POF strain sensor using phase measurement techniques
View Patent ↗An optical fiber sensor has a measurement path and a reference path. Both paths each consist of two optical fibers and are fed with modulated light. The fibers of the reference path have a predefined difference in length, whereas the fibers of the measurement path are the same length. All fibers are at approximately the same temperature. An evaluation circuit determines the phase differences in each case between the fibers of the measurement path and of the reference path. A measurement value calculated from the phase differences is then output.
1. Optical fiber sensor for a temperature-compensated measurement of a deformation in a mechanical component, comprising:
a first measurement fiber which is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length and a second measurement fiber which either is attached loosely to the mechanical component or is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length;
a first optical transmitter fed by a signal generator to generate a modulation signal having a modulation frequency and generating an optical measurement signal coupled via a first Y-coupler into the first measurement fiber and into the second measurement fiber;
a first optical receiver for receiving an optical measurement signal passed through the first measurement fiber;
a second optical receiver for receiving an optical measurement signal passed through the second measurement fiber;
means for generating an optical reference signal coupled via a second Y-coupler into a first reference fiber and into a second reference fiber, wherein the first reference fiber and the second reference fiber have different lengths and output signals of the first reference fiber are supplied to the first optical receiver and those of the second reference fiber are supplied to the second optical receiver;
an optical changeover switch for switching the first optical transmitter to either the measurement fibers or the reference fibers; and
an evaluation unit which determines a first phase difference from the signals of the first optical receiver and of the second optical receiver while feeding-in measurement signals from the measurement fibers and also a second phase difference while feeding-in reference signals from the reference fibers and outputs a measurement value determined from the first phase difference and the second phase difference.
2. Optical fiber sensor according to claim 1 , wherein the measurement fibers and the reference fibers are thermally coupled to one another or are at approximately the same temperature.
3. Optical fiber sensor according to claim 1 , wherein the first measurement fiber and the second measurement fiber have approximately the same length.
4. Optical fiber sensor according to claim 1 , wherein the first reference fiber and the second reference fiber have a predefined difference in length.
5. Optical fiber sensor according to claim 1 , wherein the measurement fibers are connected to the mechanical component in such a way that during a deformation of the mechanical component the changes in length of the measurement fibers run in opposite directions.
6. Optical fiber sensor according to claim 1 , wherein the output signals of the first reference fiber are supplied to a separate first optical reference receiver and the output signals of the second reference fiber are supplied to a separate second optical reference receiver and the evaluation unit evaluates the corresponding signals of the reference receivers.
7. Optical fiber sensor according to claim 1 , wherein instead of the first optical transmitter and the first Y-coupler two optical transmitters are provided.
8. Optical fiber sensor according to claim 1 , wherein the optical reference signal is modulated with a modulation signal of a frequency different to a modulation frequency of the optical measurement signal.
9. Optical fiber sensor according to claim 1 , wherein a modulation signal of the optical reference signal and a modulation signal of the optical measurement signal has a sinusoidal or rectangular curve shape.
10. Optical fiber sensor according to claim 1 , wherein the optical reference signal or the optical measurement signal has a wavelength in the visible range.
11. Wind power plant comprising an optical fiber sensor according to claim 1 for measuring a deformation of at least one rotor blade.
12. Optical fiber sensor for a temperature-compensated measurement of a deformation in a mechanical component, comprising
a first measurement fiber which is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length and a second measurement fiber which either is loosely attached to the mechanical component or is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length;
a first optical transmitter fed by a signal generator to generate a modulation signal having a modulation frequency and generating an optical measurement signal coupled via a first Y-coupler into the first measurement fiber and into the second measurement fiber;
a first optical receiver for receiving optical measurement signals passed through the first measurement fiber;
a second optical receiver for receiving optical measurement signals passed through the second measurement fiber; and
a first reference fiber and a second reference fiber coupled to the first optical transmitter, wherein the first reference fiber and the second reference fiber have different lengths and the output signals of the first reference fiber are supplied to the first optical receiver and those of the second reference fiber are supplied to the second optical receiver;
an optical changeover switch for switching the first optical transmitter to either the measurement fibers or the reference fibers;
an evaluation unit which determines a first phase difference from the signals of the first optical receiver and of the second optical receiver while feeding-in measurement signals from the measurement fibers and also a second phase difference from signals supplied from the signal generator to the evaluation unit using two electrical lines, and outputs a measurement value determined from the first phase difference and the second phase difference.
13. Optical fiber sensor according to claim 12 , wherein the measurement fibers and the reference fibers are thermally coupled to one another or are at approximately the same temperature.
