The present invention is generally related to fiber optic array signal processors, and more particularly to an improvement over linear array signal processor systems that interrogate Fabry-Perot sensors.
The linear array signal processor (LASP) system interrogates Fabry-Perot sensors that have gaps ranging from 5 to 25 μm, a white light tungsten lamp with spectral intensity as shown in
The LASP system can be multiplexed with many channels sharing a single microprocessor, however, each channel must be interrogated in time by switching each channel on and off. With the existing system, any changes that occur to the environmental parameter associated with any channel while another channel is being interrogated is lost. When many channels are multiplexed in time with the existing system, the update rate per channel is slow. The present invention provides for a system that is able to process many channels simultaneously and overcomes the limitations of the existing system.
Objects and advantages together with the operation of the invention may be better understood by reference to the following detailed description taken in connection with the following illustrations, wherein:
While the present invention is described with reference to the preferred embodiment, it should be clear that the present invention should not be limited to this embodiment. Therefore, the description of the preferred embodiment herein is illustrative of the present invention and should not limit the scope of the invention as claimed.
Reference will now be made in detail to the preferred embodiment of the invention as illustrated in the accompanying drawings. The present invention discloses a method for multiplexing many fiber optic channels into one LASP signal conditioner.
Within the signal processor, the modulated light from the sensor exits the fiber as a cone shaped beam and is redirected from the mirror as a line with a Gaussian distribution. When the light passes through the Fizeau wedge cross correlator, a correlation burst as shown in
In order to determine the peak intensity given the characteristic Gaussian distribution, normalizing the readings based on the distribution resulting in a signal that looks like the signal shown in
As seen in
During calibration of the signal conditioner, the determination of the precise thickness of the wedge at each pixel along the CCD array is required. During the calibration of the sensor, calibration constants are entered into a file that are used to convert the gap into the appropriate engineering units, i.e., pressure or temperature. A calibration plot of sensor gap versus CCD pixel number is shown in
The method uses a two-dimensional (2-D) CCD array, e.g. 25 mm square, rather than the one-dimensional array used in the standard LASP described above. The 2-D array provides the capability to multiplex a large number of sensor signals from many fiber optic channels as shown in
A cylindrical lens could be substituted for the cylindrical mirror defined above (see
The polished fiber ends may be arranged in a variety of ways and held in a mounting block. In the preferred embodiment, sixty-four fibers are arranged side by side in two parallel V-blocks that are tilted at a slight angle as shown in
A Fizeau wedge, e.g. 25 mm square, changes thickness in one dimension only and covers the CCD array as observed in the top view of
There is also a wavelength shift caused by chromatic dispersion through the wedge. It is necessary to correct for the chromatic dispersion in the signal processing algorithm.
The two-dimensional CCD array of the present invention permits multiplexing of a large number of sensor signals. This approach enables a significant increase in the update rate per channel compared to the standard LASP.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/637,959, filed Dec. 21, 2004.
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