Evaluation circuit for a current sensor using the compensation principle, in particular for measuring direct and alternating currents, and a method for operating such a current sensor

A method for operating a current sensor according to the compensation principle, in particular for measuring direct and alternating currents, comprising the steps of:

• passing a current to be measured through a primary winding of a magnet core, thereby generating a primary magnetic field,
• passing a compensation current through a secondary winding of the magnet core, thereby generating a compensation magnetic field,
• controlling the compensation current so as to cause a total magnetic flux produced by the primary magnetic field and the compensation magnetic field to be zero,
• detecting deviations of the total magnetic flux from zero with a magnetic field probe and converting the detected deviations into a pulsed drive signal and amplifying the pulsed drive signal to obtain the compensation current,
• wherein the pulsed drive signal is derived from the probe current by the following steps:
• exciting the magnetic field probe with a probe current at a predetermined frequency, thereby obtaining at least one potential that depends on the probe current,
• converting the at least one potential into at least one digital signal having discrete values by evaluating differences in potential,
• measuring characteristic time values of the at least one digital signal in the form of discrete values and discrete times,
• digitally controlling the magnetic flux to a zero value by using the at least one measured time value, in particular by PI control, and
• deriving binary switching signals, in particular by using pulse-width modulation (PWM) and/or sigma-delta modulation of a first or higher order.

In a current sensor using the compensation principle, in particular for measuring direct and alternating currents, wherein the current sensor includes a magnet core having a primary winding and a secondary winding, with a current flowing through the primary winding producing a primary magnetic field and a compensation current flowing through the secondary winding producing a compensation magnetic field, at least one magnetic field sensor detecting a total magnetic flux produced by the primary magnetic field and the compensation magnetic field and producing a sensor signal, and an amplifier device controlling the compensation current in response to a switched drive signal,

• an evaluation circuit is connected between the magnetic field sensor and the amplifier device and producing the switched drive signal in response to the sensor signal, said evaluation circuit comprising
• a first oscillator with a predetermined frequency that excites the magnetic field sensor,
• at least one resistor located at a point traversed by the magnetic field sensor current and generating at least one potential dependent on a current flowing through the magnetic field sensor,
• at least one comparator that converts the at least one potential into at least one digital signal having a discrete value by comparing the at least one potential with at least one threshold value,
• at least one counter measuring characteristic time values of the at least one digital signal at discrete values and discrete times,
• a digital controller, in particular a PI controller, that controls the magnetic flux to zero by using at least one of the measured characteristic time values, and
• at least one of a second oscillator, in particular for pulse-width modulation, and a sigma-delta modulator operating in a first or higher order for deriving the pulsed drive signal for the amplifier device.

In a current sensor using the compensation principle, in particular for measuring direct and alternating currents, wherein the current sensor includes a magnet core having a primary winding and a secondary winding, with a current flowing through the primary winding producing a primary magnetic field and a compensation current flowing through the secondary winding producing a compensation magnetic field, at least one magnetic field sensor detecting a total magnetic flux produced by the primary magnetic field and the compensation magnetic field and producing a sensor signal, and an amplifier device controlling the compensation current in response to a switched drive signal,

• an evaluation circuit connected between the magnetic field sensor and the amplifier device and producing the switched drive signal in response to the sensor signal, said evaluation circuit comprising
• a first oscillator with a predetermined frequency that excites the magnetic field sensor,
• at least one resistor located at a point traversed by the magnetic field sensor current and generating at least one potential dependent on a current flowing through the magnetic field sensor,
• at least one comparator that converts the at least one potential into at least one digital signal having a discrete value by evaluating potential differences,
• at least one counter measuring characteristic time values of the at least one digital signal at discrete values and discrete times,
• a digital controller, in particular a PI controller, that controls the magnetic flux to zero by using at least one of the measured characteristic time values, and
• at least one of a second oscillator, in particular for pulse-width modulation, and a sigma-delta modulator operating in a first or higher order for deriving the pulsed drive signal for the amplifier device.

A current sensor using the compensation principle, in particular for measuring direct and alternating currents, comprising:

• a magnet core having a primary winding and a secondary winding, with a current flowing through the primary winding producing a primary magnetic field and a compensation current flowing through the secondary winding producing a compensation magnetic field,
• at least one magnetic field sensor detecting a total magnetic flux produced by the primary magnetic field and the compensation magnetic field and producing a sensor signal,
• an amplifier device controlling the compensation current in response to a switched drive signal,
• an evaluation circuit connected between the magnetic field sensor and the amplifier device and producing the switched drive signal in response to the sensor signal, said evaluation circuit comprising
• a first oscillator with a predetermined frequency that excites the magnetic field sensor,
• at least one resistor located at a point traversed by the magnetic field sensor current and generating at least one potential dependent on a current flowing through the magnetic field sensor,
• at least one comparator that converts the at least one potential into at least one digital signal having a discrete value by comparing the at least one potential with at least one threshold value or by evaluating potential differences,
• at least one counter measuring characteristic time values of the at least one digital signal at discrete values and discrete times,
• a digital controller, in particular a PI controller, that controls the magnetic flux to zero by using at least one of the measured characteristic time values, and
• at least one of a second oscillator, in particular for pulse-width modulation, and a sigma-delta modulator operating in a first or higher order for deriving the pulsed drive signal for the amplifier device.