| 摘要 |
A system for measuring the level of material (16) in a vessel (14) includes a transmission line probe (12) having first and second conductors (18, 20) adapted to be positioned for contact with material in the vessel. Electronics (22) are coupled to the transmission line probe for launching microwave radiation along the probe conductors simultaneously and 180 DEG out of phase, such that portions of such radiation are reflected from the impedance discontinuity at the air/material interface within the vessel. A differential amplifier (34) subtracts the return signals at one probe conductor from the return signals at the other conductor so as to cancel noise received from the probe conductor while enhancing the strength of return signals from the material interface. Gain of the differential amplifier is controlled as a function of the apparent distance to the material surface, and level of the air/material interface is determined employing time domain reflectometry techniques. |
