The humidity annex switch of type AFS-G3 serves to monitor condensed water formation. The hygro module of the measuring instrument is arranged on an aluminium baseplate so that the measuring element is near the mounting plate. Protected by the housing relative humidity near the dew point can form inside. The aluminium baseplate is adjacent to the cooling tube and conducts heat from the measuring element. The measuring point can be set inside. The threshold should be adapted for local conditions. The microswitch switches a potential-free changeover contact. The AFS requires no supply voltage. Application examples Monitoring condensed water formation: neral cooled surfaces fice and computer rooms ilding management systems oling roofs oling systems Dimensions