What is the difference between reflective fiber sensors and through‑beam fiber sensors?

Reflective fiber sensors and through‑beam fiber sensors are common types of fiber sensors used to detect light transmission or changes. Both sensors consist of optical fibers and light sources, but their working principles and application scenarios differ. In this article, the Atonm technical editor introduces the differences between these two sensors and examines their advantages and disadvantages in their respective application fields.

1. Reflective fiber sensors

Reflective fiber sensors use an optical fiber as the sensing element to detect the intensity of light reflected at the fiber end. This allows them to determine the position, shape, and size of the target object. A reflective fiber sensor typically includes a light emitting diode (LED) and a receiving fiber. When an object enters the sensor area, it reflects light back into the receiving fiber, causing the received signal to change. The sensor processes this signal change to determine the target information.

The advantage of reflective fiber sensors is that they can work in various environments such as dust, fog, or rain because they detect reflected light rather than relying on long distance light transmission. Reflective sensors are also suitable for detecting low‑reflectivity or irregularly shaped targets such as metal sheets, plastic, or glass. In general, reflective fiber sensors are simpler and less expensive than through‑beam types.

Their limitation is that they only detect targets close to the fiber end because reflected light must bounce back to the fiber tip to be detected. This makes them unsuitable for long‑range detection and often requires placing the fiber near the target. If the target has low reflectivity or a rough surface, the reflected signal may be very weak, causing detection failures.

2. Through‑beam fiber sensors

Through‑beam fiber sensors transmit light from a source to a receiver using optical fibers. They usually consist of two fibers and two light sources placed at opposite ends of the detection area in a transmitter‑receiver configuration. When an object passes through the detection zone, it blocks the light beam and the change is detected by the receiver, allowing the sensor to determine the object position and shape.

The advantage of through‑beam sensors is that they can detect objects at longer distances because detection range depends on the separation between the two fibers rather than the distance to the fiber end. They can also detect targets on reflective surfaces such as metal or glass since they rely on beam interruption rather than reflection strength.

However, through‑beam sensors require more precise installation and alignment of the two fibers, which increases installation and calibration complexity. They are typically more expensive and can be affected by dust, fog, or rain.

In summary, reflective fiber sensors and through‑beam fiber sensors each have unique strengths and weaknesses. Choose the sensor type according to the application: reflective sensors for low‑reflectivity or irregular targets and harsh environments; through‑beam sensors for longer distance detection and reflective surfaces.