Abstract: A method and apparatus for processing a time domain reflectometry (TDR) signal having a plurality of reflection pulses to generate a valid output result corresponding to a process variable in a vessel. The method includes the steps of establishing an initial boundary signal before the process variable is locates in the vessel, storing the initial boundary signal, detecting the TDR signal, and determining a baseline signal by subtracting the initial boundary signal from the TDR signal. The method also includes the steps of establishing a signal pattern having a time range based on the width of reflection pulses in the baseline signal, comparing the baseline signal to the signal pattern until a reflection pulse in the baseline signal matches the signal pattern, determining a maximum value of the reflection pulse that matches the signal pattern, and calculating an output result based on the maximum value.