1 - Electrostatic Measurements

Abstract

This chapter describes measurement techniques that are used for the detection of electrostatic phenomena in multiphase systems. The chapter also includes various transducers, probes, sensors, and instruments and emphasizes on solids-gas systems. The chapter also discusses both invasive (probes) and noninvasive (coils outside ducts) measurement techniques. The fundamental electrical quantities of measurement are electrostatic charge, current, voltage, and particle force resulting from the separation of charge. These quantities are either measured directly by a suitable detector transducer or inferred through the measurement of a related quantity, such as capacitance or resistance. The fundamental measurements of dielectric constant and resistivity in multiphase systems follow directly from methods used for solid systems. The material resistivity (or electrical conductivity) together with the permittivity are useful parameters for calculating the charge relaxation time of the material. Capacitance probes can be used with flowing suspensions as well as in fluidized beds to evaluate voidage and particle concentration through the relationship between voidage, particle volume, and concentration. Contacting electrometers are electrostatic devices with a high input resistance and come in two basic designs—high voltage capacitance based input and low voltage low current solid state input. An established method in tomography is that of Magnetic Resonance Imaging (MRI) in which a magnetic field is used to detect and visualize a multiphase system. A recent development is electrical tomography utilizing capacitance, resistance, inductance or triboelectric sensing. It is mentioned that the presence of particulate matter can have a profound effect on electrostatic discharge especially were matters of safety and explosion hazard are concerned.