Fiber optical measuring device

• US 4,342,919 A
• Filed: 04/07/1980
• Issued: 08/03/1982
• Est. Priority Date: 04/10/1979
• Status: Expired due to Term

• Current Assignee: Asea Aktiebolag (ABB Limited)
• Original Assignee: Asea Aktiebolag (ABB Limited)
• Inventors: Brogardh, Torgny
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Hostetter, Darwin R.
• Application Number:
  US06/138,112
• Time in Patent Office: 848 Days
• Field of Search: 250/577, 250/227, 73/293
• US Class Current: 250/577
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01F 23/2922 with light-conducting sensing elements, e.g. prisms
• CPC Class Codes: G01N 21/431 Dip refractometers, e.g. using optical fibres
• CPC Class Codes: Y10S 250/904 with single light guide element to guide light in a continuous path

Abstract

The invention relates to a fiber optical measuring device for measuring physical parameters of a medium, preferably the level thereof, and it comprises an electronic unit and a transducer unit interconnected by an optical fiber, the transducer including at least one light guide connected to the optical fiber. The light guide is adapted to be lowered or introduced into the medium, the level, or other parameters, of which is to be measured, the light guide having a core with a higher refractive index than the surrounding sheath. The sheath has one or more regions along the light guide that are light transparent by being uncovered or only very thinly covered. When the guide is immersed into the medium, it influences the channel such that light in the thinly covered or uncovered regions of the guide is transmitted from the core, which light is representative of the level, or other parameter, of the medium.

Claims

1. A transducer for a fiber optical measuring device for the measurement of physical parameters of a medium, comprising:

at least one light guide for receiving light signals and transmitting output light signals representative of the parameter of said medium being measured and adapted to be partially immersed into said medium;

a sheath surrounding said light guide and including at least one transparent region thereof;

said light guide further including a core having a higher refractive index than said sheath;

said core transmitting light from said at least one transparent region at the immersed portion of said light guide to produce said output light signals; and

light transmission varying means spaced from said light guide and being brought into optical contact with said core by immersion of said light guide into said medium such that the light transmitted from said at least one transparent region is altered by said medium.

2. A transducer as in claim 1 wherein said medium is in optical contact with said core in said at least one transparent region immersed within said medium.

3. A transducer as in claim 1 wherein said light transmission varying means has a refractive index greater than or equal to the refractive index of said core.

4. A transducer as in claim 3 wherein said light transmission varying means is a resilient membrane adapted to be pressed against said core by immersion of said light guide into said medium at clearly defined portions of said core.

5. A transducer as in claim 1 wherein said light transmission varing means includes surface portions providing a plurality of well-defined contact points with said core upon immersion of said light guide in said medium.

6. A transducer as in claim 5 wherein said light transmission varying means is a wire coil wound around the core of said light guide.

7. A transducer as in claim 5 wherein said light transmission varying means is a corrugated light conductor surrounding the core of said light guide.

8. A transducer as in claim 1 wherein said light transmission varying means includes a surface curving along the longitudinal axis of the light guide, said light guide being partially bent along said curved surface by said medium upon immersion of said light guide therein.

9. A transducer as in claim 1 wherein said light guide is an optical fiber.

10. A transducer as in claim 9 wherein said optical fiber is wound in the form of a helical coil.

11. A transducer as in claim 1 wherein said light transmission varying means is spaced from said core, and the space between said core and said light transmission varying means includes a liquid having a well-defined refractive index.

12. A transducer as in claim 1 further comprising an interference filter at the end of said at least one light guide receiving light signals.

13. A fiber optical measuring device using the transducer as in claim 1 and further comprising:

means for generating light signals having first and second different wavelengths;

optical fiber means for transmitting said generated light to said at least one light guide;

interference filter means for reflecting at least a portion of said light signals at the end of said at least one light guide;

said optical fiber means including an optical fiber for transmitting said output light signals;

means for detecting said output light signals from said fiber optical means; and

means for processing the detected signals to generate a signal representative of the physical parameter of said medium.

14. The fiber optical measuring device as in claim 13 further comprising means for alternately periodically generating light signals of said first and second wavelengths.

15. A fiber optical measuring device as in claim 14 further including means for temperature stabilizing said means for generating light signals.

16. A fiber optical measuring device as in claim 14 wherein said means for processing includes first and second sample and hold circuits each having an input controlled in synchronization with the operation of said means for periodically and alternately generating said light signals to alternately input the output of said light detecting means, and means for dividing the respective outputs of said first and second sample and hold circuits for generating a signal representing the measured physical parameters of the medium.