Device and method for determining concentration of vapor by means of oscillating body sensor

The invention relates to a device and to a method for determining the concentration of a vapor in a volume (2), in particular for determining or controlling the mass flow of the vapor being conveyed through the volume (2) by a carrier gas, wherein the volume (2) can be heated by means of a heating unit (8) to a temperature above the condensation temperature of the vapor, comprising a sensor (1), which supplies a sensor signal that is dependent on the concentration or partial pressure of the vapor. In order to provide a sensor for determining the vapor concentration using such a device or such a method, in particular a method for separating OLED layers, the sensor signal of which is not influenced, or at most slightly influenced, by the carrier gas, the sensor (1) according to the invention has an oscillatory body that can be brought to oscillation, the oscillation frequency of which is influenced by a mass accumulation formed on a surface of the oscillating body by the condensed vapor. The oscillating body ha