Run times: interaction between PLC program and graphic pages
The page display process is run in the System/HMI time. This means that a limited run time is available for page management. The PLC run time must not be influenced by the graphic part or page operations.The machine control logic (PLC) is run with the highest system priorities, with the sole exception of the BACKGROUND task. Operations that concern plant safety must not be run within the pages.The visual components are controlled with a low priority and are run within the System/HMI time. The more System/HMI time is made available, the more efficient the generation of images and the page change will be.
Above is an example of time (real) distribution of the various system tasks; below is a brief representation which brings together the running of the PLC tasks with higher priority, with an example of the typical System/HMI tasks and the running of the PLC task with the lower priority, to highlight the placement of the System/HMI tasks in the overall system running order.
The running speed, for example the generation of an image on a page change, can depend on the following factors:Processor performanceThis is determined by the type of HW used, which must be selected correctly.Number and types of graphic checks used.Complex checks (trend, alarm, panel, images, etc.) can require many resources to operate.A value of GPV_TEREC_xxx higher than the period configured does not cause the stoppage of the PLC program, but graphic page management may be slowed down or the control sequence response times may be extended.
Above is an example of time (real) distribution of the various system tasks; below is a brief representation which brings together the running of the PLC tasks with higher priority, with an example of the typical System/HMI tasks and the running of the PLC task with the lower priority, to highlight the placement of the System/HMI tasks in the overall system running order.
The running speed, for example the generation of an image on a page change, can depend on the following factors:Processor performanceThis is determined by the type of HW used, which must be selected correctly.Number and types of graphic checks used.Complex checks (trend, alarm, panel, images, etc.) can require many resources to operate.A value of GPV_TEREC_xxx higher than the period configured does not cause the stoppage of the PLC program, but graphic page management may be slowed down or the control sequence response times may be extended.