Fiber Optic Sensing and Cabling Technologies

Fiber optic sensors work well in tight spots and applications with a high degree of electrical noise, but care must be taken when specifying these critical components.

Sensing part presence in machines, in fixtures, and on conveyors is an important component of industrial automation. Error-proofing assembly and controlling sequence based on the presence or absence of a part is often required. Many types of sensors are available, including inductive, magnetic, capacitive, and photoelectric. Each has its own strengths and weaknesses depending on the application.

Photoelectric sensors come with a variety of light-emission types (infrared, visible red, laser Class 1 and 2), sensing technologies (diffuse, background suppression, reflective, through-beam), and housing configurations (photo-eye or fiber optic). Fiber cabling is immune to electrical noise, and the electronics can be mounted away from the noise in a shielded enclosure.

Another very common application is small part assembly. These operations tend to be fully automated, and thus require multiple sensors to confirm part placement (seated) and assembly verification to confirm completion of an operation. Typically, the parts are moving in and out of a stage quickly on carriers or an indexing table. Because travel tolerance is minimal, precise measurement of position becomes essential.

A common issue in fiber optic installations concerns excessive flexing of the fibers. Since the fiber cables are bundles of individual fibers, they typically feel quite pliable, allowing an installer to easily bend the fibers beyond their recommended maximum bend radius. This can cause irrecoverable plastic deformation of the fibers, which will reduce the light transmission or, in the worst case, sever it entirely. The maximum bend radius, listed with all fibers, varies depending on fiber material, bundle size, and fiber dispersion in the bundle—and it must be adhered to in all cases.

Regardless of the application, machine builders must select the proper sensor technology. If fiber-optic sensors are used, amplifiers and fiber-optic heads must be carefully selected for the application to provide robust sensing performance.

Fiber Optic Sensors for Borehole seismic technology system

Seismic techniques are the main techniques for the characterization of subsurface structures and stratigraphy. Borehole technology system provides the highest resolution characterization and most precise monitoring results because it generates a higher signal to noise ratio and higher frequency data than surface seismic techniques. A new generation of fiber optic borehole sensor systems has been developed based on all fiber optic data transmission and fiber optic sensor technologies. The new fiber sensors are much more sensitive and are able to record much larger bandwidth data with better vector fidelity than is possible with current seismic sensor technologies. The new sensors also can operate in most hostile environments found in boreholes such as pressure and temperature conditions. This improvement in data quality and density will generate better images and more precise monitoring results, which will allow a much improved high-resolution interpretation and ultimately better oil and gas production.

Since the borehole seismic system does not require electric power for either the optical sensors or the hydraulically operated deployment system, the entire system is intrinsically safe. The fiber-optic seismic sensor system measures the strain of the fiber between two Fiber Bragg gratings surrounding the mandrel using an interferometric measurement technique comparing the phase angle between two spaced reflections from the same light pulse traveling in the fiber. It is using a time-division multiplexing technique to transmit the dynamic fiber strain information to the interrogators. This allows the measurement of extremely small strains in the fiber. The fiber optic seismic sensor is self-standing to electric and electromagnetic interference in the borehole since the system does not require any electronics at the fiber optic sensor end. This design also makes the fiber optic seismic sensor extremely robust and able to operate in extreme environments such as temperatures up to 300 C.  All the sensors are calibrated so the optical output amplitude into absolute acceleration can be mapped. The sensors have also proved to be about 100 times more sensitive than the regular coil geophones that are used in borehole seismic systems today.

Optromix Company manufactures a wide range of sensors, that are able to feel the slightest deformation of the structures.

Medical fiber optic sensing products and technologies

The range of medical devices incorporating optical fibers has taken a slow technological growth, with the bulk of the industry focused on endoscopy and various methods of optical power delivery for cutting, dissecting, and ablating. These technologies utilize an optical fiber’s mechanism—the ability to guide light from one location to another.

Fiber sensing technologies offer significantly advanced functionality by utilizing their inherent sensitivity to temperature, strain, and pressure. During the last five years, the medical industry has taken significant steps to adapt historic fiber-optic sensing methods to enable them to be used within in vivo environments.

The main area for recent technological developments driving fiber sensors into the medical industry has focused on minimally invasive surgery (MIS). The benefits of MIS are now well-founded, encouraging surgical-tool manufacturers to invest their money in new technology developments to pioneer new MIS procedures or to further improve existing procedures. Three exciting recently developed fiber optic sensing technologies for MIS are focused on here: haptic feedback, 3D shape sensing, and pressure sensing.

By utilizing multiple FBGs or manipulating the FBG structure, it is possible to obtain a spatially distributed strain profile. Such FBGs can be applied along the length of a surgical tool to enable haptic feedback at the regions of most concern. A prime example of this is to add haptic sensing to a grasping tool, where both the grasping and spreading forces can be measured and fed back to the surgeon to indicate how tightly they are grasping or how much force they are applying to pry tissues apart.

