Capacitance-based concentration measurement for gas-particle system with low particles loading

A parallel-plate capacitance-based sensor configuration which can be used t o measure low mass concentrations down to a few tens of g/m(3) for gas-part icle systems and to study the influence of the particle characteristics suc h as particle size, packing or agglomeration on the effective permittivity of the mixture was developed. In this sensor a two channel symmetric struct ure and an AC bridge circuit were adopted to minimise the influence from th e surrounding factors such as temperature, pressure and humidity, The inner diameter of the flow pipeline is 18 mm, the dimension of the capacitance p late is 100 mmx50 mm and the distance of the two plates is 10 mm. To measur e the concentration of particles an in situ two-step measurement was propos ed, i.e. zero point and loading measurements. Emphasis was made on estimati on of the static and dynamic performance of the capacitance sensor and conf iguration. The baseline drift of the sensor and the influence of surrounding factors w ere studied. Dynamic experiments show a relative measurement error of 8% in the range from 10 to 300 g/m(3) Static experiments for locally packed part icle-gas systems show that the response of the sensor depends not only on p article material but also on particle size. (C) 2000 Elsevier Science Ltd. All rights reserved.