The Allen-Bradley 1771-OBD, also cataloged as the 1771-OBD Digital Output Module, operates as a dedicated hardware component for sourcing 16 discrete DC output signals within PLC-5 chassis backplane networks.

Catalog Number Matrix

Technical Data

Backplane Communication and I/O Density Scaling

The 1771-OBD interfaces with the PLC-5 processor via the 1771 I/O chassis backplane. Backplane bus communication velocity licenses govern data exchange between the adapter module and the processor scan table. I/O density scaling is constrained by chassis slot count and total backplane current budget. Each output point sources current to field devices through the chassis power supply. Firmware flash compatibility between revision B and revision C hardware permits in-chassis replacement without program modification when the processor operating system revision matches the module's electronic keying requirements.

Ordering Information

• 1 x 1771-OBD module (base unit)
• 1 x Installation instruction sheet

Mounting and Wiring

• Install module into any available 1771 I/O chassis slot
• Secure module with chassis mounting latches
• Route field wiring to the removable terminal block
• Verify chassis ground connection before applying power

Frequently Asked Questions

Does the 1771-OBD support hot-swap removal under load?

No. Remove power from the 1771 I/O chassis before extracting or inserting the module. Backplane connectors carry live DC voltage and inductive load energy. Hot-swap operation is not supported by the PLC-5 platform hardware design.

What is the minimum load current requirement per output point?

Each output circuit requires a minimum load current of 2.5 mA to maintain proper transistor saturation. Loads below this threshold may cause incomplete turn-on or erratic switching behavior at the output terminals.

Can the 1771-OBD operate at 24 VDC nominal field supply?

Yes. The operating voltage range spans 10-60 VDC. A 24 VDC field supply is fully within specification. The nominal rating of 48 VDC represents the design center, not an exclusivity limit.

What is the total power dissipation at full 2 A per point load?

Total power dissipation is specified as 15.6 W maximum under full electrical load across all 16 points. Individual point dissipation depends on the voltage drop across the output transistor and the connected load current.

Is the 1771-OBD/B firmware compatible with 1771-OBD/C chassis firmware?

Yes. Firmware flash compatibility exists between revision B and revision C hardware. The processor compares the module's electronic keying data against the I/O configuration file. Mismatched keying triggers a fault if software keying enforcement is active.

What gauge wire is permitted for the terminal block connections?

Use copper wire rated for 60 deg C or 75 deg C. Recommended gauge ranges from 14 AWG to 22 AWG stranded or solid conductor. Torque terminal screws to the manufacturer specification to prevent thermal rise at connection points.

How many modules can be installed in a single 1771 chassis?

Chassis are available in 4-slot, 8-slot, 12-slot, and 16-slot configurations. Total module count is limited by the chassis slot capacity and the power supply's ability to source backplane current for all installed modules simultaneously.

Does the module provide channel-to-channel isolation?

No. All 16 output points share a common internal DC supply rail. Isolation exists only between the backplane logic and the output power circuit. Field wiring must account for this common connection when interfacing with external devices.