Patents by Inventor Fred C. Butler

Fred C. Butler has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Differential microampere current sensor
    Patent number: 3996513
    Abstract: Ultrasensitive current sensor detects unbalanced current in two or more AC load conductors passing therethrough. Coaxial conductors are surrounded by search sensor coil, the signal from which is amplified.
    Type: Grant
    Filed: April 24, 1975
    Date of Patent: December 7, 1976
    Inventor: Fred C. Butler