A method for determining at least one physical parameter by means of a sensor unit that is excited by at least one periodic excitation (1.4), wherein the sensor unit has at least one detection region in which changes in the parameter in the environment of the sensor unit result in an output signal (1.7) from the sensor unit, wherein the sensor unit is connected such that, if there are no changes in the parameter in the detection region, the output signal (1.7) at the output of the sensor unit is a zero signal or a signal approximating to zero, whereas in the event of changes in the parameter in the detection region the output signal (1.7) is a signal not equal to zero and having a particular amplitude and phase, wherein in a closed-loop control circuit, the signal not equal to zero is compensated to give a zero value by a control signal (1.6) in the receive path, even if there are changes in the parameter in the detection region, for the purpose of achieving a compensated condition, wherein the control signal (1.6) is evaluated to determine the physical parameter, wherein the output signal (1.7) of the sensor unit is reduced substantially to the fundamental wave of the excitation (1.4) and the output signal (1.7) is controlled to give zero in the entire phase space by means of at least one pulse width modulation, characterized in that at least one pulse width modulation itself each generates a correction signal of variable pulse width and where appropriate variable phase, and this is summed with the output signal (1.7) of the sensor unit, and hence controls the output signal to give zero in the entire phase space, wherein the pulse width of the correction signal and/or the phase of the correction signal is determined by the deviations of the output signal (1.7) from zero. wherein the sensor unit is connected such that, if there are no changes in the parameter in the detection region, the output signal (1.7) at the output of the sensor unit is a zero signal or a signal approximating to zero, whereas in the event of changes in the parameter in the detection region the output signal (1.7) is a signal not equal to zero and having a particular amplitude and phase, wherein in a closed-loop control circuit, the signal not equal to zero is compensated to give a zero value by a control signal (1.6) in the receive path, even if there are changes in the parameter in the detection region, for the purpose of achieving a compensated condition, wherein the control signal (1.6) is evaluated to determine the physical parameter, wherein the output signal (1.7) of the sensor unit is reduced substantially to the fundamental wave of the excitation (1.4) and the output signal (1.7) is controlled to give zero in the entire phase space by means of at least one pulse width modulation, characterized in that at least one pulse width modulation itself each generates a correction signal of variable pulse width and where appropriate variable phase, and this is summed with the output signal (1.7) of the sensor unit, and hence controls the output signal to give zero in the entire phase space, wherein the pulse width of the correction signal and/or the phase of the correction signal is determined by the deviations of the output signal (1.7) from zero.