WO1998005975A1 - Method and arrangement for optically detecting an electrical variable - Google Patents

Abstract

The invention concerns a method of optically detecting an electrical variable (I), periodic dependency being established between the optical measuring signal and the electrical variable (I) to be measured. According to the invention, two optical, periodically dependent measuring signals are used to obtain an unequivocal measuring signal. The resultant measured values are used as a value pair for unequivocally allocating an absolute value of the electrical variable (I).

Description

description

Method and arrangement for the optical detection of an electrical variable

The invention relates to a method and an arrangement for optically detecting an electrical variable, in particular a current or a voltage.

To measure current and voltage in electrical systems, optical measuring arrangements are known which are based, for example, on the agneto-optical Faraday effect. Linearly polarized measuring light is transmitted through a Faraday element arranged in the vicinity of a current conductor. The magnetic field generated by the current causes the plane of polarization of the measuring light to rotate by an angle of rotation which is proportional to the path integral over the magnetic field along the path covered by the measuring light.

With a continuous increase in the current to be measured, the angle of rotation can reach a value of over 90 °, 180 °, 360 °, and even a multiple thereof, so that with a simple determination of the angle of rotation during evaluation, no clear statement about the absolute value of the angle of rotation is possible . For this reason, only changes in the angle of rotation in a clear range, e.g. up to 90 °, approved and evaluated accordingly accordingly.

From EP 0 208 593 B1 a magneto-optical Stro wand 1er is known, in which linearly polarized measuring light

Passing through a Faraday optical fiber surrounding a current conductor is divided by a beam splitter into two partial light signals and each of these light signals is fed to an analyzer. The natural axes of the two analyzers are at an angle of 0 ° or 45 ° to the coupling polar sation of the measuring light aligned. This results in a first, sinusoidal signal at the output of one analyzer and a second, cosine-shaped signal at the output of the other analyzer.

These two signals are in each case ambiguous, oscillating functions of the current in the current conductor, which are phase-shifted from one another by an angle of 90 °. From these two ambiguous signals, a unique measurement signal is now composed by comparing the sign and the magnitude of the measured value of the first sinusoidal signal and the second cosine-shaped signal. As soon as the amounts of sine and cosine are equal, i.e. with an integer multiple of 45 °, depending on the signs of sine and cosine, a switch is made from a unique branch of the first sinusoidal signal to a unique branch of the second cosine-shaped signal or vice versa. This method is an incremental method, so that the operating point at zero current must only be reset when the electronics of a current transformer fail. See also DE 43 34 469 AI or DE 43 42 410 AI.

German patent application 195 44 778 proposes a method which uses two partial measurements. To measure the electrical measured variable in a predetermined measuring range, a first measuring signal, which is a clear function of the measured variable above the measuring range, and a second measuring signal, which is a periodic and ambiguous function of the measured variable in the predetermined measuring range, are generated. A third measurement signal, which is unambiguous over the measurement range and which has at least the measurement resolution of the second measurement signal, is derived from the two measurement signals. In this way, an absolute value can be determined at least for the unambiguous range of the first measurement signal. In general, the State of the art according to US 4,529,875, DE 40 13 125 AI and

EP 0 290 780.

The invention has for its object to provide a method and an arrangement for measuring an electrical quantity with optical means, wherein an evaluation of the optical measurement signals beyond 90 ° is possible in a simple manner.

The object is achieved according to the invention with a method for optically detecting an electrical variable,

at least a first and a second optical measurement signal are generated as a function of the electrical variable,

the periodic dependence of the two optical measurement signals on the electrical quantity, and one period being larger and at most twice as large as the other,

- The two measurement signals serve in the sense of a pair of values to which an absolute value for the electrical quantity is assigned.

Compared to the prior art, the new method allows the measurement range to be expanded beyond the uniqueness range (1st quadrant). The electrical quantity is determined at any time without storing the previous history or the previous measured values, since there is no incremental method. It is advantageous if the periodicities of the characteristic curves of the two measurement signals are close to one another. The dependencies of the optical measurement signals should be so different that as the electrical quantity to be measured increases, the phase shift between the measurement signals changes. ben is. If necessary, the measurement signals can also have a linear or non-linear dependency, for example.

