Description
Product Introduction & Engineering Value
Intermittent field input problems are often blamed on sensors or PLC processors, yet aging AC input modules can be the real source of nuisance faults. Electrical noise, weak field voltages, or worn terminal connections can cause sporadic input transitions that are difficult to reproduce during troubleshooting.
The Allen-Bradley 1746-IA16 is a 16-channel AC digital input module designed for the SLC 500 platform. It accepts standard 100/120 VAC discrete signals from pushbuttons, selector switches, relays, and limit switches, then transfers the input status across the SLC backplane to the processor for deterministic control. Although discontinued, it remains a widely used replacement module in legacy manufacturing systems.
Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Model | 1746-IA16 |
| Product Family | SLC 500 |
| Product Type | Digital AC Input Module |
| Number of Inputs | 16 |
| Nominal Input Voltage | 120 VAC |
| Operating Voltage Range | 85–132 VAC, 47–63 Hz |
| Points per Common | 16 |
| Nominal Input Current | 12 mA @ 120 VAC |
| Backplane Current Draw | 85 mA @ 5 VDC |
| Maximum OFF-State Voltage | 30 VAC |
| Maximum OFF-State Current | 2 mA |
| Signal Delay | 35 ms ON / 45 ms OFF |
| Isolation | 500 VDC Communication Circuit Isolation |
| Slot Requirement | One SLC 500 Slot |
Field Application & The “Trench” Experience
A grain handling facility reported that conveyor status indicators occasionally remained active after motors had already stopped. Maintenance personnel replaced several proximity switches and even changed the PLC processor, but the problem continued.
During a scheduled outage, technicians monitored the input LEDs on the 1746-IA16 and found that one channel remained intermittently active despite correct field voltage. Replacing the module eliminated the false input transitions immediately, restoring reliable conveyor sequencing without modifying the PLC program.
Typical application scenarios include:
- Conveyor limit switch monitoring
- Motor starter auxiliary contact inputs
- Packaging machine pushbutton stations
- Water treatment valve status monitoring
- Process equipment safety interlock signals
- 1746-IA16
- 1746-IA16
Transparency SOP: QA & Testing
Every New Surplus or professionally Refurbished 1746-IA16 is verified before shipment through a documented inspection process.
- Verify catalog number, serial number, and hardware revision.
- Inspect the PCB, edge connector, and terminal block for damage or overheating.
- Test all sixteen AC input channels using a calibrated 120 VAC source.
- Confirm LED indication and PLC backplane communication.
- Verify isolation integrity and input response timing.
- Complete functional testing in a compatible SLC 500 chassis.
- Package using ESD-safe materials with complete traceability documentation.
The Veteran’s Tech Trap Guide
⚠️ Don’t connect DC signals to this module. The 1746- is designed specifically for 85–132 VAC inputs. Applying DC voltage can result in incorrect operation or permanent module damage.
⚠️ Watch for leakage current from solid-state devices. Some electronic sensors and triac outputs leak enough current to keep an AC input near its switching threshold, causing unexpected ON indications.
PRO TIP: Before replacing the module, measure the input voltage under load rather than with an open circuit. Loose terminals or aging relay contacts often allow voltage to appear normal with a multimeter but collapse once current flows.
PRO TIP: If several adjacent inputs behave erratically, inspect the field common wiring first. A loose common conductor can create symptoms that resemble multiple failed input channels.
Dynamic FAQ
Q1. What is the primary function of the 1746-?
The is a 16-point AC digital input module for the SLC 500 PLC family. It receives 120 VAC field signals and transfers their status to the PLC processor through the SLC backplane.
Q2. What input voltage does the module support?
The module is designed for 85–132 VAC, 47–63 Hz, with a nominal operating voltage of 120 VAC.
Q3. Can the 1746- be used with 24 VDC sensors?
No. This module is intended only for AC input signals. Applications using 24 VDC devices require an appropriate SLC 500 DC input module, such as the 1746-IB series.
Q4. How many field inputs does one module support?
The provides 16 independent AC input channels, occupying one slot in a compatible SLC 500 chassis.
Q5. How is New Surplus authenticity verified?
Each module undergoes catalog verification, visual inspection, isolation testing, functional testing of all sixteen input channels, backplane communication verification, and final operational testing in a compatible SLC 500 rack before shipment.
Q6. Is the 1746- still manufactured?
No. Rockwell Automation discontinued the on November 24, 2022. Existing installations are commonly supported with New Surplus, professionally Refurbished, or repair-tested inventory.
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