring loops.

Field Installation Guidelines

• Connect chassis ground lug directly to the enclosure star ground point using short, heavy-gauge copper conductors to satisfy IEEE 1100 industrial grounding requirements.
• Ensure the 20-pin Removable Terminal Block (RTB) locking latches click securely into the top and bottom chassis keyways before applying field power.
• Maintain physical separation between 24 VDC output wiring and high-voltage AC conductors within panel cable ducting to reduce inductive crosstalk.
• Install external surge suppression devices, such as flyback diodes, across inductive DC loads to clamp reverse inductive voltage spikes during switching transitions.