Integrated electrostatic detection in analytical weighing

Laboratoire de Production Microtechnique (LPM), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

Abstract
Various examples of routine laboratory work show that electrostatic charges exert forces on the material to be weighed and the weighing pan, thus causing significant falsification of measurement results. Recent advances in weighing technologies allow the user to reduce these shortcomings. An integrated sensor for measuring the electrostatic forces during normal operation in an analytical balanced is presented and shown that errors over four orders of magnitude ranging from a few μg to several mg can easily be detected.

Introduction
An electronic analytical balance measures not directly a mass but the force of its weight. The uncertainty of this force depends on the technical specification of the instrument but also of many environmental effects like temperature variations, air drafts, evaporation or water adsorption of the object being weighed. In addition, the presence of electrostatic forces plays an important role in the accuracy of weighing data. Following a brief introduction to the physics of static electricity, this article describes how electrostatic charges arise and dissipate, how modern analytical balances detect their presence, and how large the measurement errors can be.

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