Description
Product Introduction
The Allen-Bradley 1746-IB8 is an 8-point 24V DC sinking digital input module designed for the SLC 500 programmable logic controller system. Installed into any open slot of a 1746 chassis (such as a 1746-A7 or 1746-A10 backplane), the module provides interface connections between low-voltage 24V DC field devices and the logic processing core of the SLC CPU.
Featuring optical isolation between field wiring and backplane circuitry, the 1746-IB8 shields the controller from electrical noise, voltage spikes, and ground loops. Its robust 8-point configuration with a front-mounted LED status array makes it a dependable choice for industrial automation control panels.
Key Technical Specifications
| Parameter | Specification |
| Manufacturer Part Number | 1746-IB8 |
| Number of Inputs | 8 Digital DC Inputs (Sinking) |
| Voltage Category | 24V DC Sink |
| Operating Voltage Range | 10 to 30V DC at 50°C / 10 to 26.4V DC at 60°C |
| Off-State Voltage (Max) | 5V DC |
| On-State Current (Min) | 3.0 mA at 10V DC |
| Nominal Input Current | 8 mA at 24V DC |
| Backplane Current Draw | 50 mA at 5V DC / 0 mA at 24V DC |
| Signal Delay (Max) | Turn-On = 8 ms, Turn-Off = 8 ms |
| Points per Common | 8 Points on 1 Common |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Application Scenarios & The “Trench” Experience
It is 11:30 PM on a high-speed packaging conveyor line. Channel 2 on an input card stops registering signals from a key bottle-jam proximity sensor, causing intermittent false line stops. The maintenance technician suspects an internal optocoupler failure on the module. Thanks to the 1746 removable terminal block (RTB), the tech shuts off panel power, swings the pre-wired terminal arm free without loosening a single field screw, replaces the card with a bench-tested 1746-IB8 from stock, snaps the RTB back on, and powers up—returning the line to automatic mode in less than 5 minutes.
- High-Speed Sensor Tracking – Photoelectric Eyes & Inductive Proxes – Fast 8ms response time allows accurate part sensing on fast-moving conveyors.
- Safety & Interlocking Circuits – Pushbuttons & Guard Switches – Reads 24V DC dry contacts, selector switches, and auxiliary safety relay contacts.
- Legacy Panel Maintenance – SLC 5/03, 5/04, 5/05 Systems – Replaces worn or damaged DC input channels in existing control cabinets.
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; every 1746-IB8 module undergoes strict diagnostic bench testing prior to dispatch.
- Inbound Physical & Terminal Audit: Checked housing plastics, backplane edge connector pins, and terminal block screw threads for signs of wear or corrosion.
- Backplane Logic Verification: Installed into an active 1746-A10 rack; confirmed 50 mA backplane current draw and CPU detection without backplane communication errors.
- 8-Channel Input Signal Testing: Applied 24V DC inputs across each of the 8 channels individually; verified LED illumination and RSLogix 500 input data table updating (
I:e.0throughI:e.7). - Off-State Threshold Check: Verified that voltages below 5V DC correctly register as OFF to ensure immunity against stray field noise.
- ESD Protection & Packaging: Cleaned, wrapped in antistatic shielding wrap, and packaged inside shock-absorbing foam containers.
- 1746-IB8
- 1746-IB8
The Veteran’s Tech Trap Guide (Crucial Value-Add)
- ⚠️ Sink vs. Source Wiring (Sourcing Sensors Required)!
The 1746-IB8 is a sinking input module (current flows into the module terminals). This means connected 3-wire DC sensors must be PNP (sourcing) outputs, which switch +24V DC to the input terminal. Connecting NPN (sinking) sensors will not trigger the input circuit. (For NPN sensors, use a sourcing input card like the 1746-IV8).
- ❗ Never Hot-Swap Modules in a 1746 Chassis!
Like all SLC 500 components, inserting or removing the 1746-IB8 while rack power is applied will cause electrical arcing, potential memory corruption, or permanent damage to backplane driver ICs. Always isolate main rack power prior to swapping modules.
- ⚠️ Common Terminal Polarity
All 8 input channels share a single common return line (Terminal 9). For sinking inputs, the DC Common (0V DC) must be connected to Terminal 9 to complete the 24V DC input circuit loop.
- ❗ Temperature Derating at 60°C
If operating in hot enclosures near the 60°C (140°F) ambient limit, the maximum field input voltage range drops from 30V DC down to 26.4V DC to prevent internal thermal overload.
Frequently Asked Questions (FAQ for Conversion)
Q: What is the difference between 1746-IB8 and 1746-IB16?
A: The 1746-IB8 provides 8 digital 24V DC inputs on 1 common terminal, while the 1746-IB16 provides 16 digital 24V DC inputs on 1 common terminal in the same single-slot module footprint.
Q: Can I use AC signals on a 1746-IB8 module?
A: No. The 1746-IB8 is strictly designed for 10–30V DC signals. Connecting 120V AC will destroy the module’s input circuits. For 120V AC signals, use a 1746-IA8 or 1746-IA16 card instead.
Q: Does the module include the removable terminal block (RTB)?
A: Yes, all our New Surplus and Refurbished 1746-IB8 modules come complete with the front removable terminal block assembly.
Q: Are 1746-IB8 modules still manufactured by Allen-Bradley?
A: The SLC 500 platform has matured into legacy/discontinued status by Rockwell Automation. We maintain extensive stock of certified New Surplus and fully bench-tested, refurbished original 1746-IB8 modules.
Q: What warranty is provided with this module?
A: Every Allen-Bradley 1746-IB8 input module includes a full 12-month replacement warranty. If any input channel or backplane interface fails under standard operating conditions within one year, we send an immediate replacement from stock.
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