This invention relates to the electrical measurement art, and more particularly to a new and improved apparatus for detection and measurement of electrostatic quantities such as electrostatic fields, electrostatic voltages or electrostatic charges.
One area of use of the present invention is in non-contacting electrostatic voltmeters, although the principles of the present invention can be variously applied. Prior art techniques using an electrostatic modulator, a sensitive electrode detector surface, and an ultra high impedance preamplifier together with associated circuitry have been employed to produce non-contacting electrostatic instruments and systems such as electrostatic voltmeters, fieldmeters, coulometers, and charge control systems. Instruments using these prior art techniques suffer from major disadvantages particularly when removed from the laboratory environment and used in production or field applications. In addition, for production applications, where increased speed of response of the electrostatic instrument is desired, together with low cost and high reliability, instruments using the prior art techniques are not effective. In a hostile environment such as where the relative humidity is above 85% and contaminates such as dust, gases, and chemicals are present in the air, most prior art electrostatic instruments cannot operate effectively, and those that do require the use of extensive, high-cost driven shield guarding systems at the detector, electrostatic probe purging systems, and other local environment control in the detector area. In addition, to decrease the acquisition time of production line data, increased electrostatic instrument bandwidth is required. However, prior art techniques cannot deliver higher bandwidths without trading off decreased accuracy, increased noise, and further degradation of instrument performance due to environmental conditions.
It would, therefore, be highly desirable to provide an electrostatic detector which eliminates the foregoing disadvantages of prior art apparatus and which is superior in performance because of non-susceptibility to moisture, dust, chemicals, and other contamination, because of high reliability due to low electrical power consumption and low component count, because of non-critical construction features due to the elimination of driven shields and bootstrapping systems at the detector, because of capability of operation at higher modulation frequencies without performance degradation in other performance areas, and because of high temperature stability performance.