Specifying Fiber Optic Sensors

The industry prefers fiber optic sensors as they work well in tight spots and in applications that have a high degree of electrical noise. Fiber optic sensors are useful in machines, fixtures, and conveyors for sensing part presence as an important component of industrial automation. The industry often requires controlling sequence and error-proofing assembly based on the presence or absence of a part. In many cases, it is simply impossible to know whether a part is where it should be or the holder is empty as expected. Therefore, verification is only possible by using a presence sensor.

Sensors come in many varieties, including magnetic, capacitive, inductive, and photoelectric. Depending on the application, each type of sensor has its own merits and demerits. Among all the sensors available in the market, photoelectric sensors offer the broadest types and technologies, and suitable for the widest range of applications.

The family of photoelectric sensors includes a large variety of light-emission types that includes lasers of class 1 and 2, visible, and infrared. They also include different sensing technologies such as through-beam, reflective, suppression, background, and diffuse. Different housing configurations are also available such as fiber optics and photo eye. We will focus on specifying and applying fiber-optic sensors, as these offer the most advanced capabilities with options for configuration, and are most suitable for use in tight spots that the photo-eye sensor finds too small.

Fiber-optic sensors are also known as fiber photoelectric sensors, and comprise of two parts—the amplifier and the fiber cable. The amplifier is the electronic part and is actually a fiber photoelectric amplifier. The fiber-optic cable includes the optic sensor head and the fiber cable to transmit light to and from the amplifier.

All photoelectric sensors work with a simple technique. A light emitter produces the source signal and a receiver detects the signal. A large variety of technologies is available for sensing and measuring the light transmitted to the receiver. For instance, standard photo-eyes look for the presence or absence of light, whereas background suppression sensors sense the angle of the returning beam. Other type of sensors measure the time taken by the light to return, thereby providing a measure of distance it traveled.

Simple photo-eyes such as those used in reflective and diffuse units house the emitter and receiver in the same optical sensor head, while through-beam units house them in two optical sensor heads. On the other hand, fiber-optic sensors have all the electronics in a single housing, with a fiber cable connecting the separate emitter and receiver to the electronic housing. Light from the emitters and that coming to the receivers travels through the fiber cables, similar to high-speed data traveling through fiber-optic networks.

The above segregation means the technician has to mount only the sensor head on the machine, while routing the integrated fiber-optic cable and plugging it into the amplifier placed in a safe place such as a control enclosure to protect it from the harsh manufacturing environment.

A large variety of options is available for both fiber-optic cables and amplifiers. These range from basic to advanced, suitable for meeting the demands of increasing functionality, including advanced logic and communication capabilities.