Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Patent
1993-12-29
1995-07-11
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
336 73, 336200, 323357, G01R 3300
Patent
active
054324394
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an arrangement in a current detection circuit, comprising a primary coil for the current to be detected, a separate transformer core which is influenced by the current of the primary coil, a secondary coil conducting a transformed secondary current, as well as a tertiary coil connected to an operational amplifier including a feed-back resistor and constituting a current-voltage converter circuit with an input resistance of nearly zero ohms.
PRIOR ART
From GB 1 404 719 there is disclosed a current measuring transformer for obtaining a voltage proportional to the current to be measured. This prior art current measuring transformer comprises a closed transformer core associated with a secondary winding which is directly short-circuited without any load impedance, and having a pick-up winding with terminals across which appears the voltage which is proportional to the current to be measured. However, the secondary winding is formed by the metal rail through which the primary current is flowing. Further, the prior art core is made up of plates and bolts which are solidly attached to the metal rail itself. Consequently, this type of measuring transformer will not be adaptable for integration in a circuit board.
From EP 0 157 881 B1 (Toda) there is disclosed a current detection circuit of the type cited in the above preamble.
According to teaching it is suggested that the prior art transformer further comprises a tertiary coil being provided with two terminals, and having these two terminals electrically connected by a conductor, so as to provide a short-circuited tertiary coil. However, the production of such a transformer requires a number of terminals, especially for the tertiary coil, i.e. a physical interface between the terminals thereof and the conductor which is to short-ciruit the tertiary coil. The prior art suggestion of having a physical interface between the terminals of the tertiary coil and the associated short-circuiting conductor is further substantiated by the fact that the prior art secondary coil and the prior art tertiary coil should be wound with the same material in parallel disposition and with substantially the same number of turns should and still further substantiated by suggesting that terminals should be provided at both ends and a middle point of one series coil, one side of which constituting the prior art secondary coil and the other side of which constituting the tertiary coil.
Such a prior art current detection circuit would not pave the way for manufacturing a current detection circuit in an integral manner on a circuit board, since this prior art transformer including a plurality of terminals and physical interfaces to be provided and connected to appropriate conductors during the manufacturing thereof, would be highly ineffective by requiring a plurality of process steps and accordingly a high output cost.
Further, this prior art detection circuit would not give the artisan any instructions for arriving at a solution which is temperature-independent in a more rational and effective manner. Although it is true that the prior art current detection circuit according to EP 0 157 881 B1 suggests that the secondary coil and the tertiary coil should be of materials of different resistance-temperature coefficient, this will only give a desired temperature characteristic to the current detection circuit, but not a highly efficient temperature-equalizing circuit.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a current detection circuit in which the elements thereof can easily be integrated in a circuit board.
A further object of the present invention is to provide a current detection circuit in which one or more coils can be provided by punching, said punching operation being very cost favourable compared with the manufacturing of wound coils.
Yet another object of the present invention is to provide a current detection circuit in which the measuring coil or tertiary coil can be integrated directl
REFERENCES:
patent: 5010314 (1991-04-01), Estrov
patent: 5321380 (1994-06-01), Godek
ABB Energi AS
Wardas Mark
Wieder Kenneth A.
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