A modified Maxwell displacement current (MDC) measurement is described. The distance between water surface and a suspended electrode is changed sinusoidally at an angular frequency omega = omega(t), hence the MDC and the induced charge on the suspended electrode are modulated. The de MDC current and the induced charge could be detected simultaneously and independently. This simplifies considerably charge measurements and will be helpful in the study of monolayers, e.g., the determination of the dipole moment.