Electromagnetic type measuring apparatus for digitally measuring electric conductivity

Claim 2

In an electromagnetic induction type conductivity measuring apparatus of the type comprising a first magnetic core, a first coil wound on said first magnetic core, a source of alternating current, first switch means for supplying an exciting current to said first coil, a second magnetic core, a second coil wound on said second core, a voltage divider connected across said source for impressing a predetermined proportion of the voltage of said source across said second coil, and an output coil wound on said second core, said first and second cores being adapted to be immersed in conductive liquid whose conductivity is to be measured, the improvement which comprises rectifier means coupled to said output coil through the same signal channel for rectifying the voltage induced in said output coil to produce rectified outputs of positive and negative polarities, an integrator, second switch means for selectively supplying the positive or negative rectified output to said integrator, a comparator operable in response to successive opposite polarity intervals of said rectified output applied to said integrator for comparing the output from said integrator with a zero potential, and a pulse counter controlled by the output from said comparator whereby to provide a digital output corresponding to the conductivity of said liquid.

Claim 3

Apparatus according to claim 1 in which said first and second switch means are operable to alternately accumulate a first quantity in said integrator in response to one of said polarities representative of the conductivity of said liquid and to integrate in equal second quantity in response to the other said polarity representative of said predetermined proportion to obtain an output quantity substantially independent of circuit parameters representative of said conductivity.

Claim 4

Apparatus according to claim 2 in which said first quantity is representative of the difference between the signal induced in said second core by the conductivity of said fluid and that impressed on said second coil.

Claim 5

An electromagnetic induction type conductivity measuring apparatus comprising a first magnetic core, a first coil wound on said first magnetic core, a source of alternating current, first switch means for selectively supplying an exciting current to said first coil, a second magnetic core, a second coil wound on said second core, a voltage divider selectively connected across said source for impressing a predetermined proportion of the voltage of said source across said second coil, and an output coil wound on said second core, said first and second cores being adapted to be immersed in conductive liquid whose conductivity is to be measured, rectifier means coupled to said output coil through the same signal channel for rectifying the voltage induced in said output coil to produce rectified outputs for each position of said switch of positive and negative polarities, an integrator, second switch means operating in conjunction with said first switch means for selectively supplying the positive or negative rectified output to said integrator, a comparator operable in response to successive opposite polarity intervals of said rectified output applied to said integrator for comparing the outPut from said integrator for two successive switch intervals with a zero potential, and a pulse counter controlled by the output from said comparator whereby to provide a digital output corresponding to the conductivity of said liquid that is substantially independent of circuit parameters.

Claim 6

An electromagnetic induction type conductivity measuring apparatus comprising a first magnetic core, a first coil wound on said first magnetic core, a source of alternating current, first switch means for selectively supplying an exciting current to said first coil, a second magnetic core, a second coil wound on said second core, a voltage divider selectively connected across said source for impressing a predetermined proportion of the voltage of said source across said second coil, and an output coil wound on said second core, said first and second cores being adapted to be immersed in conductive liquid whose conductivity is to be measured, rectifier means coupled to said output coil through the same signal channel for rectifying the voltage induced in said output coil to produce rectified outputs for each position of said switch of positive and negative polarities, an integrator, second switch means operating in conjunction with said first switch means for selectively supplying the positive or negative rectified output to said integrator, a comparator operable in response to successive opposite polarity intervals of said rectified output applied to said integrator for comparing the outPut from said integrator for two successive switch intervals with a zero potential, and a pulse counter controlled by the output from said comparator whereby to provide a digital output corresponding to the conductivity of said liquid that is substantially independent of circuit parameters.

Claim 9

The method according to claim 5 in which said integration signals are representative of the difference between said second and third magnetic fluxes and said third magnetic flux.