Complementary sensing device for minimizing the effects of common mode voltages

Claim 2

A measurement apparatus for reducing common mode effects, comprising: first means and second means symmetrically located relative to a sample voltage of fluid for sensing a parameter associated with the sample volume, said first and second means having respective first and second impedances; third means communicating with said first means for generating a first common mode signal; fourth means communicating with said second means for generating a second common mode signal; and fifth means for combining said first and second common mode signals for reducing common mode effects.

Claim 3

An apparatus, as claimed in claim 1, wherein: said third means generates a first measurement signal relating to the parameter being sensed and said fourth means generates a second measurement signal relating to the parameter being sensed.

Claim 4

An apparatus, as claimed in claim 2, wherein: said fifth means is responsive to said first and second measurement signals and combines them to produce a combined signal representative of the parameter being sensed.

Claim 5

An apparatus, as claimed in claim 3, wherein: said fifth means includes means for adjusting the signal outputted by said fifth means.

Claim 6

An apparatus, as claimed in claim 4, wherein: said means for adjusting includes a potentiometer.

Claim 7

An apparatus, as claimed in claim 1, wherein: said third means is complementary to said fourth means wherein a first measurement signal outputted by said third means is substantially equal in magnitude to a second measurement signal outputted by said fourth means, said first and second measurement signals relating to the parameter.

Claim 8

An apparatus, as claimed in claim 1, wherein: said third means includes first voltage follower circuit means.

Claim 9

An apparatus, as claimed in claim 7, wherein: said fourth means includes second voltage follower circuit means.

Claim 10

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter; second means communicating with said first means for generating a first common mode signal, said second means includ ing first sampling resistor means; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 11

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter; second means communicating with said first means for generating a first common mode signal, said second means includ ing first sampling resistor means; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 12

An apparatus, as claimed in claim 9, wherein: said second means includes sampling resistor means.

Claim 13

An apparatus, as claimed in claim 1, wherein: said third means includes first amplifying means, the output of which communicates with said fifth means.

Claim 14

An apparatus, as claimed in claim 11, wherein: said fourth means includes second amplifying means, the output of which communicates with said fifth means.

Claim 15

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter, said first means includ ing a passageway for containing fluid having the parameter to be measured and having an axis of symmetry, said passageway being defined by a first side and a second side with each of said first and second sides being spaced an equal distance from said axis of symmetry; second means communicating with said first means for generating a first common mode signal; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 16

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter, said first means includ ing a passageway for containing fluid having the parameter to be measured and having an axis of symmetry, said passageway being defined by a first side and a second side with each of said first and second sides being spaced an equal distance from said axis of symmetry; second means communicating with said first means for generating a first common mode signal; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 17

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter, said first means includ ing a passageway for containing fluid having the parameter to be measured, a first pair of electrodes and a second pair of electrodes, wherein said first pair of electrodes and said second pair of electrodes are located symmetrically relative to said passgeway; second means communicating with said first means for generating a first common mode signal; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 18

A measurement apparatus for reducing common mode effects, comprising: first means for sensing a parameter, said first means includ ing a passageway for containing fluid having the parameter to be measured, a first pair of electrodes and a second pair of electrodes, wherein said first pair of electrodes and said second pair of electrodes are located symmetrically relative to said passgeway; second means communicating with said first means for generating a first common mode signal; third means for generating a second common mode signal; and fourth means for combining said first and second common mode signals for reducing common mode effects.

Claim 19

An apparatus, as claimed in claim 14, wherein: a first electrode of each of said first and second pairs of electrodes is maintained at a predetermined potential.

Claim 20

An apparatus, as claimed in claim 15, wherein: a second electrode of each of said first and second pairs of electrodes is disposed in a feedback path for use in maintaining the fluid near said second electrodes of said first and second pairs of electrodes at said predetermined potentials.

