Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Reexamination Certificate
2002-04-01
2004-05-11
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
C324S11700H, C324S142000
Reexamination Certificate
active
06734661
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to current sensors for measuring current flowing in conductors. More particularly, but not exclusively, the invention relates to a current sensor forming part of an alternating current (AC) fiscal electricity meter for measuring the energy supplied by a utility company.
BACKGROUND TO THE INVENTION
In a published PCT patent application PCT/GB00/02851 (WO 01/11376), there is described a current sensor which responds to a magnetic field generated by a current flowing in a load conductor.
In a published U.S. Pat. No. 4,894,610, there is described a current-transformer arrangement for a static electricity meter.
In a published PCT patent application no. PCT/GB00/02604, there is described an electronic circuit formed on a printed circuit board which is configured as a current-to-voltage converter using a printed circuit track as a sensor, the sensor being placed in parallel with a primary current carrying conductor, for example a bus bar.
Situations arise where a current sensor is required having the following characteristics:
(a) a load current bearing conductor having a simple linear shape;
(b) a sensor scaling factor susceptible to modification merely by altering dimensions of the sensor in one direction;
(c) a circuit board real estate which is used efficiently and is substantially rectangular in format with a minimum number of vias and/or cross-overs; and
(d) virtual immunity to remotely generated alternating magnetic fields.
Current sensors described in the aforesaid PCT applications and US patent are not capable of providing simultaneously all the characteristics (a) to (d) above.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a current sensor for measuring current flowing between a power source and a load, the sensor comprising:
an inlet for connection to the source;
an outlet for connection to the load;
conductor paths connected between the inlet and the outlet for guiding currents through the sensor; and
sensing means associated with each conductor path for sensing current flowing therethrough and for generating a corresponding current measure indicative of the magnitude of the current,
characterised in that each sensing means comprises an array of elongate conductive elements which are, firstly, so arranged as to be each mutually dissimilarly coupled to the local magnetic field generated, in use, by current flowing through the associated conductor path and, secondly, so interconnected as to render the sensing means substantially insensitive to magnetic fields generated remotely therefrom.
Such a sensor is capable of one or more of the following:
(a) operating in conjunction with a load current bearing conductor having a simple linear shape;
(b) providing a sensor scaling factor susceptible to modification merely by altering dimensions of the sensor in one direction;
(c) occupying a circuit board real estate which is used efficiently and is substantially rectangular in format with a minimum number of vias and/or cross-overs; and
(d) being substantially immune to remotely generated alternating magnetic fields.
Preferably, the one or more conductive paths are disposed to couple their magnetic fields generated in response to the one or more currents flowing therethrough preferentially to a subset of the zones, thereby generating a residual signal indicative of the magnitude of the one or more currents, the residual signal for use in providing the current measure. Preferentially coupling to a subset of the zones is of advantage in that the zones can be arranged to provide a substantially negligible response to uniform magnetic fields generated by sources remote to the sensor to render the sensor substantially insensitive to such uniform fields, whilst providing measuring sensitivity by virtue of preferentially coupling magnetic fields generated by the one or more currents to the subset of zones.
The one or more conductive paths are preferably implemented as one or more substantially-linear elongate conductive members in proximity of the zones and are arranged to couple magnetically preferentially to one or more of the zones. Incorporation of such substantially-linear conductive members is of advantage in that they are easier to manufacture in comparison to conductive members of complex shape, for example conductive members including circular current paths.
Preferably, the one or more elongate conductive members are integral with the elongate elements on an insulating substrate. Integral mounting of the one or more elongate members onto the substrate is of advantage in that measurement sensitivity of the sensor is dramatically enhanced in comparison to spaced-apart mounting of the elongate members with respect to the substrate.
Alternatively, the one or more elongate conductive members are preferably disposed spatially mutually separated from the elongate elements by a gap region. Such a separated configuration is of advantage in that the sensor is capable of operating with a greater potential difference between the one or more members and the elongate elements.
The zones are preferably implemented as elongate regions comprising coil elements. Such elongate disposition of the elongate regions assists to enhance the measurement sensitivity of the sensor in comparison to a non-elongate implementation of the sensor.
Preferably, to improve manufacturability and reduce cost, the elongate elements are implemented in the form of conductive tracks on a printed circuit board.
On account of the use of a transformation described later, it is feasible to reduce the need for track cross-overs and thereby largely circumvent the need to use circuit board vias. Thus, the elongate elements of the sensor are preferably interconnected on the circuit board substantially without the need to use vias.
More preferably, the printed circuit board is a multi-layer board and the elongate coil elements are duplicated at a plurality of levels in the board and corresponding overlaid zones coupled together in order to enhance current measuring sensitivity of the sensor.
For example, the elongate coil elements are preferably duplicated at several of the layers in the form of a stack and connected in series to provide an increase in output signal magnitude resulting from magnetic fields generated by current flow in the one or more conductive paths coupling into the stack.
Preferably, elongate coil elements of the overlaid zones are interconnected at regions remote from where the one or more load conductors couple magnetically to one or more of the elements. Implementing interconnection at regions remote for active coupling zones of the sensor enables a greater sensor measurement sensitivity to be achieved.
Insensitivity of the sensor to uniform remotely-generated magnetic fields is an important performance characteristic of the sensor. Especially when the sensor is implemented comprising a stack of elongate coil elements, there is tendency for the sensor to become sensitive to uniform magnetic fields incident parallel to the plane of the sensor. By alternately swapping connection of elongate elements in the several layers, it is possible to arrange for EMFs generated by in-plane uniform fields to mutually oppose rendering the sensor substantially immune to such uniform fields. Thus, preferably, the elongate coil elements are connected alternately between layers so as to render the sensor less sensitive to uniform magnetic fields incident on the sensor having field components parallel to the plane of the sensor.
Conveniently, in order to render the sensor more efficient in its use of circuit board real estate, the elongate coil elements are preferably arranged so that their elongate axes are substantially mutually parallel.
In order for the sensor to provide a substantially linear measurement response for a wide range of currents conveyed through the sensor to the load, the elongate coil elements are preferably non-ferromagnetically coupled to the one or more conductive paths. The use of ferromagnetic components in the sensor
Colby Edward Grellier
Storkey Matthew Emmanuel Milton
Karlsen Ernest
Lilling & Lilling P.C.
Sentec Limited
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