Graphical interfaces for monitoring ladder logic programs

A method of monitoring a ladder logic program executing in a programmable logic controller, comprising the steps of:

• (a) displaying the graphical object on a monitor attached to the computer to depict a plant process controlled by the programmable logic controller, the graphical object being electronically associated with an element of the ladder logic program, wherein the graphical object is one selected from a group comprising Bargraph objects, Numeric objects, Trend objects, and State Change objects;
• (b) initializing a polling interval on the computer for the graphical object, the polling interval indicating a waiting period before a value for the associated element is to be retrieved from the programmable logic controller;
• (c) 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;
• (d) responding to the value 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;
• and
• (e) responding to an entry of a hot-key command by an operator of the computer by accessing a "hot-key" data structure in the computer and extracting therefrom an electronically stored filename which identifies a location on the computer where a copy of the ladder logic program is stored, and displaying the copy of the ladder logic program on the monitor at a specific rung thereof.

A computer-based apparatus for monitoring a ladder logic program executing in a programmable logic controller, comprising:

• (a) a computer, coupled to the programmable logic controller, having a monitor attached thereto, the computer further comprising:
• (1) means for drawing a graphical object on the monitor 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;
• (2) means for electronically associating the graphical object to an element of the ladder logic program;
• (3) means for 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;
• (4) means for 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;
• (5) means for 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
• (6) means for 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.

An apparatus for monitoring a ladder logic program executing in a programmable logic controller, comprising:

• (a) a computer, coupled to the programmable logic controller, having a monitor attached thereto, the computer further comprising:
• (1) means for displaying a graphical object on the monitor to depict a plant process controlled by the programmable logic controller, the graphical object being electronically associated with an element of the ladder logic program, wherein the graphical object is selected from a group comprising Bargraph objects, Numeric objects, Trend objects, and State Change objects;
• (2) means for initializing a polling interval on the computer for the graphical object, the polling interval indicating a waiting period before a value for the associated element is to be retrieved from the programmable logic controller;
• (3) means for 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;
• (4) means for responding to the value 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 for the associated element;
• and
• (5) means for responding to an entry of a hot-key command by an operator of the computer by accessing a "hot-key" data structure in the computer and extracting therefrom an electronically stored filename which identifies a location on the computer where a copy of the ladder logic program is stored, and displaying the copy of the ladder logic program on the monitor at a specific rung thereof.