Fiber optic 3D shape sensing has been developed by several commercial groups to enable a dramatic reduction in the need for prolonged exposure to the visualization methods, as the optical fiber can track itself in three dimensions and thus if laid within a catheter, can recreate the shape of the catheter. This technique relies on a mixture of FBG and fiber technology, where a very special fiber has been developed specifically for this application. Optical fibers also can be optimized to be sensitive to the hydrostatic pressures experienced within the body. These new applications are being opened up by a mixture of economic desire and technology development. Specialty optical-fiber manufacturers continue to pioneer new fiber designs that medical-device manufacturers can exploit. This enables a greater diversification of medical-device product ranges and opens up new procedures that were not previously possible with minimally invasive surgery.

 

Pipeline Integrity, Safety, Structural health Monitoring and leak detection with the Fiber Optic Sensor system

Distributed fiber optic sensing is tested through practice technology for online monitoring of temperature, strain, vibration, and sound over long distances with the high local resolution that is apt to improve pipeline integrity, pipeline safety, and security considerations. Fiber optics distributed temperature sensing techniques have found applications in various domains such as civil engineering, oil, and gas, power plants, fire detection, etc.

Pipelines are the most modern, effective, and reliable global transport systems for oil, gas, and water. In order to guarantee the smooth transport of products the pipeline systems must be regularly maintained and monitoring. Optical sensing systems today facilitate pipeline monitoring and integrity as preventive means to continuously protect or monitor pipelines. The systems are based on interferometric sensing where ultra-stable, low noise lasers interrogate an optical fiber acting as one long continuous sensor embedded or attached to the pipeline. The monitoring of temperature profiles over long distances by means of optical fibers represents a highly efficient way to fiber optic leak detection along pipelines, in dams, dikes, or tanks. Different techniques have been developed taking advantage of the fiber geometry and of optical time-domain analysis for the localization of the information.

Distributed temperature sensing is used in all cases to improve the performance of computational monitoring systems. Although distributed temperature sensing is a well-proven technology that has shown to be able to detect very small leaks in a short time, it is very hard to calculate the minimum detectable leak size or to guarantee a maximum detection time which in many cases are necessary to receive pipeline operation licenses. Leak rates as low as 50 ml/min have been detected on a brine pipeline by temperature monitoring and identification of local temperature anomalies.

GeoHazards like earthquakes, landslides, and surface subsidence result in ground movement and thus put additional stress on the pipelines, tunnels, and other underground infrastructures. Structural health monitoring is a promising and challenging field of research in the 21st century. Civil structures are the most precious economic assets of any country, proper monitoring of these are necessary to prevent any hazardous situation and ensuring safety. Fiber Bragg Grating (FBG) sensors have emerged as a reliable, in situ, nondestructive device for monitoring, diagnostics, and control in civil structures. FBG sensors offer several key advantages over other technologies in the structural sensing field.

The transformer is the key equipment in a power system, to ensure its safe and stable operation is important. Transformers either raise a voltage to decrease losses or decreases the voltage to a safe level. The failures of transformers in service are broadly due to temperature rise, low oil levels, overload, poor quality of LT cables, and improper installation and maintenance. Out of these factors temperature rise, low oil levels and overload, need continuous monitoring to save transformer life. A DTS system increases the reliability of the distribution network, by monitoring critical information such as oil temperature, and the oil level of the transformer. Data are collected continuously. Monitoring the transformers for problems before they occur can prevent faults that are costly to fix and result in a loss of service life. With modern technology, it is possible to monitor a large number of parameters of a transformer monitoring system at a relatively high cost. At the present day, the challenge is to balance the functions of the monitoring system and its cost and reliability. 

Fiber Optic Sensor Solutions: today’s field experience of sensing system

Fiber optic sensor solutions have created new opportunities in general industry applications. The fiber optic sensors (temperature, pressure, deformation, and displacement) are designed to deliver precise measurements in harsh environments and in the case of electromagnetic interference, magnetic resonance imaging, radiofrequency, microwave, and high voltage applications.

The greatest advantages of the fiber optic sensors are its inert material. It is also an optimum transducer for use in harsh environments, like in geotechnical applications.

Fiber optic sensors more and more are attracting attraction in the aerospace and defense due to resistance to chemical corrosion, high pressure, high voltage, and lighting environments. Its lightweight and small size permit weight reduction on different monitoring areas and the capacity of long-range operation still conserving high sensitivity and large bandwidth ensuring a long term reliable monitoring.

Chemistry and food are both often related to microwave radiation. Gallium Arsenide (GaAs) semiconductor crystal is non-conductive, offers high temperature operating capability, they are suitable for microwave heated installations chemical digestion under pressure and temperature conditions. A fiber optic sensor can also be used in the food industry where microwaves are used in new product development to identify precise safe and effective cooking temperatures and time.

