Real-time soot measurement in a diesel particulate filter

An apparatus for sensing, comprising:

• a filter for filtering particulate matter from a gaseous stream, said filter having filtering media and a flowpath for the gaseous stream through the media;
• a first electrically conductive plate in electrical communication with a first lead;
• a second electrically conductive plate in electrical communication with a second lead, said first plate and the first lead being electrically isolated from said second plate and the second lead, said first plate and said second plate being spaced apart from each other with a first portion of the media and the flowpath being between said first plate and said second plate;
• a third electrically conductive plate in electrical communication with a third lead, said third plate and the third lead being electrically isolated from said first plate and said second lead, said first plate and said third plate being spaced apart from each other with a second portion of the media and the flowpath being between said first plate and said third plate, the first portion being different than the second portion, wherein said second lead and said third lead share a common electrical connection;
• and
• a source of alternating voltage, said source providing an alternating voltage to said first lead relative to the common connection.

An apparatus for sensing, comprising:

• a filter for filtering particulate matter from a gaseous stream, said filter having filtering media and a flowpath for the gaseous stream through the media, wherein said filtering media has a generally circular cross section;
• a first electrically conductive plate in electrical communication with a first lead;
• a second electrically conductive plate in electrical communication with a second lead, said first plate and the first lead being electrically isolated from said second plate and the second lead, said first plate and said second plate being spaced apart from each other with a first portion of the media and the flowpath being between said first plate and said second plate;
• and
• a third electrically conductive plate in electrical communication with a third lead, said third plate and the third lead being electrically isolated from said first plate and said second lead, said first plate and said third plate being spaced apart from each other with a second portion of the media and the flowpath being between said first plate and said third plate, the first portion being different than the second portion, wherein said first, second, and third plates are circumferentially spaced apart from each other.

A method for sensing, comprising:

• providing a filter having a flowpath therethrough and a media for trapping material in the flowpath;
• providing a first capacitor having a pair of spaced apart plates and a first portion of the media and flowpath therebetween;
• providing a second capacitor having a pair of spaced apart plates and a second portion of the media and flowpath therebetween, the second portion being different than the first portion;
• measuring a first capacitance with the first capacitor, the first capacitance corresponding at least in part to the amount of material trapped in the first portion of the media;
• and
• measuring a second capacitance with the second capacitor, the second capacitance corresponding at least in part to the amount of material trapped in a second portion of the media.

A method for sensing, comprising:

• providing a filter having a flowpath therethrough and a porous media for trapping material in the flowpath;
• placing a spatially distributed plurality of capacitive plates around the flowpath, such that different portions of the porous media and trapped material act as dielectric material between different pairs of the plates;
• sequentially applying an alternating voltage across different pairs of plates;
• measuring the capacitance of each of the pairs of plate during said applying;
• and
• preparing a dataset corresponding to the distributed capacitance of the filter.