Quadrature differential charge commutation sensor enabling wide bandwith field mills and other electrostatic field measuring devices

A wide bandwidth apparatus for measuring electrostatic fields, comprising:

• a first set of one or more conducting sensor segments electrically connected together;
• a second set of one or more conducting sensor segments electrically connected together;
• a third set of one or more conducting sensor segments electrically connected together;
• a fourth set of one or more conducting sensor segments electrically connected together;
• a non-conducting member for supporting and electrically insulating said first, second, third, and fourth sets of conducting sensor segments from each other and from a surrounding structure;
• means for alternately exposing and shielding said first, second, third, and fourth sets of conducting sensor segments to and from an electrostatic field to be measured that is substantially perpendicular to a surface containing said first, second, third, and fourth sets of conducting sensor segments, said means for alternately exposing and shielding said first, second, third, and fourth sets of conducting sensor segments being operative for producing a first sensor signal from said first set of one or more sensor segments and for producing a second sensor signal from said second set of one or more sensor segments, said first and second sensor signals being alternating signals that are substantially 180 electrical degrees out of phase and that represent a first differential pair signal, said means for alternately exposing and shielding said first, second, third, and fourth sets of conducting sensor segments being operative for producing a third sensor signal from said third set of one or more sensor segments and for producing a fourth sensor signal from said fourth set of one or more sensor segments, said third and fourth sensor signals being alternating signals that are substantially 180 electrical degrees out of phase and that represent a second differential pair signal;
• four transimpedance amplifiers for receiving said first, second, third, and fourth sensor signals and for producing four voltage signals proportional to said first, second, third, and fourth sensor signals, respectively;
• two AC differential amplifiers connected to said four transimpedance amplifiers for receiving pairs of said four voltage signals and for differentially amplifying an AC component of each of said pairs of said four voltage signals for producing first and second differential pair signals;
• a demodulator connected to said AC differential amplifiers for receiving said first and second differential pair signals therefrom;
• an encoder disk containing a predetermined timing pattern;
• a grounded shield for alternately shielding and exposing said first, second, third, and fourth sets of sensor segments from said electrostatic field to be measured;
• a motor for rotating said encoder disk and said grounded shield in concert;
• an encoder sensor for reading the timing pattern of said encoder disk during rotation thereof and for providing one or more timing signals;
• a timing signal processor connected to said encoder sensor for receiving and conditioning said one or more timing signals to provide one or more conditioned timing signals;
• said demodulator being operative for generating a differential output signal comprising a selected one of an inverted and non-inverted one of said first and second differential pair signals, the selection being a function of said conditioned timing signals;
• and
• a sensor assembly transmission interface connected to receive said differential output signal from said demodulator.