14. Optical fiber sensor according to claim 12 , wherein the first measurement fiber and the second measurement fiber have approximately the same length.
15. Optical fiber sensor according to claim 12 , wherein the first reference fiber and the second reference fiber have a predefined difference in length.
16. Optical fiber sensor according to claim 12 , wherein the measurement fibers are connected to the mechanical component in such a way that during a deformation of the mechanical component the changes in length of the measurement fibers run in opposite directions.
17. Optical fiber sensor according to claim 12 , wherein instead of the first optical transmitter and the first Y-coupler two optical transmitters are provided.
18. Optical fiber sensor according to claim 12 , wherein the modulation signal has a sinusoidal or rectangular curve shape.
19. Optical fiber sensor according to claim 12 , wherein the optical measurement signal has a wavelength in the visible range.
20. Wind power plant comprising an optical fiber sensor according to claim 12 for measuring a deformation of at least one rotor blade.
21. Optical fiber sensor according to claim 1 , wherein the measurement fibers and the reference fibers are thermally coupled to one another and are at approximately the same temperature.
22. Optical fiber sensor according to claim 1 , wherein the optical reference signal and the optical measurement signal has a wavelength in the visible range.
23. Optical fiber sensor according to claim 12 , wherein the measurement fibers and the reference fibers are thermally coupled to one another and are at approximately the same temperature.
24. Optical fiber sensor according to claim 12 , wherein the two electrical lines are of different lengths.
25. Optical fiber sensor according to claim 7 , wherein the two optical transmitters are fed with a same electrical signal from the signal generator.
26. Optical fiber sensor according to claim 17 , wherein the two optical transmitters are fed with a same electrical signal from the signal generator.
27. Optical fiber sensor for a temperature-compensated measurement of a deformation in a mechanical component, comprising:
a first measurement fiber which is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length and a second measurement fiber which either is attached loosely to the mechanical component or is connected at at least two points to the mechanical component and is changed together with the mechanical component at least partially in its length;
a first optical transmitter fed by a signal generator to generate a modulation signal having a modulation frequency and generating an optical measurement signal coupled via a first Y-coupler into the first measurement fiber and into the second measurement fiber;
a first optical receiver for receiving an optical measurement signal passed through the first measurement fiber;
a second optical receiver for receiving an optical measurement signal passed through the second measurement fiber;
means for generating an optical reference signal coupled via a second Y-coupler into a first reference fiber and into a second reference fiber, wherein the first reference fiber and the second reference fiber have different lengths and the output signals of the first reference fiber are supplied to the first optical receiver and those of the second reference fiber are supplied to a the second optical receiver;
an optical switch for switching the first optical transmitter to the reference fibers; and
an evaluation unit which determines a first phase difference from the signals of the first optical receiver and of the second optical receiver while feeding-in measurement signals from the measurement fibers and also a second phase difference while feeding-in reference signals from the reference fibers and outputs a measurement value determined from the first phase difference and the second phase difference.
28. Optical fiber sensor according to claim 27 , wherein the measurement fibers and the reference fibers are thermally coupled to one another or are at approximately the same temperature.
29. Optical fiber sensor according to claim 27 , wherein the first measurement fiber and the second measurement fiber have approximately the same length.
30. Optical fiber sensor according to claim 27 , wherein the first reference fiber and the second reference fiber have a predefined difference in length.
31. Optical fiber sensor according to claim 27 , wherein the measurement fibers are connected to the mechanical component in such a way that during a deformation of the mechanical component the changes in length of the measurement fibers run in opposite directions.
32. Optical fiber sensor according to claim 27 , wherein the output signals of the first reference fiber are supplied to a separate first optical reference receiver and the output signals of the second reference fiber are supplied to a separate second optical reference receiver and the evaluation unit evaluates the corresponding signals of the reference receivers.
33. Optical fiber sensor according to claim 27 , wherein instead of the first optical transmitter and the first Y-coupler two optical transmitters are provided.
34. Optical fiber sensor according to claim 27 , wherein the optical reference signal is modulated with a modulation signal of a frequency different to a modulation frequency of the optical measurement signal.
35. Optical fiber sensor according to claim 27 , wherein a modulation signal of the optical reference signal and a modulation signal of the optical measurement signal has a sinusoidal or rectangular curve shape.
36. Optical fiber sensor according to claim 27 , wherein the optical reference signal or the optical measurement signal has a wavelength in the visible range.
37. Wind power plant comprising an optical fiber sensor according to claim 27 for measuring a deformation of at least one rotor blade.