Allen-Bradley 1746-OB8 SLC 500 Digital I/O Modules

The Allen-Bradley 1746-OB8, also cataloged as the 1746-OB8 Digital DC Output Module, operates as a dedicated hardware component for discrete current-sourcing execution within SLC 500 platforms.

Hardware Specifications

Industrial Control & Drive Integration

The 1746-OB8 synchronizes signal sequencing according to the backplane bus communication velocity limitations of the legacy SLC chassis. Deployed alongside network scanning interfaces, it coordinates localized I/O density scaling profiles within Profinet / EtherNet/IP deterministic networks. Maintaining consistent firmware flash compatibility between peripheral communication adapters and the central processor is necessary to guarantee accurate mapping of the 8-point sourcing register without causing packet update failures or circuit propagation lag.

Frequently Asked Questions

Q: Does the 1746-OB8 module allow Online Insertion and Removal (OIR) under backplane electrical load?

A: No. The SLC 500 rack structure does not support hot-swapping or Removal and Insertion Under Power (RIUP). Prior to removing or inserting this card into the chassis slot, the primary power supply powering the backplane must be completely isolated to avoid corrupting data registers or causing electrical degradation.

Q: How do environmental conditions affect the output current capacity of the 1746-OB8?

A: The continuous current limit per output is strictly constrained by linear thermal derating curves. At an internal ambient temperature of 30 deg C, each channel supports 1.0 A continuous load; this rating drops directly to 0.50 A per channel when operating at the maximum upper limit of 60 deg C.

Field Installation Guidelines

• Chassis Slot Insertion: Power down the assembly. Align the printed circuit board side rails with the top and bottom chassis slot grooves, pushing the module until the mechanical locking retention tabs latch firmly into the frame.
• Sourcing Field Connections: Connect the external 10-50 VDC supply positive lead to the common rail of the removable terminal block. Ensure that all field actuators are landed to their corresponding terminal outputs, observing proper wire gauge to handle high continuous current loads.
• Grounding Protocols: Verify that the SLC 500 chassis frame is connected directly to a low-impedance functional earth ground grid. Separate discrete DC signal loops from concurrent AC inductive power conduits to suppress high-frequency electromagnetic noise injection.