Patent ID: 11940314
Assignee: ROCHESTER SENSORS, LLC
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 6:
7. A method for calibrating a Time Domain Reflectometry (TDR) measurement system, the TDR measurement system comprising a housing, an elongate measurement probe for measuring material level and having coaxially located inner and outer electrodes, and an electronics assembly in said housing for transmitting a signal along the elongate measurement probe and for receiving at least a return echo upon encountering a change in the impedance with respect to the inner and outer electrodes to thereby determine the position of material determined by the elongate measurement probe, wherein a calibration trace of known length is embedded in a printed circuit board (PCB) of the housing, and wherein an end of the calibration trace is electrically joined with a beginning of the elongate measurement probe such that the calibration trace together with the inner and outer electrodes define a waveguide along which electromagnetic pulses propagate during TDR measurements, wherein the method comprises:
determining an echo profile of the calibration trace by transmitting electromagnetic pulses along the calibration trace and detecting echoes therefrom to obtain an electronic measure of the length of said calibration trace;
measuring a temperature of the calibration trace and comparing the obtained electronic measure of the length of the calibration trace with the known length to derive a temperature compensated calibration factor (Cf) of the calibration trace;
determining a system clock cycle distance calibration (Cd) using the calibration factor and the known length of the calibration trace such that the electronic length equals the known length;
measuring one or more echo times associated with one or more known lengths along the elongate measurement probe for electronically measuring probe length;
calibrate the electronically determined probe length using said system clock calibration distance and said one or more echo times;
determine an offset in distance between the calibration trace and the probe;
calculate and store the calibrated probe length based on said offset.