High-performance photosensors and fiber optic sensors

How fiber optic sensors work for object detection

Sensors for Presence control/object detection are used in a wide variety of industrial processes and are among the most widely used industrial sensor technologies worldwide. Optical measurement technologies play a key role in many application areas and are used wherever non-contact measurements are required and the sensor cannot be placed in the immediate vicinity of the measurement object. In fiber optic systems, optical sensors are used in conjunction with fiber optic cables, which allow all electronic components to be placed away from the measurement point.

There are different operating principles available for optical sensors for presence control:

• light switch

These operate on the reflection principle: The transmitter and receiver units are integrated into one device. The receiver unit measures the intensity of the emitted and reflected light. If the set threshold is exceeded, the presence of the target object is determined. The sensor therefore acts, in a sense, like a light/dark switch.

In conjunction with suitable light guides, fiber optic light sensors can also be implemented for hard-to-reach measuring points, harsh environmental conditions or even ATEX environments.

•  One-way light barriers

With light barriers, the transmitting and receiving units are separated from each other and are placed opposite each other - the light emitted by the transmitter is detected directly by the receiver and thus forms the “light barrier” that gives it its name. If this light beam is interrupted by an object, the receiver receives no light and switches the output.

Depending on the application conditions, light barriers can be implemented with or without a light guide (fiber-optic light barrier). For fiber optic light barriers, it should be noted that fiber optics with two separate arms must be used.

• Collision protection sensors

Our collision protection sensors for overhead cranes are a special feature among the optical sensors for presence monitoring: They work like reversed light barriers that are open during operation and are only closed when the two cranes approach each other. Our crane collision protection sensors are characterized by self-monitoring and particularly long ranges.

• Passive sensors

Passive sensors are another special type of optical sensor: These do not have their own light source, but rather evaluate the radiation from external light sources. In normal operation, the passive sensor detects only low light intensities. Only when an object with high emission (e.g., due to high temperatures) enters the detection range, and the light intensity received by the sensor exceeds the set threshold, does the sensor switch on.

We primarily use these sensors to detect glowing metals or flashes of light; due to the high temperatures involved, they are usually fiber-optic systems.

• Reflection light barriers

Retro-reflective sensors are another special form of optical sensors and consist of a reflex light sensor that creates a light barrier with an opposing reflector or mirror. However, due to the often susceptibility of the reflectors to dirt or higher temperatures, we do not offer them.