Claim 21

A complementary conductivity measurement apparatus for reducing common mode effects, comprising: conductivity cell means disposed in a fluid whose conductivity is to be measured, said conductivity means including a passageway and first and second pairs of electrodes, said first and second pairs of electrodes being symmetrically disposed relative to said passageway wherein said passageway has an axis of symmetry and the potential about said axis of symmetry is substantially equal to zero, said first pair of electrodes including a first electrode and a second electrode and said second pair of electrodes including a first electrode and a second electrode; first complementary measurement means communicating with said conductivity cell means, said first complementary measurement means including voltage follower circuit means, sampling resistor means and amplifying means, the output of said voltage follower circuit means communicating with said first electrode of said first pair of electrodes, said second electrode of said first pair of electrodes providing an input to said voltage follower circuit means, said sampling resistor means being responsive to said output of said voltage follower circuit means and providing an input to said amplifying means, said voltage follower circuit means for use in maintaining the fluid near said second electrode of said first pair of electrodes at a predetermined potential; second complementary measurement means communicating with said cell conductivity means, said second complementary measurement means including voltage follower circuit means, sampling resistor means and amplifying means, the output of said voltage follower circuit means communicating with said first electrode of said second pair of electrodes, said second electrode of said second pair of electrodes providing an input to said voltage follower circuit means, said sampling resistor means being responsive to said output of said voltage follower circuit means and providing an input to said amplifying means, said voltage follower circuit means for use in maintaining the fluid near said second electrode of said first pair of electrodes at a predetermined potential; and means for combining outputs from said amplifying means of said first complementary measurement means and said amplifying means of said second complementary measurement means wherein said means for combining outputs a signal relating to the magnitude of the parameter being measured while reducing common mode effects.

Claim 22

A complementary conductivity measurement apparatus for reducing common mode effects, comprising: conductivity cell means disposed in a fluid whose conductivity is to be measured, said conductivity means including a passageway and first and second pairs of electrodes, said first and second pairs of electrodes being symmetrically disposed relative to said passageway wherein said passageway has an axis of symmetry and the potential about said axis of symmetry is substantially equal to zero, said first pair of electrodes including a first electrode and a second electrode and said second pair of electrodes including a first electrode and a second electrode; first complementary measurement means communicating with said conductivity cell means, said first complementary measurement means including voltage follower circuit means, sampling resistor means and amplifying means, the output of said voltage follower circuit means communicating with said first electrode of said first pair of electrodes, said second electrode of said first pair of electrodes providing an input to said voltage follower circuit means, said sampling resistor means being responsive to said output of said voltage follower circuit means and providing an input to said amplifying means, said voltage follower circuit means for use in maintaining the fluid near said second electrode of said first pair of electrodes at a predetermined potential; second complementary measurement means communicating with said cell conductivity means, said second complementary measurement means including voltage follower circuit means, sampling resistor means and amplifying means, the output of said voltage follower circuit means communicating with said first electrode of said second pair of electrodes, said second electrode of said second pair of electrodes providing an input to said voltage follower circuit means, said sampling resistor means being responsive to said output of said voltage follower circuit means and providing an input to said amplifying means, said voltage follower circuit means for use in maintaining the fluid near said second electrode of said first pair of electrodes at a predetermined potential; and means for combining outputs from said amplifying means of said first complementary measurement means and said amplifying means of said second complementary measurement means wherein said means for combining outputs a signal relating to the magnitude of the parameter being measured while reducing common mode effects.

Claim 25

A method, as claimed in claim 18, wherein: said step of producing said second common mode signal component includes producing said second common mode signal component having a magnitude substantially equal that, and polarity substantially opposite that of said first common mode signal component.

Claim 28

A method, as claimed in claim 20, wherein: said step of generating said first measurement signal component includes driving a first electrode of said first pair of electrodes and receiving feedback from a second electrode of said first pair of electrodes.

Claim 29

A method, as claimed in claim 21, wherein: said step of generating said first measurement signal component includes amplifying a signal obtained using said first electrode.