A two conductor flexible or rigid sensor is suspended vertically in the vessel, extending its full length. A high frequency electrical signal is transmitted downward into the sensor, towards the surface of the product. A portion of the signal's energy is echoed at the material surface due to the abrupt impedance change at that point. Detector circuitry at the top of the tank measures the phase difference between the transmitted and echoed signals. The phase difference is a function of the distance traveled by the signal and is used to determine the level in the tank.
Phase Tracker benefits, as does radar, from the fixed velocity of electromagnetic signals which are not effected by the environment in the vessel. Phase Tracker, however, employs a unique, patented method of extracting the time of flight rather than measuring the actual time delay. This method has proven highly effective in level control. Unlike radar, Phase Tracker avoids the complexity of resolving the extremely short sub-nanosecond time intervals required to generate useful level information with a signal traveling at the speed of light. A steady state low energy signal, at a frequency considerably lower than radar, is transmitted into the sensor. By slowly varying the signal frequency and simply observing the voltage variations at the input to the sensor caused by the simultaneous presence of the input and echoed signals, it is possible to get a very informative view into the vessel.