The inherent benefits of fiber optic point sensing technology for structural health monitoring applications. In addition, they are not affected by the external environment, large temperature variation, transversal strain, or lightning.

The renewable energy market is developing quite rapidly over the last years. With wind farms or hydrokinetic systems, there is a big need for low maintenance monitoring systems that are reliable and stable for a long period. With the property of being immune to EMI and insensitive to lightning strikes, it makes it a great fit for the growing renewable energy market.

The fiber optic sensing system is the ideal solution for monitoring well pressure and temperature in thermal recovery applications like steam-assisted gravity drainage (SAGD) or cyclic steam stimulation (CSS). The FBG sensors can be used in coiled or production tubing in production and injection wells giving accurate properly measurements for reservoir surveillance, process optimization, or pump control.

In-situ and continuous monitoring of the pressure in the producing for the better understanding of the reservoir condition FBG sensors rapidly detect steam breakthrough and efficiently diagnose changes in the reservoir.  Optimization of the production process forces the oil recovery rate and reduces the operating costs associated with steam injection and oil recovery.  A fiber optic sensing solution is offered in both single and multiple-point configurations. Hence, it gives the operators a large choice of real-time monitoring from monitoring well pumps to profiling a producing well. The application “downhole pressure and temperature measurement solution” is only one example of what is possible with fiber optic technology. The fiber optic measurement solutions are custom made according to the requirements.

Apodized Fiber Bragg Gratings (FBG)

Apodized FBGsFiber Bragg Gratings is one of the most meaningful developments in the areas of optical fiber technology, due to their flexibility and unique filtering performance. FBG is defined as the key component in dense wavelength division multiplexing on the basis of their low insertion loss, high wavelength selectivity, low polarization dependent loss, and low polarization modal dispersion.

When light propagates through the FBG in the narrow range of wavelength, the total internal reflection appears at Bragg wavelength and other wavelengths don`t have influence by the Bragg grating except some side lobes existing in the reflection spectrum. These side lobes are sometimes interfering, e.g. in some applications of fiber Bragg gratings as optical filters. They can be largely brought out with the technique of apodized FBG: the strength of the index modulation is smoothly ramped up and down along the grating.

 

The term apodization is concerned with the grading of the refractive index to approach zero at the end of the grating. Apodized gratings introduce the essential improvement in side-lobe suppression while maintaining reflectivity and narrow bandwidth. Gaussian and raised cosine methods are typically used to apodize an FBG. Each method has some special features and different methods of fabrication. The fabrication of apodized Gaussian Bragg gratings is using the two UV-pulse interfere with variable time delay, which strongly reduces the reflectivity at sidelobes and this method makes it possible to write off truly apodized gratings by the single exposure of a uniform phase mask.

The fabrication of Apodized Fiber Bragg Gratings has raised much interest because of its reduced reflectivity at sidelobes. It, therefore, increases the quality of optical filters and improves the dispersion compensation by simultaneously reducing the group delay ripples. Apodized FBG can be used to optimize the parameters of the introduced optical switch and may also prove to be useful as the optical sensing element in a range of other fiber sensor configurations, especially for grating-based chemical sensors, pressure sensors, and accelerometers.

Photonic Sensors: Technology and Applications for Safety Monitoring

Nowadays, photonics is an important part of the innovation-driven growth in an increasing number of fields. The application of photonics is distributed across several sectors: from optical data communications to imaging, lighting, and displays; from the manufacturing sector to life sciences, health care, security, and safety.

Photonic sensors have been designed for use in laboratories and industrial environments in order to detect a wide range of physical, biological, and chemical parameters. Photonics sensors can be defined as the set of techniques and scientific knowledge concerning the generation, propagation, control, amplification, detection, storage, and processing of the optical spectrum signals. In recent years, photonic sensors have been recognized as the technology that improves, extends across, and strengthens a wide variety of industrial sectors: healthcare, security, manufacturing, telecommunications, environment, aerospace, and biotechnology.

The photonic sensors market is classified generally by types and photonics applications. Type wise consist of fiber optic sensors, laser-based sensors, and biophotonic sensors. Application-wise, it is divided into construction, energy industry, oil and gas, military and aerospace, medical and industrial application. The photonic sensors market is diversified and fragmented. Photonic technology also has found a use for the industry, surgeries, and ordinary life besides its use in research laboratories.

The photonic sensors market is slowly moving from making general objectives to complicated tasks such as aircraft manufacturing applications that prescribed maximum precision. The usage of photonic sensing technology is increased in early detection and early-warning systems for biological hazards, structural flaws, and security threats. Sensors play a major role in the near future and, especially, in different photonic applications in the generation, distribution, and conservation of energy, as well as in the mitigation of the effects of energy production and consumption on the environment.

