Patents by Inventor David C. Littlejohn

David C. Littlejohn 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).

  • Patent number: 5416480
    Abstract: An interface circuit for use with process controllers permits analog signals to be input to a process controller through a binary interface of the process controller and permits analog signals to be output from the process controller through the binary interface. The input analog signal is converted to a digital sample of N bits. An identification pulse and the N bits of the digital sample are transmitted to the process controller at a rate selected for compatibility with the scan time of the process controller. The process controller includes a software routine for recognizing the identification pulse and the N bits of the digital sample. An equivalent approach is used for outputting analog signals through a binary interface of a process controller. The interface circuit can include multiple channels for inputting or outputting multiple analog signals.
    Type: Grant
    Filed: April 8, 1994
    Date of Patent: May 16, 1995
    Assignee: Interactive Process Controls Corp.
    Inventors: Kevin V. Roach, David C. Littlejohn, James G. Calvin