F-O Weighing Should Please Haulers

After a few false starts, weigh-in-motion technology is on the move again—to the certain delight of long-distance haulers who don't like idling in line at conventional weigh stations.

 Multisensor weigh-in-motion could do away with idling in lines.
Multisensor weigh-in-motion could do away with idling in lines.

I*Sense is a multisensor system based on fiber-optic Bragg gratings (FBGs). The developer, Intelligent Fiber Optic Systems (IFOS), is working on sensors that, embedded in highway pavement, will be able to instantly detect and relay to local or remote command centers a truck's gross weight and speed. An FBG sensing system is extremely sensitive to nearly any change in its enviroment—strain, temperature, pressure, displacement, or acceleration. The underlying principle of FBGs is that any extension or compression due to an external force changes the spacing of the grating, thus altering the center of the wavelength of the light reflected from the grating. This change in the reflectivity spectrum can be detected.

The hard part is getting multiple FBG sensors to function properly on a single strand of fiber. Each sensor must have its own wavelength segment so that the signals do not overlap. As an FBG sensor undergoes strain, signals shift in wavelength within their bandwidth range, so the complete system needs an optical source that continuously monitors the sensors. The resulting reflection spectra are analyzed by a photonic spectral analyzer and an interface module that records wavelength shifts. Accuracy in the light source and detection module is of the greatest importance, as is the specific wavelength-division multiplexing technique used. Maintaining such a degree of accuracy would suggest a low sampling rate, but IFOS has found a way to keep it high.

The technology could also be deployed in hard-to-reach places such as oil and gas pipelines, where it could measure corrosion levels and possible intrusions on miles of pipeline sections. Next up will be addressing the problem of sensing asphalt surfaces, which are more subject than concrete to frequent changes in strain, temperature, and pressure.

Contact Ky Good, Intelligent Fiber Optic Systems, Sunnyvale, CA; 408-328-8648, kg@ifos.com, www.ifos.com.