It is expedient if electrical measurement signals which serve as a pair of values are derived from the optical measurement signals. In this way, simple digital processing of measured values is possible. In addition, interference influences on the optical signal, e.g. Vibration and temperature prevented. Preprocessing to electrical signals with different algorithms can advantageously lead to an “intensity standardization”, whereby compensation for the interference effects is possible.

It is expedient if the two optical measurement signals are generated with measurement light of different frequencies. In this way, only one optical sensor or only one measuring system is required. The dependence of the Faraday effect on the wavelength of light is used. Two sensitivities are thus achieved.

The two optical measurement signals can be generated simultaneously or in succession, in particular multiplex. With a simultaneous measurement, the measurement signals can be generated simultaneously and separately. In the case of a multiplex design, fewer components are required.

The two optical measurement signals can advantageously be generated in succession by continuous change, in particular by wobble, of the periodicity of the one measurement signal. This results in a continuous transition between the two measurement signals, which in principle allows an infinite number of measurement signals, as a result of which the measurement accuracy and the uniqueness of the measurement become particularly high.

The optical measurement signals can be different

Light sensors are generated. This enables separate measurement signal generation. The measurement signals can also by means of a common light sensor are generated, which comprises two light paths. This procedure is very simple, and the outlay on components is low.

In addition, a further measurement signal can be generated whose dependence on the electrical quantity is periodic and which is used to determine the electrical quantity more precisely. In this way there is a further increase in the uniqueness and the accuracy of the measurement signal. A current or a voltage is advantageously suitable as an electrical variable.

According to the invention, the problem of the arrangement can be solved with an arrangement for detecting an electrical variable on a conductor with:

at least one first optical sensor which generates at least two optical measurement signals, the dependence of the measurement signals on the electrical quantity being periodic, and wherein one period is larger and at most twice as large as the other, and

- An evaluation device connected to the sensor, which generates an assigned absolute value for the electrical quantity for the two optical measurement signals serving as a pair of values. This arrangement is particularly simple in construction and allows a considerable expansion of the uniqueness range during the measurement. Further advantageous embodiments are specified in the remaining claims. The advantages for the method already mentioned apply mutatis mutandis to the arrangement.

The sensor can have at least two optical measurement paths with different optical properties for generating the optical measurement signals. The two measurement signals can thus be generated easily, with little effort being required for the sensor. It is easy if the two measuring paths are formed by different materials. A small size is targetable. Alternatively, the two measurement paths can have different lengths. Here the material is kept low.

The optical sensor can be designed in several parts in accordance with its number of measurement paths. This enables a simple modular structure.

The optical property of the sensor can also be switchable or changeable to generate the optical measurement signals. The sensor thus becomes an active element of the arrangement, and any number of optical measurement signals can be generated with only one sensor and its control

The sensor can advantageously generate a further measurement signal which, in addition to the pair of values, is used to generate the value for the electrical variable. The measuring accuracy and uniqueness are thus further improved.

A light source can be assigned to the sensor, the frequency of which can be changed periodically and continuously, in particular in the sense of Wobbein, in order to generate the two light signals. In principle, a continuous spectrum of measurement signals can thus be generated.

Exemplary embodiments of the invention, further details and advantages are explained in more detail below with reference to the drawing. Show it:

1 shows an arrangement for the optical detection of an electrical signal and FIG. 2 shows a characteristic curve diagram for two measurement signals.

First of all, the new method is generally explained using a schematic diagram of an arrangement according to FIG. 1. aim The new method is to enable a unambiguous measurement based on ambiguous measurement signals with polarized sensors.

1 shows a conductor 1, which carries a current I with a voltage U. A sensor 3 is arranged on the conductor 1 and operates on an optical basis. The mode of operation can be based, for example, on the Faraday effect or on the Pockels effect. It is important to detect the current I or the voltage U. In the present case, current detection is assumed as an example.

