Particulate matter sensor

A particulate matter sensor for sensing particulate matter present in exhaust gasses flowing from an upstream end to a downstream end of an exhaust conduit for an internal combustion engine, said particulate matter sensor comprising:

• a sensing element with a first electrode and a second electrode, said first electrode and said second electrode being configured to extend into said exhaust conduit and further configured to provide a signal indicative of an amount of particulate matter collected thereon;
• an inner shield extending along an axis from an inner shield first end to an inner shield second end, said inner shield having an inner shield wall which circumferentially surrounds said axis, thereby defining an inner shield chamber therewithin such that said first electrode and said second electrode are located within said inner shield chamber, said inner shield also having an inner shield inlet which is proximal to said inner shield first end and which passes through said inner shield wall in a direction which is traverse to said axis, said inner shield also having and an inner shield outlet which is distal from said inner shield first end;
• and
• an outer shield extending along said axis, said outer shield having an outer shield wall which circumferentially surrounds said axis, thereby defining an outer shield chamber therewithin such that said inner shield is located within said outer shield chamber and such that exhaust gases are supplied to said inner shield inlet from said outer shield chamber, said outer shield wall having an outer shield wall inlet portion which is traverse to said axis and which includes an outer shield inlet extending therethrough;
• wherein said inner shield wall includes an inner shield wall upper portion surrounding said axis and an inner shield wall lower portion surrounding said axis, said inner shield wall upper portion extending from said inner shield first end toward said inner shield wall lower portion such that said inner shield wall upper portion has an inner shield first outside diameter, and said inner shield wall lower portion extending away from said inner shield wall upper portion toward said inner shield second end such that said inner shield wall lower portion has an inner shield second outside diameter which is less than said inner shield first outside diameter;
• wherein said inner shield inlet extends radially through said inner shield wall upper portion;
• and
• wherein said first electrode and said second electrode are circumferentially surrounded by said inner shield wall lower portion.