Optical Sensor For Extreme Environments

Abstract

An optical sensing probe includes a tube having a tip portion configured for placement in an environment in which conditions are to be sensed and an etalon having a known characteristic disposed proximate the tip portion. The tube also includes a head portion remote from the tip portion containing a light directing element for directing light beams at the etalon and receiving reflected light beams from the etalon wherein the received reflected light beams are used for determining an environmental condition proximate the tip portion. A method for measuring a thickness of the etalon may include directing a light beams at different frequencies at the etalon and receiving the light beams from the etalon. The method may also include identifying conditions of the respective light beams condition received from the etalon and then calculating a first thickness of the etalon responsive to the respective conditions and the known characteristic.

Description

SPECIFIC DATA RELATED TO INVENTION[0001]This application claims the benefit of U.S. provisional application No. 60 / 742,813 filed on Dec. 6, 2005.BACKGROUND OF INVENTION[0002]The present invention relates to optical sensors and, more particularly, to optical sensors using etalons for remote sensing in extreme environments.[0003]There are numerous vital sensing scenarios in commercial and defense sectors where the environment is extremely hazardous. Specifically, the hazards can be for instance due to extreme temperatures, extreme pressures, highly corrosive chemical content (liquids, gases, particulates), nuclear radiation, biological agents, and high Gravitational (G) forces. Realizing a sensor for such hazardous environments remains to be a tremendous engineering challenge. One specific application is fossil fuel fired power plants where temperatures in combustors and turbines typically have temperatures and pressures exceeding 1000° C. and 50 Atmospheres (atm). Future clean design...

AI Technical Summary

Benefits of technology

[0009]Ideally, one would like a robust optical sensor that can be remoted, is minimally invasive, works at high temperatures (e.g., 2000° C.) and pressures including chemically corrosive environments, requires low cost low loss optics, has high sensing resolution over any extended wide unambiguous range, and provides easy access to many sensing points. In commonly assigned U.S. patent application Ser. No. 11/185,540 incorporated herein by reference, modules for the needed extreme environment minimally invasive optical free-space laser beam targeted optical sensor using preferably single crystal Silicon Carb...

Problems solved by technology

Realizing a sensor for such hazardous environments remains to be a tremendous engineering challenge.

In addition, coal and gas fired power systems produce chemically hazardous environments with chemical constituents and mixtures containing for example carbon monoxide, carbon dioxide, nitrogen, oxygen, sulphur, sodium, and sulphuric acid.

Over the years, engineers have worked very hard in developing electrical high temperature sensors (e.g., thermo-couples using platinum and rodium), but these have shown limited life-times due to the wear and tear and corrosion suffered in power plants [R. E. Bentley, “Thermocouple materials and their properties,” Chap.

The single crystal Sapphire fiber FBG has a very large diameter (e.g., 150 microns) that introduces multi-mode light propagation noise that limits sensor performance.

Hence this described sensor frontend sensing element not only has low optical efficiency and high noise generation issues due to its multi-mode versus SMF design, the sensor frontend is limited by the lowest high temperature performance of a given component in the assembly and not just by the Sapphire crystal and zirconia high temperature ability.

In particular, the Sapphire Crystal is highly birefringent and hence polarization direction and optical alignment issues become critical.

Hence this temperature sensor design is again limited by the spectral spoiling plus other key effects when using very broadband light with MMFs.

Specifically, light exiting a MMF with the collimation lens has poor collimation as it travels a free-space path to strike the sensing crystal.

This all leads to additional coupling problems for the receive light to be picked up by the six MMFs engaged with the single fixed collimation lens.

Another problem plaguing this design is that any unwanted mechanical motion of any of the mechanics and optics along the relatively long (e.g., 1 m) freespace optical processing path from seven fiber-port to Sapphire crystal cannot be countered as all optics are fixed during operations.

Hence, this probe can suffer catastrophic light targeting and receive coupling failure causing in-operation of the sensor.

Although this design used two sets of manual adjustment mechanical screws each for 6...

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