Electrical sensor for measuring capacitance change and conversion into a voltage signal

An electric sensor for measuring a capacitance change of a condenser (7) and conversion into a voltage signal (Udiff) that corresponds to the capacitance change and that is transmitted to a display or measuring device (15) and evaluated, using a transformer (1) with two bifilarly wound coils (La, Lb) on a core (2), whereby a signal generator (14) is connected to the input of the primary coil (La), especially for reporting a distance change of an object (12, 19) to be detected or to be monitored or to report the movement of two objects (12, 19) moving relative to each other, characterized by the following features:

• a) each one of the two condenser electrodes (Ea, Eb) of the condenser (7) is connected to the outputs (4, 6) of the primary (La) and secondary (Lb) coils, whereby said electrodes form an electric field (9) between them and there is a shared reference electrode (8, Ec) across from them which, for each of the condenser electrodes (Ea, Eb), additionally forms an electric stray field (10, 11), so that each condenser electrode (Ea, Eb) yields a stray field condenser (Ca, Cb) with the reference electrode (8, Ec),
• b) the input (5) of the secondary coil (Lb) is connected to a fixed system reference potential (8),
• c) on the core (2) of the transformer (1), there is a tertiary coil (Lc) to which the display or measuring device (15) is connected,
• d) an object approaching the condenser electrodes (Ea, Eb) and the reference electrode (8, Ec) brings about a change in the capacitance of the stray field condensers (Ca, Cb) relative to the reference electrode (Ec, 8), whereby this capacitance change generates a differential mode voltage (Udiff) in the tertiary coil (Lc) and this voltage is evaluated in the display or measuring device (15).