Sensor indicating presence of liq. in non-conducting tube - has high frequency source and threshold circuit with plate of one capacitor surrounding tube at measurement position

摘要

The sensor detects the presence or absence of a liquid at a given point in an electrically non-conducting tube, from outside the tube i.e. without being inserted into the fluid. The tube may be part of a thermometer or monometer. The sensor consists of a high frequency source with two capacitors. - At least one plate of the first capacitor (C2) envelopes the tube at the measurement point and is connected to the junction of diode (D2) and resistance (R2). A plate of the second capacitor (C1) is connected between an opposite polarity diode (D1) and second resistor (R1). The free diode connections are supplied from the source