Allen-Bradley 1746-ITB16

The Allen-Bradley 1746-ITB16 is a high-speed, 24V DC digital input module for the SLC 500 PLC series. It features 16 points and is categorized as a Sinking (NPN) input module.

Because it is a “Fast Response” module, it is typically used for high-speed switching applications where standard input modules (like the 1746-IB16) would be too slow to capture the signal.

1. Key Technical Specifications

The “T” in ITB16 stands for Fast Response, meaning it has much shorter hardware filter times than standard modules.

2. Sinking vs. Sourcing Logic

It is critical to understand that the 1746-ITB16 uses Sinking logic.

• The Module: Sinks current to the DC common (Ground).

• The Sensor: Must be a Sourcing (PNP) sensor.

Wiring Logic: You connect the positive side (+24V) to your switch or sensor. When the sensor is triggered, it sends the +24V into the ITB16 terminal. The module then “sinks” that signal to the common return.

3. Terminal Layout and Wiring

The module uses a standard removable 18-point terminal block.

• Terminals 0–7: First 8 input points.

• Terminal 9: VDC (Common for the first group).

• Terminals 10–17: Last 8 input points.

• Terminal 18: VDC (Common for the second group).

4. Fast Response Applications

Standard PLC inputs have a “de-bounce” filter that ignores signals shorter than 8 milliseconds to prevent electrical noise from being read as a button press.

The 1746-ITB16 reduces this to 0.3 ms. Use this module for: