METHOD OF AND APPARATUS FOR IMPROVING THE LINEARITY OF THE CURREnT TRANSFORMATION OF A DC MEASURING TRANSDUCTOR

Claim 2

In a device for measuring direct current flowing in a conductor, which device comprises: primary winding means for current conductive connection to said conductor; magnetic core means coupled with said primary winding means for establishing a first flux field in said core means which is proportional to the direct current flowing in said conductor; a measuring circuit comprising in series connection secondary winding means coupled with said core means, alternating voltage generator means, rectifying means and load impedance means for establishing in said core means a varying second flux field opposing said first flux field during at least part of the alternating voltage cycle; in combination: flux variation detecting means for detecting the flux variation of said second flux field in said core means during said part of the alternating voltage cycle; control means connecting said flux variation detecting means to said generator means for so varying the output of the latter as to maintain said flux variation at a constant value irrespective of the current flowing in said conductor; and d.c. bias means connected to said load impedance means for compensating fixed current error created by maintaining the variation of said second flux field at a constant value.

Claim 3

In a device for measuring direct current as defined in claim 1 wherein said control means includes a source of reference voltage and comparator means connected to said flux variation detecting means and to said source of reference voltage for controlling said generator means.

Claim 4

In a device for measuring direct current as defined in claim 2 wherein said flux variation detecting means comprises a pick-up winding coupled to said transformer core means.

Claim 5

In a device for measuring direct current as defined in claim 3 wherein said flux variation detecting means also includes an integrator connected in series with said pick-up winding.

Claim 6

In a device for measuring direct current as defined in claim 4 wherein said pick-up winding forms at least a part of said secondary winding means.

Claim 7

In a device for measuring direct current as defined in claim 4 wherein said pick-up winding is separate from said secondary winding means.

Claim 8

In a device for measuring direct current as defined in claim 1 wherein said flux variation detecting means comprises a pick-up winding coupled to said transformer core means.

Claim 9

In a device for measuring direct current as defined in claim 7 wherein said flux variation detecting means also includes an integrator connected in series with said pick-up winding.

Claim 10

In a device for measuring direct current as defined in claim 8 wherein said pick-up winding forms at least part of said secondary winding means.

Claim 11

In a device for measuring direct current as defined in claim 8 wherein said pick-up winding is separate from said secondary winding means.

Claim 12

A d.c. current transformer device for measuring the amplitude of d.c. current flowing in a conductor, comprising in combination: transductor means having secondary d.c. output terminal means, said transductor means including transformer coil means of ferromagnetic material coupled with said conductor for receiving primary d.c. current input which creates a first flux field in said core means, secondary winding means coupled with said core means for creating a second fLux field in said core means, alternating voltage generator means and rectifier means connected to said secondary winding means and to said output terminal means for causing said second flux field variably to oppose said first flux field at least during alternate half cycles of said generator means, and load impedance means connected to said output terminal means for carrying secondary d.c. current drawn by said secondary winding means in creating said second flux field, said alternating voltage generator means being controllable as to its voltage-time product output; control means connecting said flux variation detecting means to said alternating voltage generator means for controlling the voltage-time product output of the latter to maintain the variation of said second flux field at a constant value irrespective of the amplitude of said primary d.c. current, whereby said secondary d.c. current is characterized by an error of fixed value; and d.c. bias means connected to said load impedance means for compensating said error of fixed value.

Claim 13

A d.c. current transformer device for measuring the amplitude of d.c. current flowing in a conductor, comprising in combination: transductor means having secondary d.c. output terminal means, said transductor means including transformer coil means of ferromagnetic material coupled with said conductor for receiving primary d.c. current input which creates a first flux field in said core means, secondary winding means coupled with said core means for creating a second fLux field in said core means, alternating voltage generator means and rectifier means connected to said secondary winding means and to said output terminal means for causing said second flux field variably to oppose said first flux field at least during alternate half cycles of said generator means, and load impedance means connected to said output terminal means for carrying secondary d.c. current drawn by said secondary winding means in creating said second flux field, said alternating voltage generator means being controllable as to its voltage-time product output; control means connecting said flux variation detecting means to said alternating voltage generator means for controlling the voltage-time product output of the latter to maintain the variation of said second flux field at a constant value irrespective of the amplitude of said primary d.c. current, whereby said secondary d.c. current is characterized by an error of fixed value; and d.c. bias means connected to said load impedance means for compensating said error of fixed value.