Patent ID: 7243539

Claim:
A level measuring apparatus using electromagnetic waves for measuring the level of the material in a container, the material in the container defining a surface, the apparatus comprising: a two-wire process control loop which supplies a current signal variable between 4 to 20 ma for measuring the level of the material in the container; an electromagnetic wave antenna extending into the container; a low power level sensor located above the surface of the material for generating electromagnetic waves, for transmitting electromagnetic waves through said antenna toward the surface of the material and for receiving electromagnetic waves reflected from the surface of the material; a low power measuring circuit coupled to said low power level sensor for determining useful electromagnetic waves reflected from the surface of the material, determining the level of the material based upon the useful electromagnetic waves reflected from the surface of the material, and transmitting a level signal representing the level of the material over said two-wire process control loop; and a power supply coupled to said two-wire process control loop for providing the sole source of power for said low power level sensor and said low power measuring circuit.