A measurement apparatus for alternating currents and voltages of a physical plasma ignited by applying an alternating high voltage from an alternating high voltage source to a plasma electrode via a high voltage line comprises a current transformer having a measurement winding on a ring core and a cable guide guiding the high voltage line through the ring core. A first measurement alternating voltage dropping over a measurement resistor connected between ends of the measurement winding is a first strictly monotonic increasing function of an amperage of the alternating currents flowing through the high voltage line. A second measurement voltage dropping over a measurement capacitance connected between a center tap of the measurement winding and a reference potential connector is a second strictly monotonic increasing function of an amplitude of the alternating high voltage applied to the plasma electrode with respect to a reference potential at the reference potential connector.