Thermal measuring and testing – Temperature measurement – Temperature distribution or profile
Reexamination Certificate
2000-11-10
2003-04-15
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
Temperature distribution or profile
C374S143000, C250S227140, C385S012000
Reexamination Certificate
active
06547435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for monitoring temperature distributions and/or temperature anomalies on the basis of distributed fiber-optic temperature sensing as well as to novel applications of such methods.
2. Description of the Related Art
Distributed fiber-optic measurement principles use the integration of laser light impulses into an optical waveguide and the scattering effects thereof. The scattering of the laser light impulse takes place on the molecules of the optical waveguide. A small part of the laser light is thereby scattered back. The intensity and the spectral composition of the scattered light is accordingly determined by the molecules in the optical waveguide and by the behavior of the molecules.
The backscattered light is composed of different spectral portions, which are caused by different mechanisms of the interaction between laser light and the optical waveguide components and which thereby also include different information on the physical state of the optical waveguide. Thus, however, the optical waveguide itself turns into a sensitive element.
The Rayleigh backscatter component, which has the same wavelength as the integrated primary laser impulse, provides the highest peak in the scattered light spectrum and thereby essentially determines the exponential drop of the intensity time curve of the backscattered light. As inhomogeneities in the optical waveguide, local attenuation changes, micro ruptures, splice connections and the like cause the intensity in the Rayleigh backscatter component to change, said component of the scattered light spectrum is used for controlling the quality of optical waveguides or for error detection, respectively.
The interaction of the laser light with optical phonons in the optical waveguide, i.e. the scattering of the phonons on thermal grid vibrations in the material, is the cause for the Raman backscatter components.
The Raman scattered light consists of two components, the so-called stokes line and the anti-stokes line. Said two spectral lines lie symmetrically to the peak of the Rayleigh backscatter, shifted by a certain amount of the wave number. While the intensity of the stokes line I
S
shifted to smaller wave numbers is virtually temperature-independent, the anti-stokes line I
A
shifted to higher wave numbers is clearly dependent on the temperature, whereby the utilization of the Raman backscatter is pre-destined for the distributed temperature measurement.
The sole consideration of the information contained in the backscatter spectrum of an optical waveguide does not yet provide any information on the local distribution along the optical waveguide. The so-called OTDR method is used for backscatter measurements for the locally resolved detection of the attenuation by means of the Rayleigh scattering. In order to be able to realize a distributed, i.e. locally resolved detection of the temperature by means of the Raman sensing mechanism, either the aforementioned OTDR method (Optical Time Domain Reflectometry) is used as time domain reflectometry measurement or the OFTR (Optical Frequency Domain Reflectometry) is used as frequency domain reflectometry measurement.
The OTDR method is based on a pulse/echo principle, i.e. the intensity (scatter level) and the place of origin (scatter location) of the backscattered Raman light are determined on the basis of the time interval between sending and detecting the light impulses.
The alternative OFTR technology enables a quasi permanent operation of the laser and a narrow-band detection of the optical backscatter behavior. The so obtained advantages enable the use of more inexpensive laser light sources and cost-saving electronic components for the signal detection. In contrast thereto, however, the more problematical measurement of the scattered light and a signal processing with higher linearity requirements, which is more laborious due to the Fourier transformation, have to be taken into account.
The German laid-open print DE 195 09 129 A1 discloses a method and a device for controlling and monitoring the state of pipes, containers, pipelines and the like.
According to said teaching it is assumed that the liquid or gaseous media contained in said pipes, containers or pipelines have a different media temperature relative to the direct ambience. The ambient temperature distribution is determined at least above sections along and/or peripheral of and/or in the bottom region close to the pipes, containers, pipelines or the like, however, externally of the media space enclosed thereby.
Said temperature determination is performed with an elongated distributed temperature sensor in the form of a fiber-optic sensor cable for detecting the temperature on the basis of the aforementioned principles. If a local anomaly in the temperature distribution is detected, a leakage is assumed and the location, the direction of spreading and the leakage quantity are then determined from the temperature distribution at the respective location of the anomaly or the changing location of the anomaly.
In respect of the device according to DE 198 09 129 A1 the elongated temperature sensor, i.e. the fiber-optic sensor cable is arranged directly at or adjacent over a predetermined clearance within a pipe trench or a pipe bridge longitudinally of the pipe at the circumference of the outer surface of said pipe.
With substantially horizontally extending pipes, pipelines or the like the elongated sensor is fixed underneath the pipes. In this respect it is useful to also fix a plurality of temperature sensors or cables, which extend essentially parallel, parallel to the longitudinal axis underneath thereof so that the spreading direction and the spreading quantity of a media discharge caused by a leakage can be determined. At particularly endangered spots the aforementioned solution suggests to provide several or more densely arranged temperature sensors in order to also identify smallest leakages with a high location-related measurement accuracy.
The basis for leakage detection is the knowledge that a penetrating medium having a higher or lower temperature in relation to the ambient temperature results in a local temperature change, which also includes the direct ambience of the pipe or container jacket.
The advantageously used fiber-optic sensor cables known per se can evaluate the time interval and intensity of backscattered light with cable lengths of up to 10 km, arriving at a temperature resolution of 0.1° C. The given resolution of the location lies within 1 and 0.25 m in response to the length of the sensor cable and the selected method.
The German utility model G 93 18 404 discloses a device for determining temperatures on or in extended measurement objects, wherein the system shown therein uses an optic-electronic measurement device. Said known measurement device feeds a laser impulse on at least one end of an optical waveguide and serves to examine the radiation backscattered by the optical waveguide. Due to the already explained interactions the temperature and the location can then be evaluated longitudinally of the optical waveguide in dependence on the spectrum and the time interval, wherein the longitudinal coordinates of the optical waveguide can be associated with corresponding temperature values.
For localizing leakages particularly in ascending or supply pipes of underground gas accumulators, so-called flow meter measurements have become known, wherein the gas flow from the surrounding annular space into the actual bore hole is detected. Back-pipe effects cannot be determined by means of flow measurements, as such effects do not entail a gas flow within the piping. The local resolution of known flow meter measurements is determined by the respective discrete depths in which the measurement is carried out and is, therefore, basically small.
Moreover, it has already been suggested to seal the annular spaces one after the other in selected deep areas in order to perform pressure measurements. In this case, however,
Grosswig Stephan
Kühn Katrin
GESO Gesellschaft für Sensorik, Geotechnischen Umweltschutz und
Gutierrez Diego
Kueffner Friedrich
Verbilsky Gail
LandOfFree
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