PI's Fiber Optic Systems are based on proven technology used by the U.S. Navy to monitor the environment surrounding its ships and submarines. Every PI system consists of two key integrated building blocks, a fiber optic sensor that detects the measured events by observing changes to a reflected light signal, and an accompanying remote electronics module (called an interrogator) that converts the optical signals into digital electronic data. For some applications, an acoustic processor may be added to provide sophisticated signal processing techniques to the digital output for beamforming, signal classification, 3-D imaging, etc.
The fiber optic sensing cable is a high sensitivity, fiber optic assembly enabling the detection of very low sound, vibration, or strain levels. The fiber optic sensing cables designed by PI employ Fiber Bragg Gratings (FBGs) embedded into the core of the fiber. (In “laymen’s terms” FBGs are partially-reflective filters permanently embedded into the core of the optical fiber by exposing it to a special high-intensity laser light.)
Typical Fiber Optic Cable With Embedded Fiber Bragg Gratings
PI packages this sensor fiber into rugged cables specifically designed for the various operating environments, be it downhole in an oil well, on the ocean bottom, attached to a fence or pipeline, or buried around the perimeter of a secure facility. The FBGs themselves then become unique, addressable sensors, or they can be used to divide the fiber into sections, called sensing zones. Spools of fiber with the FBGs are incorporated into rugged fiber optic cables. Once assembled into an appropriate cable based upon the application, the optical fiber is fully protected from damage. Because the optical fiber is the sensor, no electronics are required in the sensor cable. Every inch of the cable is acoustically sensitive ensuring that there are no gaps in coverage. A single cable can be up to 25 km long and include hundreds of discrete detection zones, each from tens to hundreds of meters long. When an application requires extremely long monitoring distances, multiple sub-systems can be linked together into a single system capable of covering hundreds, or more, miles.
Typical System Line Diagram
Another key advantage of the PI technology is that all the sensitive electronics are located in the CPU / Interrogator. The CPU / Interrogator is typically mounted in a standard electronics cabinet at the user interface end of the system, usually in a central monitoring station or other secure, weather-proof structure. The CPU / Interrogator is designed to provide a very high fidelity digital reproduction of the detected events with high linearity and dynamic range, with stable signal scaling and low distortion.