Abstract: A device for detecting snow and ice which has a humidity sensor and an ambient temperature sensor. An evaluator switch is controlled according to a humidity sensor-measured variable, producing a control signal at set humidity values for defrosting a surface which is being monitored for snow and ice. The ambient temperature sensor activates the humidity sensor within a temperature range of between +2° C. and −12° C. The humidity sensor itself has a PTC (positive temperature coefficient) heating element. The current consumption of the heating element is used as a measure of humidity. Both the ambient temperature sensor and the humidity sensor are positioned at a mutual distance in a longitudinally extended sensor cartridge made of plastic. The temperature sensor is thermally decoupled from the PTC heating element. The PTC heating element is built into a metal sleeve in such a way that it is corrosion and humidity proof.

Abstract: A moisture sensor with two heatable concentric moisture electrodes and a temperature sensor detecting the electrode temperature is set into the roadway surface to be monitored. The moisture electrodes are heated by a heating current circuit. The heating current circuit is connected to a computer which has a store for storing device-specific parameters, desired values and a processing program. During each measuring cycle the computer processes the temperatures of the moisture electrodes measured by the temperature sensor and a signal which is representative of the surface moisture. A control signal is produced therefrom which heats the moisture electrodes. An alarm or switching signal is produced when the moisture electrodes have reached a temperature characteristic of the formation of ice and a conductivity indicative of moisture is present between the moisture electrodes.

Abstract: The volume of water in circulation is controlled by means of a bell-type mixer (4) which has a stationary section disc (6) and a somewhat sickle-shaped rotary distributor bell (7). The section disc has at least three separate passage openings, the first of which is connected with the boiler feed pipe (KV), the second (12) with the heating pipe (HV) and the third with the boiler return pipe. The distributor bell (7) is acted upon externally by the heating return water pressure and internally housing a communication duct (19). The distributor bell shunts the boiler feed pipe over a limited area of rotation via the second passage opening (12) with the heating pipe and simultaneously frees a variable area of the opening into the second passage for the admixture of return water. In this way optimal regulation is achieved with little structural, maintenance or operational outlay.