The photonic industry now is centering on the development of eco-efficient products that are projected to be developed and launched over the next few years. The need for enhanced safety and security solutions, better alternatives for conventional technology, and a rise in wireless sensing technology are some of the major factors that act as drivers for the photonic sensor market.

Optical fiber sensor technology and energy engineering

The power industry is one of the major markets for optical fiber sensor technologies. Most of the research and developments are currently done specifically for this sector. Fiber optic sensors have key advantages for this industry: they can monitor very lengthy facilities and it is completely resistant to electromagnetic waves.

Various new optical fiber sensor technologies are being developed right now. The hydro filter system, distributed thermal monitoring system, the current sensor (alternating and direct current), and high-frequency accelerometer are among them. Hydro filter system performs filtering processes that take place in a multileveled foundation of the facility. The real-time data obtained with the fiber optic filter, the data is analyzed and compared with the calculations done when the facility was designed. The fiber optic filter system is universal and may be used for industrial and civil engineering. Fiber optic filter controls the processes of temperature shift in closed and opened locations with limited access and in remote destinations. Moreover, fiber optic filter allows controlling several objects that have different sophistication levels with only one sensing element.

The hydro-technical cable contains the core of the modular construction with the central power element made of the dielectric rod. Optic modules are tied around the rod and an isolated copper electrical conductor is wrapped around them to ensure the constant temperature level inside the construction. This kind of fiber optic equipment allows increasing the sensitivity of the construction. Water blocking materials used inside the cable make it waterproof. Steep armor protects the fiber optic equipment from hundreds of kilos of steady-state pressure.

Monitoring boosters are also possible with the sensors of temperature and vibration. The temperature sensor is located in the liquid refrigerating agent at the top of the booster; this sensor may also serve as an alarm for when the liquid agent reaches the critical level.

There are many more different applications of optic fiber sensor technologies in the power industry. In Optromix Company we offer the highest quality product and we will deliver the fiber optic equipment according to your specific needs.

FBG monitoring systems for hydraulic structures

Any sophisticated construction requires constant tracking of its technical condition to detect inconsistencies between the projected calculations and the actual working parameters and to evaluate its compliance to the established standard. Currently, the most used sensors to monitor hydraulic structures are stringer transducers that perform very well under various climate conditions, especially in the areas of deep-frozen soil. However, the increasing sophistication of modern constructions is more demanding in terms of monitoring standards. Often it is no longer sufficient to use regular sensors. Hence, a new type of monitoring with fiber optic devices was created.

The length of these constructions and its complex structure demand special fiber optic devices monitor its safety. One of the most complicated constructions to place the fiber optic solutions is a hydro-electric power station. FBG sensors can be placed in the structures where regular stringer transducers fail, for example, in long shafts and tunnels. On top of that, fiber optic solutions are completely fire-safe, resistant to electromagnetic fields and radiation, and other interferences.

Tunnels in hydro-electric power stations can be equipped with the following fiber optic devices: FBG sensors for deformation, temperature, displacement, and pressure sensors. The deformation sensor is measuring the condition of the steel reinforcing, and it embedded on its surface. The sensor is covered with the isolating material to avoid the impact of the concrete. An additional temperature sensor is installed in the same location to track temperature changes that affect deformation. A displacement sensor is used to measure the joint opening between steel compression and a ram. The pressure sensor is used to measure the water pressure in the tunnel.

Optromix offers a variety of fiber optic solutions, and we will write a tailored FBG based on your specific needs.

Monitoring system for bridges

Fiber optics products can be used to monitor the condition of different bridges; it evaluates in real-time depreciation during the exploitation, provides public safety, and cuts the expenses for maintenance.

Data collected by these fiber optics products allow decreasing regular maintenance expenses of the constructions. All the information is stored in an orderly manner to enable sorting through long and short-term tracking periods. Using a monitoring system helps to use the facility in a more efficient way. Monitoring fiber optics products help to build the construction and to optimize the load in different situations, and it will make the utilization time.

The following parameters are measured with fiber optic product:

  • Relative linear beam deformation
  • Temperature next to the deformation place
  • The inclination of the supporting structure
  • Other physical dimensions

Beam sensors are located on the right and left sides of the bridge and the fiber optic product controls the pressure on the entire length of the construction, bridge conditions during the peak load and at relaxation time, relative changes in different structure elements during the exploitation period, climate changes effect.

Fiber optic product for inclination tracking controls the potential shift of the bridge over time. And the fiber optic product located at the central part of the bridge tracks the vibration and the danger of resonating frequencies.

The amount of sensors per bridge is always determined case by case. In general, it depends on the central part between the supporting structures. The part that takes the heaviest load is the central part of the bridge and it has to be measured precisely.

These sensors help to find weak parts of the structure and prevent damages and catastrophes.