Hair-care appliance with hair-moistness measurement by measuring the resistance of the hair, and circuit for converting the resistance value of a resistor into a measurement signal

摘要

A hair-care appliance measures the moistness of the hair by measuring the resistance (Rx) of the hair between measurement electrodes (14A/14B). The hair resistance (Rx) is included in a T network comprising a first resistor (20) driven by a voltage source (28) and a second resistor (24). The signal current (Is) through the second resistor is measured and converted into a measurement signal (MS) by a converter (30). As a result of the use of the T network a comparatively large resistance variation of the hair resistance (Rx) is required for a given amplitude variation in the signal current (Is). This allows measurements over a wider resistance range while the resolution is maintained.