The sensor 3 is connected via a light guide 5 to a light source 7, which supplies the sensor 3 with a polarized light. The polarization of the polarized light is changed in the sensor 3 as a function of the electrical quantity I, in particular rotated in its plane of polarization, and then fed to an evaluation device 11 via a second light guide 9. It is of course also possible to use arrangements in which the sensor, polarizer and analyzer form a structural unit.

The generated rotation of the polarization plane in the measurement signal is determined in the evaluation device 11. The rotation is a measure of the electrical quantity to be detected.

In the present case, the first sensor 3 delivers a periodic output signal. This means that the measurement signal is no longer unambiguous for electrical variables that cause a phase shift beyond 90 °. Proceed as follows to clearly record the electrical quantity:

First, two optical measurement signals are generated. The dependence of the two optical measurement signals on the electrical magnitude, namely the current I, is periodic, however, one period is larger, but at most twice as large as the other. This results in only a slight difference in sensitivity when the electrical quantity is measured twice.

According to the current value of the electrical quantity, different amplitude values result for the two optical measurement signals due to the different sensitivities during the detection, which are not unique in themselves. Subsequent processing or evaluation of these two values can be used to determine the absolute values of the electrical variable on the basis of mathematical considerations or with the aid of table comparisons or assignments. The sensitivities or dependencies of the two measurement signals are such that when the electrical quantity to be measured changes, there is a change in the phase shift between the measurement signals.

Various methods are available for generating the two optical measurement signals. For example, light source 7 can emit measuring light of different frequencies. This can be done simultaneously, so that the two optical measurement signals can also be detected simultaneously. Alternatively, a multiplex procedure (relating to the light transmitter or evaluation device) is also conceivable. A change in the light frequency after a wobble process can also be favorable.

Starting from a measuring light of only one frequency, which is fed to the sensor 3, it is also conceivable that the sensor 3 itself is designed to form the two optical measuring signals. For this purpose, it can comprise, for example, two light paths, both of which have different optical properties, to which a common measuring light is supplied. In the simplest case, for example, a fiber spool would be conceivable, which has a tap, so that there are two outputs. In this way, light paths of different lengths were formed. Of course, two completely separate light paths are also possible, which are formed by the same materials of different dimensions or by different materials. In principle, the sensitivity of the sensor can be set with the number of turns of the fiber spool.

1 shows a further variant in a broken line representation of a control device 13, which enables the first sensor 3 to be controlled or switched over via an action line 15. This version would offer itself for a multiplex measurement value acquisition, in which the optical properties of the sensor 3 are continuously switched over or continuously reversed, so that different measurement signals are generated alternately. Of course, the evaluation device 11 must be synchronized with the control device 13 for this purpose. As an alternative to this, switchability or continuous reversal of the light source 7 is also possible.

2 shows a diagram with two characteristic curves Ml and M2 of two measurement signals. The measurement signal here can be understood to be the optical measurement signals or electrical measurement signals already derived therefrom, which are usually used for electronic, in particular digital measurement value processing.

The characteristic curves Ml and M2 represent amplitude curves corresponding to the change in the angle of rotation as a function of the electrical variable to be measured. It can be seen that both characteristic curves Ml and M2 are periodic between a minimum and a maximum value Min or Max, and have a slightly different period.

The characteristic curves shown represent the characteristic diagrams for the acquisition of the two optical measured values.

For a given value of the electrical quantity, however, the respective amplitude values are not unique per se.

In principle, a unique value can be determined using two

Determine variables. For this purpose, it is advantageous if the period durations of the two characteristic curves lie close together, so that a clear detection is possible for many quadrants.

One way of determining the exact value is to determine the phase shift of the characteristic curves from both signals. The phase shift and thus the

The value of the electrical quantity can be e.g. determine according to the following relationship:

Value of the electrical size

In it, PI and P2 mean the values of the measured signals determined in the sense of a pair of values and K a predeterminable factor.

