Sensor arrangement for characterizing plasma coating and plasma etching processes in a plasma system, comprising a quartz crystal with a front electrode and a back electrode, characterized in that - the front electrode of the quartz crystal exposed to the plasma etching or plasma coating process is insulated against a sensor housing of the arrangement and is configured as a planar Langmuir probe and is connected to a current-voltage characteristic curve measuring device arranged outside the plasma system for measuring the Langmuir characteristic curve (I L), - a pyrometric sensor for measurement of the mean temperature (T Q) of the back electrode of the quartz crystal is arranged opposite the back electrode of the quartz crystal and - the quartz crystal with the front electrode and the pyrometric sensor form a combination sensor which is arranged in the sensor housing, which has an opening located opposite the front electrode of the quartz crystal, - a pivotable screening diaphragm is arranged outside the sensor housing between the opening thereof and the plasma source in the plasma system, - the combination sensor is configured to be movable and is connected to measurement (12, 13, 14) and evaluation units, and these are connected to a computer for data acquisition, evaluation and display, wherein the quartz crystal with a measuring unit for determining the quartz crystal frequency (f Q) and the planar Langmuir probe is connected to a measuring unit for measuring its current-voltage characteristic curve (I L) and the pyrometric sensor is connected to a measuring amplifier and - the computer determines the deposition or etching rate (R(t)), the plasma density (ne or n i), the electron temperature (T e) and the total energy input (E ein) of the plasma processes, using a measurement program from these measured quantities. - the front electrode of the quartz crystal exposed to the plasma etching or plasma coating process is insulated against a sensor housing of the arrangement and is configured as a planar Langmuir probe and is connected to a current-voltage characteristic curve measuring device arranged outside the plasma system for measuring the Langmuir characteristic curve (I L), - a pyrometric sensor for measurement of the mean temperature (T Q) of the back electrode of the quartz crystal is arranged opposite the back electrode of the quartz crystal and - the quartz crystal with the front electrode and the pyrometric sensor form a combination sensor which is arranged in the sensor housing, which has an opening located opposite the front electrode of the quartz crystal, - a pivotable screening diaphragm is arranged outside the sensor housing between the opening thereof and the plasma source in the plasma system, - the combination sensor is configured to be movable and is connected to measurement (12, 13, 14) and evaluation units, and these are connected to a computer for data acquisition, evaluation and display, wherein the quartz crystal with a measuring unit for determining the quartz crystal frequency (f Q) and the planar Langmuir probe is connected to a measuring unit for measuring its current-voltage characteristic curve (I L) and the pyrometric sensor is connected to a measuring amplifier and - the computer determines the deposition or etching rate (R(t)), the plasma density (ne or n i), the electron temperature (T e) and the total energy input (E ein) of the plasma processes, using a measurement program from these measured quantities.