A capacitance measurement circuit for determining complex electric currents in a multi-channel capacitive sensing device includes a first sensing circuit for selectively connecting one of a plurality of sense electrodes to a common sense node and for connecting a corresponding guard electrode of the sense electrode to a common guard node, and at least a second sensing circuit. A measurement signal voltage source provides an alternating measurement voltage to the common guard node in a remotely controllable manner. A diagnostic signal voltage source provides an alternating diagnostic voltage to the common guard node in a remotely controllable manner. A current measurement circuit is connected with a signal input port to the common sense node and with a reference input port to the output port of the measurement signal voltage source.