Fiber optic moisture sensor with moisture-absorbing reflective target

• US 4,634,856 A
• Filed: 08/03/1984
• Issued: 01/06/1987
• Est. Priority Date: 08/03/1984
• Status: Expired due to Fees

• Current Assignee: United States Department of Energy
• Original Assignee: United States Department of Energy
• Inventors: Kirkham, Randy R.
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US06/637,627
• Time in Patent Office: 886 Days
• Field of Search: 250/227, 250/577, 250/231 R, 73/293, 455/610, 455/612
• US Class Current: 250/227.25
• CPC Class Codes: G01N 21/431 Dip refractometers, e.g. using optical fibres
• CPC Class Codes: G01N 21/7703 using reagent-clad optical fibres or optical waveguides using measurement of total internal reflection or attenuated total reflection G01N21/552; optical fibres or waveguides per se G02B
• CPC Class Codes: G01N 21/81 Indicating humidity
• CPC Class Codes: G01N 21/8507 Probe photometers, i.e. with optical measuring part dipped into fluid sample

Abstract

A method and apparatus for sensing moisture changes by utilizing optical fiber technology. One embodiment uses a reflective target at the end of an optical fiber. The reflectance of the target varies with its moisture content and can be detected by a remote unit at the opposite end of the fiber. A second embodiment utilizes changes in light loss along the fiber length. This can be attributed to changes in reflectance of cladding material as a function of its moisture content. It can also be affected by holes or inserts interposed in the cladding material and/or fiber. Changing light levels can also be coupled from one fiber to another in an assembly of fibers as a function of varying moisture content in their overlapping lengths of cladding material.

Claims

1. A method for monitoring environmental moisture changes, comprising the following steps:

locating a optical fiber assembly within the environmental area being monitored;

transmitting light signals through the optical fiber assembly from a light source to and from a target whose reflectance is a function of the target'"'"'s moisture content;

measuring the returned light reflected by the target;

and detecting changes in the light signals transmitted through the optical fiber assembly from the light source as an indication of the moisture conditions to which the optical fiber assembly is subjected.

2. An apparatus for monitoring environmental moisture, comprising:

a optical fiber assembly located within the environmental area being monitored;

a light source for directing light signals through the optical fiber assembly;

a moisture-sensitive reflective target at an end of at least one optical fiber within the optical fiber assembly and exposed to said light source;

and detection means for measuring changes in the reflectance of said target as an indication of the environmental moisture conditions to which the target is subjected.