Fibre Optic Sensors
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Amplifier series with high clarity “ OLED” display, easy to use operation, and TERA power.
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The new MEGA-Power, MEGA-Easy and MEGA-Stable FS-V30 digital fibre optic sensor. High power beam for stable detection in harsh environments.
A fibre optic sensor is an instrument that measures light from an LED (or other device) for detection purposes. These devices are most commonly used in factory automation environments.
Fibre optics feature two distinct components, an amplifier and sensor heads. The amplifier contains "the brains" of the sensor as well as the light source. The fibre optic cables/heads are used solely to transmit and receive the light.
Because there are no electronic components in the sensing heads, fibre optic sensors are commonly used in tight spaces, harsh environments, or simply where other sensors cannot be used.
Principles of fibreoptic sensors
Fibre optic sensors detect target conditions by transmitting light onto or across a target and measuring the increase or decrease of light returned.
Optical principles of fibreoptic sensors
The properties of light include straightness, refraction, and reflection. Fibreoptic sensors utilise these properties to enable various types of detection.
Specular reflection and retro-reflection
Specular reflection is reflection where the angle of incidence and angle of reflection of light are the same on a flat surface such as a mirror or glass. Retro-reflection is reflection where light projected at two reflective surfaces mounted at right angles is reflected off both surfaces and travels in the opposite direction of the incident light.
Refraction
Light normally travels straight through air or water. However, if the light passes through a boundary surface between materials with different refractive indices, the direction of travel changes. This phenomenon is referred to as refraction.
Polarisation
Light waves normally oscillate in a variety of directions. Polarisation is when oscillation is limited to one direction. Devices that restrict the oscillation direction are called polarising filters. However, polarising filters that restrict oscillation in a specific direction will block light which oscillates in the perpendicular direction.
Detection principles of fibreoptic sensors
There are several types of fibre optic sensors. Detection methods include thrubeam, reflective, retro-reflective and definite-reflective. Each method is used for different applications and targets.
Thrubeam models
Thrubeam models include a transmitter and receiver installed opposite each other. As the target passes between the transmitter and receiver, light is blocked and detection is performed by determining the decrease in the received light intensity. Detecting distances range from a couple of inches to several feet. Stability is achieved with high resistance to dirt and dust. Opaque targets can be detected regardless of reflectance, colour, or material.
Reflective models
With reflective models, light emitted from a transmitter hits the target and the reflected light is returned to the receiver. Target detection is based on the amount of reflected light returned to the receiver. Because the detecting distances range from a couple of inches to several metres, adjustment during installation is incredibly easy. Detection is possible even for small targets.
Retro-reflective models
Retro-reflective models detect the amount of light returned from a reflector installed opposite of the transmitter. The light from the reflector is blocked as a target passes through, reducing the amount of received light. Targets are detected by measuring this reduction. Installation is easy with detecting distances ranging from a couple of inches to several feet. Detection is also less likely to be affected by target colour or angle, and opaque targets can be detected regardless of shape, colour, or material.
Definite-reflective models
In definite-reflective models, light is sent and received at a specific angle creating an intersecting point at a fixed distance. This ensures detection is performed only where the optical axes intersect. These models are often used when the target is relatively close and background suppression is important.
Diffuse reflective models
With diffuse reflective models, light is emitted and the target is used to reflect light back to the sensor. The transmitter and receiver or housed together, eliminating the need for a separate receiver or reflector. Any reflective target can be detected and colours can also be differentiated.
Benefits of Fibre Optic Sensors
Fibre optic sensors are compact because the detection circuit is located in the amplifier, allowing for detection even in narrow spaces. Installation and adjustment are easy and the devices have high environmental resistance—just a few of the advantages offered by fibre optic sensors.
Fibre optic heads are compact and ideal for mounting in tight spaces. Additionally, the cables connecting the fibre optic heads are highly flexible, allowing for the cable to be easily routed. For example, mounting on a robotic arm is common for fibre optics.
