Patent ID: 7508187

Claim:
A device for measuring an external electrostatic field, device comprising: a first conductive element ( 1 ); an amplifier ( 2 ) with an input ( 2 a ) connected to the first conductive element ( 1 ) to receive an input signal (Ve) in said input ( 2 a ), said signal being indicative of the field voltage of an electrostatic field to which the first conductive element ( 1 ) is exposed, the amplifier ( 2 ) being configured as charge amplifier so that it produces, at one output ( 2 b ) of the amplifier ( 2 ), an output signal (Vs) with a value which corresponds to the value of the input signal (Ve) integrated over time; an electronic control device ( 3 ) which has an input ( 3 a ) connected to the output ( 2 b ) of the amplifier ( 2 ), to receive said output signal (Vs); a second conductive element ( 4 ) located near to the first conductive element ( 1 ); the electronic control device having an output ( 3 b ) connected to said second conductive element ( 4 ) in order to apply a compensating voltage (Vc) to said second conductive element ( 4 ), to establish a compensating electrostatic field that affects the first conductive element ( 1 ); the electronic control device further comprising: means ( 31 ) to detect the output signal (Vs) of the amplifier; means ( 32 ) for measuring a variation in time of said output signal (Vs) of the amplifier at regular time intervals; means ( 33 ) to generate and apply periodically to the output ( 3 b ) of the electronic control device ( 3 ), the compensating voltage (Vc) with an equivalent value and with opposite polarity to the variation with time detected in the output signal (Vs) of the amplifier ( 2 ), with the condition that if said variation with time is greater than a maximum value (Vcmax), the value of the compensating voltage will be equal to said maximum value (Vcmax).