Description
Product Introduction & Engineering Value
A digital input module rarely gets attention until a production line begins stopping for reasons that cannot be explained. False sensor signals, intermittent switch inputs, or unstable field wiring often appear to be PLC faults when the real issue is the input interface itself.
The Allen-Bradley 1746-IB16 is a 16-point sinking DC input module for the SLC 500 PLC platform. It accepts 24 VDC discrete signals from proximity sensors, photoelectric sensors, pushbuttons, and relay contacts while providing electrical isolation between field devices and the controller backplane. It remains a common replacement module for maintaining legacy SLC 500 installations.
Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Model | 1746-IB16 |
| Product Family | SLC 500 |
| Product Type | Digital DC Input Module |
| Number of Inputs | 16 |
| Input Type | Sinking DC |
| Nominal Input Voltage | 24 VDC |
| Operating Voltage Range | 10–30 VDC |
| Points per Common | 16 |
| Nominal Input Current | 8 mA @ 24 VDC |
| Backplane Current Draw | 85 mA @ 5 VDC |
| Maximum OFF-State Voltage | 5 VDC |
| Maximum OFF-State Current | 1 mA |
| Maximum Signal Delay | 8 ms ON / 8 ms OFF |
| Isolation | 500 VDC Communication Circuit Isolation |
| Slot Requirement | One SLC 500 Chassis Slot |
Field Application & The “Trench” Experience
A pallet conveyor system began stopping randomly because cartons were reported at transfer stations even when no product was present. Maintenance personnel replaced two proximity sensors and rewired several junction boxes, yet the false inputs continued.
During troubleshooting, engineers monitored the input LEDs on the 1746-IB16 while measuring field voltage. One channel occasionally remained active even after the sensor output dropped to zero. Replacing the input module eliminated the intermittent signal without requiring PLC program changes or sensor replacement.
Typical application scenarios include:
- Conveyor photoelectric sensor monitoring
- Packaging machine limit switch inputs
- Automated storage and retrieval systems
- Assembly line presence detection
- Material handling safety interlock monitoring
- 1746-IB16
- 1746-IB16
Transparency SOP: QA & Testing
Every New Surplus or professionally Refurbished 1746-IB16 undergoes a documented verification procedure before shipment.
- Verify catalog number, serial number, and hardware revision.
- Inspect the PCB, edge connector, and terminal interface for physical damage.
- Test all 16 input channels using a calibrated 24 VDC source.
- Verify LED status indicators and SLC backplane communication.
- Confirm input response time and electrical isolation.
- Perform operational testing in a compatible SLC 500 chassis.
- Package using anti-static, impact-resistant materials with full traceability.
The Veteran’s Tech Trap Guide
⚠️ Remember that this is a sinking input module. It is intended to receive signals from sourcing (PNP) field devices. Incorrect sensor selection is one of the most common causes of commissioning problems.
⚠️ Don’t ignore leakage current. Some solid-state outputs leak enough current to illuminate the input LED or produce intermittent PLC input status even when the field device appears to be OFF.
PRO TIP: If several adjacent inputs begin behaving erratically, inspect the common return wiring before replacing the module. A loose DC common often produces symptoms that resemble multiple failed input channels.
PRO TIP: Before installing a replacement module, inspect the backplane connector for bent pins or contamination. Field experience shows that damaged chassis contacts can produce intermittent communication issues that are easily mistaken for a defective input card.
Dynamic FAQ
Q1. What is the primary function of the 1746-?
The 1746- is a 16-point DC digital input module that receives discrete 24 VDC field signals and transfers their status to an SLC 500 processor through the chassis backplane.
Q2. What input voltage does the module support?
The module accepts 10–30 VDC sinking input signals, with 24 VDC being the nominal operating voltage.
Q3. What types of field devices are typically connected?
The 1746- is commonly used with PNP proximity sensors, photoelectric sensors, limit switches, pushbuttons, relay contacts, and other 24 VDC sourcing output devices.
Q4. Is the 1746- compatible with every SLC 500 chassis?
Yes. The module occupies one slot in any compatible 1746-series SLC 500 chassis and communicates through the standard SLC backplane.
Q5. How is New Surplus authenticity verified?
Each module is inspected for catalog number accuracy, connector condition, isolation integrity, LED functionality, backplane communication, and successful operation of all sixteen input channels before shipment.
Q6. Is the 1746- still manufactured?
No. Rockwell Automation discontinued the on December 31, 2021. It is now primarily available as New Surplus, professionally Refurbished, or repair-tested inventory for supporting legacy SLC 500 systems.
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