Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1999-03-19
2000-10-31
Dang, Hung Xuan
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25022724, H01J 4014
Patent
active
061406341
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a sensor for measuring electrical properties selected from a group consisting of current strength and voltage. The sensor includes a source of testing light with a particular parameter; an optical transparent medium being arranged in an electrical field, which surrounds a conductor and is produced by the electricity flowing in the conductor, the testing light being sent through the medium to experience a change in the parameter that is determined by defined optical material constants of the medium, which constants depend on the temperature of the medium and the particular field strength of the electromagnetic field; an evaluation means to obtain a quantity of the modifications of the parameter of the testing light passing through the medium so that the current strength can be determined with the aid of the quantity and the material constant.
Sensors of the named type are known and are of interest for energy measurement tasks. Sensors of this type are mostly used for measuring current strength and/or voltage of alternating current.
A problem in sensors of this type is the material constant of the optically transparent medium intended for the measurement, which constant is dependent on the temperature of this medium, by means of which constant a required measurement precision cannot be achieved.
In order to take into account this material-specific temperature dependence, it is known to arrange an external conventional temperature sensor on the medium intended for the measurement, which sensor measures the temperature of this medium immediately. The electrical current strength to be measured can then be determined with the material constant allocated to this measured temperature.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a sensor of the type named above in which the temperature dependence of the material constant can be taken into account without an external temperature sensor.
This object is achieved by an improvement in the sensor. The improvement comprises a fluorescing medium being arranged close to the optical transparent medium so as to be at the same temperature as the medium, said fluorescing medium emitting a fluorescent light when excited by an exciting light, said fluorescent light having an intensity decaying after termination of the exciting light with the decay time being dependent on the temperature of the fluorescing medium, a source of exciting light; means for radiating the exciting light onto the fluorescing medium; and fluorescent light evaluation means for determining the decay time of the fluorescent light to obtain the temperature and Verdet constant which are used to determine the electrical current strength in the conductor.
According to the invention, the particular material constant belonging to a particular temperature of the optically transparent medium and that is to be used for the determination of the current strength and/or voltage is determined by determining the decay time of the fluorescent light produced in the fluorescing material by the intensity-modulated exciting light.
The inventive sensor is suited in particular for optically transparent media in which no additional temperature-dependent effect occurs, other than the temperature dependence of the optical material constant of this medium. This also holds in particular for a magneto-optical sensor in which measurement takes place in the optically transparent medium with the aid of the Faraday effect, and the optical material constant of this medium is the Verdet constant.
Further temperature-dependent effects are for example linear and circular birefringence effects in the optically transparent medium that change with the temperature and that obscure the material-specific temperature dependence of the material constant by means of superposition.
It is useful to arrange the fluorescing material used in the inventive sensor in a light path of the light under test produced by the source of the light under test, said path leading from
REFERENCES:
patent: 6043648 (2000-03-01), Menke et al.
Laming et al. "Electric Current Sensors Employing Spun Highly Birefringent Optical Fibers", Journal of Lightwave Technology, vol. 7, No. 12, Dec. 1989, pp. 2084-2094.
Dang Hung Xuan
Siemens Aktiengesellschaft
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