In focus: Festo sensors

Increased cycle times, better process control, shorter downtimes: these days system and machine management that ensures the optimal use of resources is a critical factor in the economic success of a company. Sensor technology, too, is an indispensable part of this success in the world of automation. The purpose of an optical sensor is to measure a physical quantity of light in a high speed and, depending on the type of sensor, then translates it into a form that is readable by an integrated measuring device.

High quality for smooth processes

Optimum performance and maximum reliability: our comprehensive portfolio of sensors combines these important core qualities and ensures smooth and efficient production sequences in different medical applications for example.

The full range

From the position sensor SMAT to pressure sensing with the pressure sensor SPAN and flow sensing with the flow sensor SFAH, our product portfolio covers the full range of classic sensor tasks for pneumatics. In addition, Festo offers sensors such as the sensor that have been developed for precise and reliable contact sensing and special tasks. The new electronic proximity switch SDBT-MSX is the first proximity sensor with automatic switching point adjustment.

Optical sensors

Thanks to their optical measuring method, the sensor series covers a wide range of different functions, from detecting color and miniature components through to laser distance sensing.

Diffused sensors detect objects when the light beam, emitted towards the target, is reflected back to the sensor by the target. What makes diffused sensors a great automation option is that they are more compact than typical units, as all components are in a single housing.

Optoelectronic sensors detect objects with light of a part of the spectrum to trigger function to control, to switch or to regulate. Electrical impulses are converted into light impulses by the transmitter of the optoelectronic sensor and back into a electrical signal by the receiver. The amplifier circuit with downstream comparator processes and compares the signal with a default treshold. The switching function of the output amplifier is triggered depending on the interruption of the beam path. Exact positioning and very large sensing ranges can be achieved with optoelectronic sensors, independent from the material of the objects to detect.

What are electro-optical sensors?

Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. These sensors are able to detect electromagnetic radiation from the infrared up to the ultraviolet wavelengths. They are used in many industrial and consumer applications. Most common types:

• Lamps that turn on automatically in response to darkness
• Position sensors that activate, have high sensitivity, when an object interrupts a light beam
• Flash detection, to synchronize one photographic flash to another
• Photoelectric sensor that detects the distance, absence, or presence of an object.
• We see ambient light sensors on our mobile handsets.

Function of optical sensor

An optical sensor converts light rays into digital signal. It measures the physical quantity of light and then translates it into a form that is readable by an instrument. An optical sensor is generally part of a larger system that integrates a source of light, a measuring device and the optical sensor. This is often connected to an electrical trigger. The trigger reacts to a change in the signal within the light sensor. An optical sensor can measure the changes from one or several light beams. When a change occurs, the light sensor operates as a photoelectric trigger and therefore either increases or decreases the electrical output.

There are many different types of optical sensors suitable:

Photoconductive devices convert a change of incident light into a change of resistance.

Photovoltaics, commonly known as solar cells, convert an amount of incident light into an output voltage.

Photodiodes convert an amount of incident light into an output current.

Phototransistors are a type of bipolar transistor where the base-collector junction is exposed to light. This results in the same behavior of a photodiode, but with an internal gain.

Optical Switches are usually used in optical fibers, where the electro-optic effect is used to switch one circuit to another. These switches can be implemented with, for example, microelectromechanical systems or piezoelectric systems.

Common applications

• Electro-optical sensors are used whenever light needs to be converted to energy. Because of this, electro-optical sensors can be seen almost anywhere. Common applications are smartphones where sensors are used to adjust screen brightness, and smartwatches in which sensors are used to measure the wearer's heartbeat.

• Optical sensors can be found in the energy field to monitor structures that generate, produce, distribute, and convert electrical power. The distributed and nonconductive nature of optical fibres makes optical sensors perfect for oil and gas applications, including pipeline monitoring. They can also be found in wind turbine blade monitoring, offshore platform monitoring, power line monitoring and downhole monitoring. Other applications include the civil and transportation fields such as bridge, airport landing strip, dam, railway, airplane, wing, fuel tank and ship hull monitoring.
• Among other applications, light sensors can be found in thermal methods which vary the refraction index in one leg of an interferometer in order to switch the signal, MEMS approaches involving arrays of micromirrors that can deflect an optical signal to the appropriate receiver, piezoelectric beam steering liquid crystals which rotate polarized light depending on the applied electric field and acousto-optic methods which change the refraction index as a result of strain induced by an acoustic field to deflect light.

Another important application of optical sensor is to measure the concentration of different compounds by both visible and infrared spectroscopy.