Also, because the fibre units do not house any electrical circuits, they are resistant to temperature, humidity, vibration, impacts and fluids. This ensures high operation reliability even in locations where electrical noise is generated.
Most fibre optic sensors use light from an LED to detect targets, enabling detection of a wide variety of materials. This also allows for faster response times compared to other sensors.
A wide variety of target materials can be detected including metal, glass, plastic, wood and even liquid. Stable detection is also possible for low-reflectivity target materials such as rubber and sponges. This is achieved by increasing the amount of emitted light. Some models also include a switch for adjusting the light intensity to help solve light intensity saturation problems caused by too much light. Light is emitted from the fibre unit at high speeds, and the fibre optic sensor has no moving parts, significantly reducing both operation and response times.
There are several types of detection methods with fibre optic sensors, including thrubeam, reflective, retro-reflective and definite-reflective. Each method uses an LED or other light source for non-contact detection. This prevents damage to both the target and the sensor.
There are several types of detection methods with fibre optic sensors, including thrubeam, reflective, retro-reflective and definite-reflective. Each method uses an LED or other light source for non-contact detection. Non-contact measurement ensures targets are not damaged while also protecting the sensor.
Some fibre optic sensors are also capable of long-range detection by increasing the power of emitted light, while still having fast response times. This range of sensing options allow users to choose the right combination to best suit their specific needs.
Fibre Optic Sensor Case Studies
Target detection in high-temperature environments
In high-temperature environments such as drying rooms, sensors with detection circuits may be damaged as the detection circuit heats up. FU Series fibre units, however, do not have detection circuits in the sensing head. Heat-resistant fibre units can handle temperatures of up to about 300°C (572°F).
The high-output FS-N40, with its newly developed NEO Parabolic LED, offers 7.5 times the received light intensity of conventional models. Meanwhile, the TERA power mode offers 220 times more power with the flick of a switch. These features enable long-range detection with no influence from heat.
Product drop detection
When using a sensor to detect the number of dropped steel balls (or something similar) the position of the targets will not be consistent. Changes in light intensity due to dust or dirt can also result in false detections. Only sudden light intensity changes caused by a passing target should be detected.
The FU-E40 Fibre Unit (FU Series) uses an area light to detect targets passing in various positions. The amplifier makes it possible to ignore gradual changes in light intensity caused by dust or dirt, ensuring that only sudden light intensity changes caused by a passing target are detected. Also, because the light is focused, this sensor can be used in crowded or tight spaces.
This site provides basic information to better understand sensors. Nine varieties of sensors are highlighted based on operating principle, structure, characteristics and variations. Learn all about sensors starting from the basics.
Frequently Asked Questions About Fibre Optic Sensors
Photoelectric sensors use light to detect the presence or absence of targets. Such sensors usually use an LED as the light source and consist of two parts: a light transmitter and a light receiver. As the target passes between the transmitter and the receiver, the reflected or blocked light is converted into an electrical signal and output.
Although fibre optic sensors detect targets in basically the same way, the amplifier and the head are connected by a fibre unit. Because the amplifier that outputs the light and the transmitter and receiver are separated, these devices can be combined in various ways, so detection can be performed in various environments. The fibre unit is also incredibly thin and compact, so installation is possible in a wider variety of locations.
Detection errors are more likely when detecting small targets. Slower response speeds may also prevent detection of small, dropped targets.
To prevent such errors, select a thrubeam sensor with a small optical axis or use a slit to reduce the optical axis when detecting small targets. Doing so will stabilise detection while still providing an area large enough to capture the target.
The FU-E40 Fibre Unit (FU Series) uses an area light to detect targets passing in various positions. The amplifier makes it possible to ignore gradual changes in light intensity caused by dust or dirt, ensuring that only sudden light intensity changes caused by a passing target are detected. Also, because the light is focused, this sensor can be used in crowded or tight spaces.
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