A loop detector (or inductive loop detector) is a sensor used to detect the presence of a vehicle, typically installed in the ground near a barrier gate (such as in parking lots, toll booths, or secured entry points). Here’s how it works in conjunction with a barrier gate:

1. Loop Detector Basics

   - The loop detector consists of a coiled wire loop embedded in the road surface.

   - When a metal object (like a car) passes over the loop, it changes the loop’s electromagnetic field.

   - The detector senses this change and sends a signal to the boom gate controller.

2. Interaction with the Boom Barrier Gate

    2.1 Vehicle Detection:  

    - When a car stops or approaches the loop, the detector triggers the gate barrier controller.

    - The controller verifies access (via RFID, ticket, license plate recognition, etc.).

    2.2 Opening the Gate: 

    - If access is granted, the controller activates the barrier gate motor to lift the arm.

    2.3 Vehicle Exit Detection:  

    - Some systems have a second loop after the gate to confirm the vehicle has fully passed.

    - Once the vehicle clears the exit loop, the gate closes automatically (unless another vehicle is detected).

3. Safety & Redundancy

   - Safety Loops: Some systems have additional loops to prevent the gate from closing on a vehicle.

   - Timer-Based Closing: If no vehicle is detected after a set time, the gate closes automatically.

Advantages of a loop detector:

  - Reliable for vehicle detection.

  - Works in harsh weather (unlike optical sensors).

  - Low maintenance once installed.

Disadvantages of a inductive loop detector:

  - Requires cutting pavement for installation.

  - Can be affected by large metal objects (not just vehicles).