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: An analog signal measuring apparatus has: a sampling gate circuit, having a plurality of input terminals including an analog signal input terminal and a feedback signal input terminal, for generating an output signal of high or low level when a sum of input signals goes beyond or falls below a predetermined threshold value; a signal generating circuit, connected to an output terminal of the sampling gate circuit, for changing an output signal by a predetermined level toward a direction in which an output signal level of the sampling gate circuit is inverted when a trigger signal is applied to the signal generating circuit, and for supplying a feedback signal to the feedback signal input terminal of the sampling gate circuit; and a read circuit for generating a value obtained when the feedback signal from the signal generating circuit converges, the feedback signal corresponding to a value of an analog signal supplied to the analog signal input terminal, wherein a ratio of an increment .DELTA.