Detecting risk of icing for motor vehicle - using NTC resistor connected to bridge circuit including Zener diode

摘要

The detector for use in a motor vehicle to sense the risk of icing has a precise threshold value with a low temperature coefficient. This is obtained from an electronic circuit which provides an audible or visual alarm. The measuring circuit (CTN) comprises a negative temp. coefficient resistor in a bath and connected into a bridge circuit. This is coupled to a threshold level measuring circuit comprising a transistor (1) with a variable resistor and a second transistor (2) protected by a zener diode (8.2V) stabilising circuit. A switching transistor (3) provides an alarm signal.