Method for locating the surface of a polymer particle bed

A method for determining the upper surface level of a bed of polymer particles that are contained in a vessel, said vessel having an upper section into which incoming polymer particles are introduced, said method comprising introducing into said upper section water wet polymer particles, providing a guided wave radar probe unit comprising a combined radar pulse transmitter and reflected radar pulse receiver, said guided wave radar probe unit having fixed thereto a first end of an elongate rigid radar inactive member, said radar inactive member carrying at its distal end a pair of spaced apart rigid radar active probes, said radar active probes being spaced from said radar probe unit by said radar inactive member, immersing said radar active probes at least in part into said bed of polymer particles, positioning said radar inactive member so that said incoming polymer particles impact said radar inactive member and not said radar active probes, transmitting a first radar pulse from said guided wave radar probe unit initiating at the top of said probes and proceeding along said probes into said bed of polymer particles, receiving a reflected radar pulse generated by said first radar pulse when said first radar pulse contacts said upper surface of said bed of polymer particles, and recovering said reflected radar pulse at said guided wave radar probe unit.