US Patent 9201031 Cloud ice detector

A system for detecting the presence of ice crystals in a cloud comprising two thin walled semicylinder-shaped sensors, one having a concave inner surface and oriented longitudinally in a leading edge of an airfoil and the other having a convex outer surface being oriented longitudinally in the leading edge of the airfoil so that cloud water flows towards and into contact with the convex outer surface; a temperature controlling arrangement for heating the two sensors and maintaining them at a substantially constant temperature; and a comparison arrangement for finding a difference between (i) a power to maintain the temperature of the first sensor at its substantially constant temperature (ii) a power to maintain the temperature of the second sensor at its substantially constant temperature; and comparing the difference of the powers to a threshold value for evidencing the presence or predetermined amount of ice in the cloud water.