Safety I/O Modules | Allen-Bradley 1791DS-IB8XOBV4

The 1791DS-IB8XOBV4 is a 24 VDC DeviceNet Safety combination I/O block in the Allen-Bradley CompactBlock Guard I/O family. Designed for distributed safety control applications, it integrates 8 safety inputs, 8 test pulse outputs, and 4 solid-state dual-channel bipolar safety outputs into a compact housing. The module communicates using the CIP Safety protocol over DeviceNet Safety networks to achieve SIL 3 (IEC 61508) and Category 4 / PLe (ISO 13849-1) compliance.

Safety Input and Bipolar Output Architecture

The input section of the 1791DS-IB8XOBV4 features 8 current-sinking safety inputs configurable for single- or dual-channel safety devices such as e-stops, safety switches, and light curtains. 8 dedicated test pulse outputs supply field contact power while injecting low-duration test pulses to detect short-circuits to 24 VDC and cross-faults. On the output side, 4 solid-state bipolar outputs pair current-sourcing (P-side) and current-sinking (M-side) switches per channel, providing short-circuit protection and reliable line fault detection for safety actuators.

DeviceNet Safety Communication and Field Setup

DeviceNet Safety integration enables seamless exchange of safety input/output status, configuration settings, and detailed diagnostic information over a single network trunkline. Safety Network Numbers (SNN) and node address assignments are configured using DeviceNet configuration tools or RSNetWorX for DeviceNet. The module mounts on a standard 35 mm DIN rail and features removable terminal blocks alongside front-panel LEDs for power, network status, module health, and individual channel status.

Frequently Asked Questions

Q: How does the bipolar output configuration on the 1791DS-IB8XOBV4 protect output loads? A: Bipolar outputs control both the 24 VDC sourcing side and the 0 VDC sinking side of the load simultaneously. If a short circuit to power or ground occurs on either leg, the module opens the opposite side to safely interrupt power to the connected device.

Q: Can the 8 test outputs be used as standard control outputs? A: No, the 8 test pulse outputs are specifically designed to power safety field contacts and generate pulse signals for short-circuit detection; they cannot be used as general-purpose control outputs.