Balanced constant current sensing circuit inherently immune to longitudinal currents

A current converter coupled to energize a pair of conductors and including:

• circuitry for detecting differential current flow while rejecting longitudinal current in the pair of conductors comprising:
• a first resistor for generating a first voltage in response to current flow in a first line of the pair of conductors,
• a second resistor for generating a second voltage in response to current flow in a second line of the pair of conductors,
• the first and second resistor each having a first and second terminal,
• means for combining the first and second resistors so that differential current flow causes the first and second voltages to be additive and longitudinal current flow causes the first and second voltage to cancel each other,
• the means for combining comprising a grounded reference node connected to a first terminal of each of the first and second resistors,
• means for accepting a reference voltage,
• means for amplifying the first voltage as summed with the reference voltage with the second voltage,
• the means for amplifying comprising an operational amplifier having an inverting and non-inverting input,
• the means for accepting the reference voltage coupling a second terminal of the first resistor to the non-inverting input, and
• the second terminal of the second resistor being connected to the inverting input.

A current converter coupled to energize a balanced transmission line including:

• current control circuitry for monitoring a current balance between send and return leads of the transmission line comprising:
• first and second current sensing means for generating voltages responsive to current levels and each coupling a ground of the balanced transmission line to the send and return leads respectively, so that voltages due to longitudinal currents nullify each other and voltages due to differential currents are additive,
• the first and second current sensing means comprising first and second resistors connected to the ground of the balanced transmission line and having their non-grounded ends connected to the send and return lead respectively and the first and second resistors being of equal magnitude,
• a reference voltage source,
• a comparator circuit,
• the reference voltage source being connected between the first resistor and the comparator circuit,
• the comparator circuit having a first terminal connected to the first current sensing means and to the reference voltage and a second terminal connected to the second current sensing means, and
• converter control means responsive to the comparator circuit.