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Fiber-optics has gained immense popularity because of its extreme lightness, low attenuation, narrow diameter, and transmission security. The devices also have the ability to send data over long distances.
The fiber-optic revolution has transformed fiber-optic sensors as well. A fiber-optic sensor is a device that emits and receives light energy and converts it to electric current. The cable transmits the light to areas that would be otherwise inaccessible.
Also called optical fiber sensors, the devices contain a sensing element with a fiber optic cable. They are used in diverse applications, including temperature, pressure, vibrations, displacements, rotations, and chemical detection.
Advantages of Fiber-Optic Sensors
The principal reason for their popularity is that they are not dependent on electrical power and can, therefore, be put into use at remote locations, assisted by their small size.
With the main component being an optical fiber, it has no moving parts to break down, nor does it have electrical circuits. This makes it resistant to all electrical and radiofrequency interference. Thus, it can be kept apart from all known sources of electricity, allowing for accurate sensing.
Fiber-optic sensors are also suitable for use in the most dangerous of environments, including oil refineries, grain storage bins, mines, pharmaceutical manufacturing units, and chemical production plants, because they emit no sparks. This also makes it safe to repair the broken cables.
Other advantages include:
- No need for contact
- Easy to install in most cases
- Solid-state systems with high reliability
- Easy to interface with data communication systems
- Secure transmission of data
- Allows distributed sensing
Newer designs are emerging with even more benefits:
- Remote fiber-optic sensors have come out with digital LEDs for easy readouts. This makes the configuration and monitoring of user applications very easy. It also permits rapid diagnosis of misalignment, as well as of early cable tip degradation, which leads to deterioration of performance.
- Newer fiber-optic sensors need much less wiring than before, often requiring only output wiring for the slave sensors.
- Dual-output sensors are also being offered, combining two sensors in the same package, such as two digital or one digital with one analog output.
- Lockout security features are also emerging to prevent tampering or unnecessary adjustment of settings.
- In most cases, a CPU is integrated into the sensor with an A/D converter to increase the resolution and response time.
- Many sensors also walk the users through the setup.
- In dangerous environments, a remote setting is possible. For instance, using a remote-control programmer with a cable to set up and monitor the cable from a safe location.
- Digital readouts are available to help refine the threshold point and to show the incident level.
- The configuration copy-paste function often allows instantaneous to set up of additional sensors or a group of sensors on a second device, once one sensor has been successfully installed.
Physical sensors analyze physical properties such as pressure, strain, stress, flow, temperature, and fatigue.
Biomedical sensors analyze various biomedical quantities in the form of derived electrical signals and are useful in all types of biomedical healthcare analyzers.
Chemical sensors use fiber-optic technology to detect chemicals at various concentrations.
Thus fiber-optic sensors may be used as:
- Low-cost sensors for all kinds of applications
- Distributed sensors in smart structures and the oil and gas industry
- Smart fabrics for aircraft, medical, and geotechnical devices and structures
- Sensors for food and water quality assurance
- Environmental monitors for gas & emissions sensing, and detection/monitoring of pollutants
Monitoring the Structural Health of Mechanical Components
Fiber-optic sensors are used today to evaluate the mechanical properties of various materials because of their small size and weight, simple installation, and lack of sensitivity to interference by electromagnetic radiation.
The cost savings are significant, and distributed sensing allows a much broader coverage and therefore more assurance that damage will be detected early.
Distributed fiber-optic sensing is also very useful for mechanical analysis of welds, composite materials, fatigue testing, leaf springs, and many other situations.
Monitoring the Structural Integrity of Moving Machines Such as Wind Turbines
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Their compact and lightweight profile recommends the use of fiberoptic sensors in this situation, especially combined with their lack of electromagnetic interference from lightning, multiplexing capability, low cost, and distributed sensing.
They allow accurate evaluation of strain data and temperatures over the whole structure, for timely damage detection.
This removes the need for repeated inspections and needless part replacements on a time-bound schedule while minimizing the risk of large-scale failure of the structure.
Monitoring Power Generators
Aging electricity generators are very susceptible to mechanical failure which may reduce the power output.
Overheating is another consequence which may be the result of overloading the machines or due to ventilation problems, for instance.
Distributed fiber-optic sensing allows multiplexing of sensors with just one optical fiber, for real-time monitoring at a cost-effective rate.
Sources and Further Reading