Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | 1746-IB8 |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Product Type | 8-Point DC Input Module (Sinking / NPN) |
| PLC Family | SLC 500 |
| Number of Inputs | 8 (single group, non-isolated) |
| Input Type | Current Sinking (NPN) |
| Input Voltage Range | 10–30V DC |
| Nominal Input Voltage | 24V DC |
| ON State Voltage | 10–30V DC |
| OFF State Voltage | 0–3V DC |
| ON State Current | 8 mA @ 24V DC (typical) |
| OFF State Current | 1.5 mA maximum |
| Current Limit per Point | 0.125A |
| OFF-to-ON Response | 3 ms maximum |
| ON-to-OFF Response | 1 ms maximum |
| Isolation | 500V AC dielectric (field to logic) |
| Backplane Current Draw | 0.085A @ 5V DC |
| Operating Temperature | 0°C to +60°C |
| Storage Temperature | -40°C to +85°C |
| Dimensions (W×H×D) | 55.9 mm × 131.1 mm × 101.6 mm |
| Weight | Approx. 210 g |
| Mounting | 1746 Chassis / Card Rack (Slot-based) |
| Connection Type | Screw terminal (requires 1746-N2 or 1746-N3 terminal block) |
| Wire Size | 22–14 AWG solid or stranded |
| Ingress Protection | IP20 (enclosed cabinet use) |
Main Features and Advantages
The Allen-Bradley 1746-IB8 delivers dependable DC input acquisition through a combination of well-engineered hardware protection and straightforward operating characteristics. Its sinking input design is the natural complement to NPN proximity sensors and three-wire DC sensors, which remain the dominant field device type in North American manufacturing. Each of the eight inputs sources current from the field device and returns it through the module’s common connection, creating a simple, predictable wiring scheme that technicians can troubleshoot with a basic multimeter.
Protection is built into every channel of the Allen-Bradley 1746-IB8. The back-to-back diode arrangement across each input protects against reverse polarity connections—a common wiring error that destroys unprotected input circuits. This feature alone prevents a significant percentage of field-induced module failures. The 0.125A current limit per point provides a second layer of defense, restricting fault current even if a field device shorts or a wiring error applies excessive voltage. Together with the 500V AC optical isolation between field and logic sides, these protections create a robust input front end capable of surviving the electrical noise, transient spikes, and accidental miswiring that characterize real-world industrial installations.
The response time specification of the Allen-Bradley 1746-IB8 is carefully matched to discrete control requirements. At 3 ms OFF-to-ON and 1 ms ON-to-OFF, the module is fast enough for high-speed counting applications and rapid machine sequencing, yet slow enough to reject contact bounce and electrical noise that would otherwise generate false inputs. This deliberate filtering characteristic means that applications work reliably without additional debounce programming in most cases. The visual status indicators on the front of the module provide immediate feedback during commissioning and troubleshooting, allowing technicians to distinguish between sensor failures, wiring problems, and logic faults without software tools.