PLC current sinking input module

Show a diagram of a typical input for a current sinking input module.

A PLC current sinking input module, also known as a “sinking input module” or “NPN input module,” is a type of input module used in Programmable Logic Controllers (PLCs) to interface with devices that provide a current sinking output signal.

Let’s understand how it works:

  1. Current Sinking Input: In industrial control systems, devices like switches, sensors, and proximity sensors often have current sinking output configurations. In a current sinking configuration, the output device acts as a current sink, meaning it allows current to flow into it when activated.
  2. Sinking Input Module: A sinking input module is designed to interface with devices that provide a current sinking output. The module is connected to the PLC’s input rack and receives the current sinking signal from the external devices.
  3. Connection and Wiring: To interface with a current sinking device, the positive (+) terminal of the external device is connected to a positive voltage supply (Vcc), typically provided by the PLC’s power supply. The negative (-) terminal of the device is then connected to the input terminal of the sinking input module. This completes the current path from the positive voltage supply through the device and into the input module.
  4. Input Signal Detection: When the external device is activated, such as a switch closing or a sensor detecting an object, current flows through the device and into the input module. The sinking input module detects this current flow and interprets it as an “ON” or logic “1” state.
  5. PLC Programming: In the PLC program, the sinking input module is typically assigned to a specific input address or channel. The program can then monitor the status of that input address and execute corresponding control logic based on its state (ON or OFF).

It’s important to note that sinking input modules are designed to work specifically with current sinking devices. If the external device has a current sourcing output configuration (current sourcing devices allow current to flow out of them when activated), a current sourcing input module (also known as a sourcing input module or PNP input module) would be required.

When selecting input modules for a PLC, it’s essential to match the input module type (sinking or sourcing) with the output configuration of the connected devices to ensure proper signal detection and compatibility.