A further possibility for determining the absolute value of the electrical quantity would be possible by comparing the determined measured values with stored value pairs. For this purpose, the measured values can be used as a table address to find the corresponding value of the electrical quantity. In addition, a comparison of the polarities of the respective amplitude values and the difference in the amplitudes could be used to determine the electrical magnitude. The absolute value of the electrical quantity can also be determined in a direct manner, namely by calculation from the two existing measured values using general mathematical methods with appropriate algorithms.

If necessary, it is also advantageously possible to take the Hull curve of the beat of the two characteristic curves into account, as a result of which the electrical quantity is clearly determined. In principle, this basic idea is at least taken into account in the above-mentioned relationship.

With future materials and process methods, a clear measurement generation or acquisition using a controllable sensor may also be conceivable, which modulates the measurement light by suitable methods and can thus generate further measurement information, e.g. the temperature, if necessary.

Of course, the listed features of the method and the arrangement can be combined with one another or with features according to the prior art, without leaving the basic idea of the present idea. It is essential for this that, based on two ambiguous measurement signals, a conclusion can be drawn about the original electrical signal Great is given.

A preferred application of the measuring method and the arrangement is given in the optical current and voltage measurement, in particular for high or medium voltage. As a result, measurement size detection for a large measurement range can be achieved with only one sensor.

Claims

claims 1. A method for the optical detection of an electrical variable, wherein at least a first and a second optical measurement signal are generated as a function of the electrical variable, the dependencies of the two optical measurement signals on the electrical quantity are periodic, and one period is larger and at most twice as large as the other, - The two measurement signals serve in the sense of a pair of values to which an absolute value for the electrical quantity is assigned. 2. The method according to claim 1, wherein electrical measurement signals are derived from the optical measurement signals, which serve as a pair of values. 3. The method according to claim 1 or 2, wherein the two optical measurement signals are generated with measurement light of different frequency. 4. The method according to claim 1, 2 or 3, wherein the two optical measurement signals are generated simultaneously or in succession, in particular multiplex. 5. The method according to claim 4, wherein the two optical measurement signals are successively generated by continuous change, in particular by wobble, of the periodicity of the one signal 6. The method according to any one of claims 1 to 5, wherein the optical measurement signals are generated by means of different light sensors. 7. The method according to any one of claims 1 to 5, wherein the optical measurement signals are generated by means of a common light sensor (3) which comprises two light paths. 8. The method according to any one of claims 1 to 7, wherein a further optical measurement signal is generated, the dependence on the electrical variable is periodic and which is used for more accurate determination of the electrical variable. 9. The method according to any one of claims 1 to 8, wherein the electrical variable is a current or a voltage. 10. Arrangement for detecting an electrical quantity (I) on a conductor (1) with: - at least one first optical sensor (3) which generates at least two optical measurement signals, the dependence of the measurement signals on the electrical quantity (I) being periodic , and one period being larger and at most twice as large as the other, and - an evaluation device connected to the sensor (3) (11), which generates an assigned absolute value for the electrical quantity (I) for the two optical measurement signals serving as a pair of values. 11. The arrangement according to claim 10, wherein in the evaluation device (11) the two optical measurement signals are converted into electrical measurement signals which serve as a pair of values. 12. The arrangement according to claim 10 or 11, wherein the sensor (3) at least two optical measurement paths of different optical Has property for generating the optical measurement signals. 13. Arrangement according to claim 12, wherein the two measuring paths are formed by different materials. 14. Arrangement according to claim 12 or 13, wherein the two measuring paths have a different length. 15. The arrangement according to claim 12, 13 or 14, wherein the optical sensor (3) is designed in several parts according to its number of measurement paths. 16. The arrangement according to claim 10 or 11, wherein the sensor (3) for generating the optical measurement signals in its optical property is switchable or changeable. 17. Arrangement according to one of claims 10 to 16, wherein the sensor (3) is associated with a light source (7), which can be changed periodically continuously to generate the two light signals, in particular in the sense of wobble. 18. Arrangement according to one of claims 10 to 17, wherein the sensor (3) generates a further optical measurement signal, which is used in addition to the pair of values to generate the value for the electrical variable (I).