The invention relates to a sensor unit for an apparatus for preventing condensation of a gas, particularly water vapour, on a surface of an object, with a temperature measuring device for measuring an object temperature, with a dew point determination device for determining a dew point temperature of the gas in an atmosphere surrounding the object and with a regulating and control device operatively connected to the temperature measuring device and the dew point determination device and with which an adjusting device for increasing a temperature difference between the object temperature and the dew point temperature is controllable as a function of the data obtained by the temperature measuring device and the dew point determination device in such a way that a lowering of the object temperature to or below the dew point temperature is prevented. The sensor unit is inventively characterized in that the dew point determination device is constructed as a dew point sensor for the direct measurement of the dew point and the temperature measuring device is constructed as a temperature sensor operating in contactless manner. The invention also relates to an apparatus and a method for preventing condensation of a gas, particularly water vapour, on a surface of an object.