Method and system for compensating for variation in attenuation measurements caused by changes in ambient temperature

A method for determining the attenuation of a radio frequency (RF) signal caused by a diesel particulate filter (DPF) using a system comprising an RF transmitter for generating said RF signal connected to a transmit antenna positioned on a first side of said DPF via a transmit cable, a transmit detector and receive detector for measuring the power of said RF signal before and after passing through said DPF, and a receive antenna positioned on a second side of said DPF connected to said receive detector via a receive cable, the method comprising the steps of:

• (a) disconnecting said transmit cable and said transmit antenna from said RF transmitter;
• (b) disconnecting said receive cable and said receive antenna from said receive detector;
• (c) forming a first path between said RF transmitter and said receive detector that does not include said transmit cable, said transmit antenna, said receive cable, and said receive antenna;
• (d) generating said RF signal at a first frequency;
• (e) determining the attenuation of said RF signal caused by said first path at said first frequency at a first ambient temperature based on the difference between the power of said RF signal before traveling through said first path and the power of said RF signal after traveling through said first path;
• (f) connecting said transmit antenna to said RF transmitter via said transmit cable;
• (g) connecting said receive antenna to said receive detector via said receive cable;
• (h) forming a second path between said RF transmitter and said receive detector that does include said transmit cable, said transmit antenna, said receive cable, and said receive antenna;
• (i) determining the attenuation of said RF signal caused by said second path at said first frequency at said first ambient temperature based on the difference between the power of said RF signal before traveling through said second path and the power of said RF signal after traveling through said second path;
• and
• (j) determining the attenuation of said RF signal caused by said DPF at said first frequency at said first ambient temperature by subtracting from said attenuation caused by said second path the attenuation caused by sources in said first path that are also present in said second path and the attenuation caused by said transmit cable and said receive cable.