Non-intrusive solids charge and mass flow measurements with an electrostatic flow probe

Abstract

An electrostatic flow probe for measurement of the electric charge, mass flow rate, volume loading, or concentration of solid particles travelling along a pneumatic transport pipe is mounted on a dielectric pipe section. The particles contact the inner wall surface of the dielectric pipe and cause it to be charged. The charging of this wall can be a serious metrological problem because of its influence on any non-contact measuring system based upon the electrostatic (inductive) flow probe which is a non-contact, non-intrusive device. The objective of this paper is to prove mathematically that there does not exist a problem of the dielectric pipe wall tribocharging from the metrological point of view when certain conditions are fulfilled. For the sake of illustration a sample measurement result obtained in a series of experiments performed with different powdered and granulated materials is shown to retain the validity of the mathematical and physical models. Also there have been carried out computer simulation and numerical analyses of an equivalent circuit of the probe and preamplifier to show the time response of the system to the charging of the dielectric pipe inner wall and its influence on the readings.