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

A parallel-plate capacitance-based sensor configuration which can be used to measure low mass concentrations down to a few tens of g/m³ for gas-particle systems and to study the influence of the particle characteristics such as particle size, packing or agglomeration on the effective permittivity of the mixture was developed. In this sensor a two channel symmetric structure and an AC bridge circuit were adopted to minimise the influence from the surrounding factors such as temperature, pressure and humidity. The inner diameter of the flow pipeline is 18 mm, the dimension of the capacitance plate is 100 mmx50 mm and the distance of the two plates is 10 mm. To measure the concentration of particles an in situ two-step measurement was proposed, i.e. zero point and loading measurements. Emphasis was made on estimation of the static and dynamic performance of the capacitance sensor and configuration. The baseline drift of the sensor and the influence of surrounding factors were studied. Dynamic experiments show a relative measurement error of 8% in the range from 10 to 300 g/m³. Static experiments for locally packed particle-gas systems show that the response of the sensor depends not only on particle material but also on particle size. (C) 2000 Elsevier Science Ltd. All rights reserved.