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Graphical interfaces for monitoring ladder logic programs

  • US 5,321,829 A
  • Filed: 07/20/1990
  • Issued: 06/14/1994
  • Est. Priority Date: 07/20/1990
  • Status: Expired due to Term
First Claim
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1. A computer-based method of monitoring a ladder logic program executing in a programmable logic controller, comprising the steps of:

  • (a) drawing a graphical object on a monitor attached to a computer to depict a plant process controlled by the programmable logic controller, wherein the graphical object is selected from a group comprising Bargraph objects, Numeric objects, Trend objects, and State Change objects;

    (b) electronically associating the graphical object to an element of the ladder logic program;

    (c) setting a polling interval on the computer to indicate how often a value for the associated element is to be retrieved from the ladder logic program executing in the programmable logic controller;

    (d) specifying action parameters on the computer to indicate changes in the display of the graphical object that are to occur in response to changes in the value of the associated element;

    (e) responding to a triggering of the polling interval by transmitting a query message from the computer to the programmable logic controller requesting a value for the associated element and by resetting the polling interval; and

    (f) responding to the value for the associated element being input from the programmable logic controller to the computer by changing the display of the graphical object in accordance with a change in the value of the associated element.

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