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A sensor for detecting particulate matter in an exhaust stream of an engine. The sensor may be a spark-plug-like device having an extended center electrode composed of a stainless steel or other material. The electrode may have a thin passivating layer formed on it. The layer may be grown or deposit

A sensor for detecting particulate matter in an exhaust stream of an engine. The sensor may be a spark-plug-like device having an extended center electrode composed of a stainless steel or other material. The electrode may have a thin passivating layer formed on it. The layer may be grown or deposited on the electrode within the exhaust system. The sensor may detect charge transients indicative of particulate concentration in the exhaust stream. Information about particulate matter in the exhaust system along with other engine information may be processed for controlling or adjusting parameters of the engine to affect the particulate matter in the exhaust system.

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1. A particulate matter detector comprising:a spark plug having a center electrode;a rod attached to the center electrode; anda passivation layer formed on the metal rod; andwherein:the rod is a metal rod;the metal rod is a steel rod; andthe passivation layer is oxidized steel.2. The detector of cla

1. A particulate matter detector comprising:a spark plug having a center electrode;a rod attached to the center electrode; anda passivation layer formed on the metal rod; andwherein:the rod is a metal rod;the metal rod is a steel rod; andthe passivation layer is oxidized steel.2. The detector of claim 1, wherein the steel is stainless steel.3. The detector of claim 2, wherein the steel is 304 stainless steel.4. The detector of claim 2 wherein:the metal rod has a length between 0.25 inch and 12 inches; andthe metal rod has a thickness between 1/32 inch and ⅜ inch.5. A method of making a particulate detector, comprising:obtaining a spark plug having a center electrode;attaching a metal rod to the center electrode; andforming a passivating film on the metal rod; andwherein:the metal rod comprises stainless steel; andthe passivating film is oxidized stainless steel.6. The method of claim 5, wherein the metal rod comprises 304 stainless steel.7. A method of making a sensor, comprising:forming an elongated piece of metal placing the elongated piece of metal in an insulator;forming a terminal connected to the elongated piece of metal;forming a thin film of insulation on the elongated piece of metal; andwherein:the elongated piece of metal is stainless steel; andthe film of insulation is formed by oxidizing the stainless steel.8. A detector comprising:a metal base;an insulator situated in the metal base;an elongated piece of metal situated in the insulator; andan insulative film formed on the elongated piece of metal; andwherein:the elongated piece of metal comprises stainless steel; andthe insulative film is a forming of a passivating film from the stainless steel.9. The detector of claim 8, wherein the elongated piece of metal comprises 304 stainless steel.10. The detector of claim 9, wherein:the elongated piece of metal is connected to an amplifier; andthe amplifier has an output that may indicate a concentration of particulate matter in a vicinity of the elongated piece of metal.11. The detector of claim 10, wherein the elongated piece of metal is situated in an exhaust system of an engine.12. The detector of claim 11, further comprising;a processor comprising the amplifier; anda plurality of sensors connected to the engine and the processor; andwherein the processor provides control signals to the engine for affecting an amount of particulate matter in the exhaust system.13. The detector of claim 12, wherein the control signals may affect fuel injection timing and percent of exhaust gas recirculation of the engine.14. A detector comprising:a base;a probe situated in the base; anda passivating film formed on the probe; andwherein:the passivating film is formed from a material of the probe;the probe is connected to an amplifier; andthe amplifier has an output that may indicate a magnitude of charge of a concentration of particulate matter on the film of the probe.15. The detector of claim 14, further comprising;a processor comprising the amplifier; anda plurality of sensors connected to an engine and the processor; andwherein the processor provides control signals to the engine for affecting an amount of particulate matter in an exhaust system.16. The detector of claim 15, wherein the control signals may affect fuel injection timing and percent of exhaust gas recirculation of the engine.17. A detector comprising:a supporting base; andan electrode having a detecting portion and a non-detecting portion; andwherein:the non-detecting portion is situated in the supporting base;a passivating film is formed on all of the detecting portion of the electrode; andthe electrode is for detecting particulate matter, in a vicinity of the electrode, which has a charge and attaches to the passivating film.18. The detector of claim 17, wherein:the electrode is connected to an amplifier; andthe amplifier has an output that may indicate a concentration of particulate matter in the vicinity of the electrode due to an input from the electrode of the charge of the particulate matter that attaches to the passivating layer.19. The detector of claim 18, further comprising;a processor comprising the amplifier; anda plurality of sensors connected to an engine and the processor; andwherein the processor provides control signals to the engine for affecting an amount of particulate matter in an exhaust system.20. The detector of claim 19, wherein the control signals may affect fuel injection timing and percent of exhaust gas recirculation of the engine.