Patent ID: 6545603
Filing Date: 2003-04-08
Classification: G01D,G01F

Abstract:
Measuring device employing indirect measurement of permittivity and including two electrically conductive bodies respectively constituting a measuring probe (100) and a reference probe (200), electrical power supply means (300) adapted to deliver a DC electrical voltage of controlled amplitude, an integrator stage (500) including a capacitor switching system (530) and control means (400) adapted to define a cyclic series of two sequences at a controlled frequency, namely a first sequence (T1) during which the electrical power supply means (300) are connected to the measuring probe (100) to apply an electric field between the measuring probe (100) and the reference probe (200) and accumulate electrical charge on the measuring probe (100) and a second sequence (T2) during which the electrical power supply means (300) are disconnected from the measuring probe (100) which is connected to a summation point of the integrator stage (500) to transfer its charge into the integrator stage (500) and obtain at the output thereof a signal representative of the permittivity between the measuring probe (100) and the reference probe (200), characterized in that the integrator stage (500) includes an operational amplifier (510), a first integrator capacitor (520) constituting a feedback capacitor of said amplifier (510) and a second capacitor (530) switched between the output and the input of the operational amplifier (510) at the timing rate of the sequences (T1, T2) controlled by the control means (400), so that under steady state conditions there is obtained at the output of the operational amplifier (510) an â€œequilibriumâ€  voltage VS equal to âˆ’EÂ·Cs/C530 where âˆ’E is the amplitude of the voltage at the terminals of the electrical power supply means (300), Cs is value of the capacitor defined between the measuring probe (100) and the reference probe and C530 is the value of the second switched capacitor (530).