Capacitive Sensor Used for Inspecting Fill Level in Beverage Package

A non-contact capacitive sensor is designed.It can inspect fill level in beverage package,such as beer.The electrodes of the sensor are coupled to the neck of the bottle through an air gap.Because the dielectric constant of water is much more than air,glass or plastic,the electrodes' capacitance is determined by the fill level in bottle.In the measurement circuit of sensor,a crystal oscillator is used as a steady signal source.A Gilbert balanced mixer is used to amplify the signal and lower the frequency.A DC voltage is received,after the signal is commutated and filtered.It changes with the fill level.The sensor is connected with C8051F021 singlechip.This automatic system can inspect the fill level rapidly.Its accuracy is ±1 mm.