Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1998-08-18
2001-03-27
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S11700H
Reexamination Certificate
active
06208129
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an arrangement for measuring a periodic quantity. A periodic quantity is used herein to describe a measurable quantity which, in its frequency spectrum, only has frequency components that differ from zero and is, thus, in particular, a measurable quantity that varies with time.
BACKGROUND OF THE INVENTION
PCT Application No. W/O 95/10046, describes optical measuring arrangements and measuring methods for measuring a periodic quantity, in particular for measuring a magnetic alternating field or an electric a.c. current, utilizing the magnetooptic Faraday effect, or for measuring an electric alternating field or an electric a.c. voltage utilizing the electrooptical Pockels effect. Polarized measuring light is coupled into a sensor device that is under the influence of the periodic quantity. The polarization of the measuring light is varied in the sensor device as a function of the periodic quantity. To analyze this change in polarization, after propagating at least once through the sensor device, the measuring light is split into two linearly polarized partial light signals having different polarization planes. An intensity-normalized signal P is formed, which corresponds to the quotient of a difference and the sum of the light intensities of the two partial light signals. A temperature-compensated measuring signal is derived from an alternating signal component and from a direct signal component of the intensity-normalized signal. In this context, the direct signal component does not contain any frequency components of the periodic quantity and is only used for temperature compensation.
“
Optical Combined Current
&
Voltage H.V. Sensors, GEC Alsthom
, T&D, describes a magnetooptical current transformer in which a light signal that is linearly polarized in a polarizer propagates through a Faraday glass ring and is then split by a polarizing beam splitter into two partial light signals, which are linearly polarized, transversely with respect to one another (two-channel polarization analysis). Each of the two partial light signals is fed via an optical fiber to a corresponding photodiode, which converts the partial light signal in question into an electric intensity signal S
1
or S
2
, which is proportional to the light intensity of the corresponding partial light signal. Due to the different attenuation in the two optical fibers, the two proportionality constants can differ from one another at this point. To compensate for these differences in responsivity, provision is made for a special closed-loop control. A controllable first amplifier connected downstream from the first photodiode amplifies the intensity signal S
1
by a corresponding gain K
1
, and a second amplifier connected downstream from the second photodiode amplifies the second intensity signal S
2
by a second gain K
2
. At this point, direct signal components (DC values) of the two intensity signals S
1
and S
2
are determined, and the difference between the two direct signal components is set to zero by controlling the gain K
1
of the first amplifier. From the two intensity signals K
1
·S
1
and K
2
·S
2
, which are generally amplified with varying intensity, at the outputs of the two amplifiers, a measuring signal is now formed, which corresponds to the quotient (K
1
·S
1
−K
2
·S
2
)/(K
1
·S
1
+K
2
·S
2
) of the difference and the sum of the output signals of the amplifiers.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical measuring method and an optical measuring arrangement for measuring a periodic quantity, where the polarization state of polarized measuring light in a sensor device is varied as a function of the periodic quantity, and the measuring light for analyzing this change in polarization is split, after propagating through at least once, into two variably linearly polarized, partial light signals, and undesired intensity variations in the light paths of the measuring light and of the two partial light signals are compensated.
A method for measuring a periodic quantity according to the present invention includes the following method steps:
a) polarized measuring light propagates at least once through a sensor device that is under the influence of the periodic quantity, the sensor device varying the polarization of the measuring light as a function of the periodic quantity, and is then split into two linearly polarized partial light signals having light intensities I
1
and I
2
and different polarization planes;
b) from the light intensities I
1
and I
2
of the two partial light signals and direct components I
1
DC
or I
2
DC
of these two light intensities I
1
and I
2
, a measuring signal is formed for the periodic quantity, which is essentially proportional to the quotient
(I
2
DC
·I
1
−I
1
DC
·I
2
)/(I
2
DC
·I
1
+I
1
DC
·I
2
),
the two direct components I
1
DC
or I
2
DC
not containing any frequency components of the periodic quantity.
An arrangement for measuring a periodic quantity according to the present invention includes:
a) a sensor device, which varies the polarization of polarized light as a function of the periodic quantity;
b) means for coupling polarized measuring light into the sensor device;
c) means for splitting the measuring light, after propagating at least once through the sensor device, into two linearly polarized partial light signals having different polarization planes and having light intensities I
1
or I
2
;
d) means for generating a measuring signal for the periodic quantity from light intensities I
1
and I
2
of the two partial light signals and direct components I
1
DC
or I
2
DC
of these two light intensities I
1
or I
2
, which do not contain any frequency components of the periodic quantity, the measuring signal essentially being proportional to the quotient
(I
2
DC
·I
1
−I
1
DC
·I
2
)/(I
2
DC
·I
1
+I
1
DC
·I
2
).
Because of the special consideration given to the direct signal components I
1
DC
and I
2
DC
of the two light intensities I
1
or I
2
as an index for the mentioned intensity variations in the light paths, the measuring signal is virtually completely intensity-normalized.
Accordingly, the method and the arrangement are preferably used in a first advantageous specific embodiment for measuring a magnetic alternating field, in that a sensor device indicating the magnetooptical Faraday effect is used, and the measuring signal is retrieved as an index for the magnetic alternating field.
In a second advantageous specific embodiment, the method and arrangement for measuring an electric a.c. voltage or an electric alternating field in which a sensor device indicating the electrooptical Pockels effect is used, and the measuring signal is retrieved as an index for the electric a.c. voltage or for the electric alternating field.
The two partial light signals are preferably transmitted in each case via at least one optical fiber and, in particular, via at least two optical fibers and one optical connector for detachably joining the two optical fibers. The connectors are advantageously used for temporarily disconnecting the sensor device that is generally linked to different electric potentials, on the one hand, and the evaluation electronics, on the other hand. In this specific embodiment, the measuring signal is also independent of light intensity variations in the two partial light signals in response to variations in the attenuation properties of the connectors following their opening and subsequent closing.
REFERENCES:
patent: 4973899 (1990-11-01), Jones et al.
patent: 5446381 (1995-08-01), Okajima et al.
patent: 5656934 (1997-08-01), Bosselmann
patent: 5764046 (1998-06-01), Bosselmann
patent: 43 12 183 (1994-10-01), None
patent: 43 34 469 (1995-04-01), None
patent: 43 42 410 (1995-06-01), None
patent: 0 088 419 (1983-09-01), None
patent: 0 108 671 (1984-05-01), None
patent: 0 682 261 (1995-11-01), None
patent: 02143173 (1990-06-01), None
patent: WO 95/10046 (1995-04-01), None
H. Hirsch, et al. “Nutz-und Storeffekt
Bosselmann Thomas
Hain Stefan
Menke Peter
Willsch Michael
Kenyon & Kenyon
Nguyen Vinh P.
Siemens AG
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