EP0261707A1
Expired / Lapsed
EP
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Measuring circuit for continuous, accurate measurement of direct and alternating current
Assignee: Holec Systemen en Componenten BV
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Filing: 1987-08-21
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Granted: —
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Expires: 2007-08-21
Abstract
Abstract The present invention relates to a measuring circuit for continuous and accurate measurement of direct and alternating currents, comprising a magnetic integrator having a transformer (T1), and an amplifier circuit (A), a magnetic modulator including two identical transformers (T2, T3), and an energizing circuit (OSC), and a peak detector (PD), connected as shown. The magnetomotive force generated by the current (i₁) to be measured is compensated by a secondary current (i₂) from the amplifier circuit (A), in such a way that the mean flux in the transformers (T1, T2, T3) becomes zero. The output circuit of the amplifier circuit (A) is provided with a non-linear resistance (not shown), through which the secondary current (i₂) is flowing for compensation of a current (i₁) in excess of the rated current of the amplifier circuit (A), such that during an excess current interval the measuring circuit operates as a conventional current transformer. For restoring the zero-flux operation after the primary excess current is removed, a circuit consisting of a saturation detector (VD) and a buffer or calibration amplifier circuit (B) is provided.
Inventors
- 👤 Maarten Groenenboom
- 👤 Antonius Johannes Van De Water
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 00:06
CPC Classifications
H; H01; H01F; H01F27/00; H01F27/42; H01F27/422; H01F27/427; G; G01; G01R; G01R15/00; G01R15/14; G01R15/18; G01R15/183; G01R15/185; G01R19/00; G01R19/18; G01R19/20; H01F29/00; H01F29/14; H01F29/143
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
211 words
Measuring circuit for continuous and accurate measurement of direct and alternating currents, comprising a transformer with a primary winding passed through by the current to be measured, a control winding, and a secondary winding, which are accommodated in the input and output circuit re spectively of an amplifier circuit, and which are connected in such a way that the flux change caused by a current variation in the primary winding is virtually eliminated by a proportionate current variation in the secondary winding, a correction circuit which works in concert with the amplifier circuit in such a way that the residual flux caused by a primary direct current is virtually eliminated by a proportionate direct current in the secondary winding, and by means of which the mean value of the flux is maintained virtually at zero under drift phenomena, and a load passed through by the secondary current, while during the occurence of a primary excess current the transformer functions as an ordinary current transformer for alternating current during the excess current interval, characterized in that connected over the output of the amplifier circuit is a non-linear resistor, through which when a particular limit voltage is exceeded the current will increase sharply if the output current of the amplifier circuit is limited.
Claim 2
Dependent Claim
211 words
Measuring circuit for continuous and accurate measurement of direct and alternating currents, comprising a transformer with a primary winding passed through by the current to be measured, a control winding, and a secondary winding, which are accommodated in the input and output circuit re spectively of an amplifier circuit, and which are connected in such a way that the flux change caused by a current variation in the primary winding is virtually eliminated by a proportionate current variation in the secondary winding, a correction circuit which works in concert with the amplifier circuit in such a way that the residual flux caused by a primary direct current is virtually eliminated by a proportionate direct current in the secondary winding, and by means of which the mean value of the flux is maintained virtually at zero under drift phenomena, and a load passed through by the secondary current, while during the occurence of a primary excess current the transformer functions as an ordinary current transformer for alternating current during the excess current interval, characterized in that connected over the output of the amplifier circuit is a non-linear resistor, through which when a particular limit voltage is exceeded the current will increase sharply if the output current of the amplifier circuit is limited.
Claim 3
Dependent Claim
21 words
Measuring circuit according to Claim 1, characterized in that the non-linear resistor consists of two Zener diodes connected back-to-back in series.
Claim 4
Dependent Claim
38 words
Measuring circuit according to Claim 1 or 2, characterized in that the non-linear resistor consists of at least one switch which bridges the output of the amplifier circuit when the rated value of the secondary current is exceeded.
Claim 5
Dependent Claim
69 words
Measuring circuit according to Claim 3, characterized in that by means of the at least one switch the output of the amplifier circuit is alternately bridged via a positive and a negative voltage source during the intervals which correspond to the intervals at which the secondary current has a positive or a negative direction, so that the voltage-time area of the voltage induced in the secondary winding is minimal.
Claim 6
Dependent Claim
31 words
Measuring circuit according to Claims 1 to 4, characterized in that the non-linear resistor (Z) is connected parallel to the series circuit of the secondary winding (W2) and the load (Rb).
Claim 7
Dependent Claim
124 words
Measuring circuit according to Claim 5, characterized in that the non-linear resistor consists of a first and a second series circuit of a switch (S1/S2) and a supply source (B1/B2), these two series circuits being connected in parallel to a series circuit of the secondary winding (W2) and the load (Rb), and in which -depending on the direction of the secondary excess current - either the switch (S1) and the supply source (B1) of the first or the switch (S2) and the supply source (B2) of the second series circuit are operational, the selection of the switch (S1/S2) and the supply source (B1/B2) of the two series circuits being such that the voltage-time area of the voltage induced in the secondary winding is minimal.
Claim 8
Dependent Claim
60 words
Measuring a circuit according to Claims 1 to 6, provided with a detection circuit by means of which the saturation state of the cores can be indicated, characterized in that during the saturation state a relaxation-oscillator circuit is closed, so that the output current of the amplifier circuit traverses its entire working range once the primary excess current is removed.
Claim 9
Dependent Claim
123 words
Measuring circuit according to Claim 7, characterized in that the correction circuit has a saturation detector (VD), a switch (S3), and a second amplifier circuit (B), the second amplifier circuit (B) being controlled by the voltage across the load (Rb), and the saturation detector (VD), after a detected saturation of the transformer core, closes the switch (S3), as a result of which a relaxation-oscillator is created, consisting of the amplifier circuit (A), the secondary winding (W2), the second amplifier circuit (B), and the switch (S3), and in which as soon as the primary excess current is removed the relaxation-oscillator controls the amplifier (A) in such a way that there is comp lete compensation for the primary current causing saturation of the transformer core.
References Cited (Backward Citations)
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