![]() ![]() Wait until the PLC sets the value of a specific tag to a "Running" status code.A chart could wait for a specific value on a tag, and then proceed after the value has met some set-point. In many cases, a chart will need to wait for some other system to finish with a task before moving on. This is similar to receiving a handshake from the PLC before moving on. Charts can freely read and interact with the rest of Ignition, so a step in a chart can read a tag, run a query, make a web services call, read a local file, or do anything that is possible from a Python script. When the second script finishes, the chart flows to the End step, and concludes the chart.Once the script finishes, the chart then flows to Start Motor 2, and calls a script that would start Motor 2.The Start Motor 1 action would then run a script to start Motor 1.The chart would Start and then move to the first motor.The work-flow would look like the following: Let us assume several motors all need to start from a single call. Performing multiple actions with a single call is easy to do with SFCs. Sequential Function Chart Architecture Examples Simple Chart A Backup Gateway will now pick up where the Master left off, or the chart can be canceled, restarted, or even set to run at a different step. Sequential Function Charts support redundant Gateway clusters and will persist over gateway failovers using the Redundancy Sync property. An SFC can be started with a simple button or it can be managed with the Vision - SFC Monitor component. Simple HMI interfaces can be developed to manage the SFC. The state of the transition can update in realtime, so a chart can pause until a user approves the chart to move on. Flow of the chart can be halted by a transition element. Doing so allows for looping logic to be built directly into the chart. They start at their begin step, and the logic of the chart typically flows from the top to the bottom, however charts are able to loop back to previous steps. Each element does something different, but they generally serve to either control the flow of the chart, or execute one or more Python scripts.Ĭharts always flow in the same way. Simple Visual interfaceĬharts elements are drag-and-drop, and work similarly to the components you are used to using in the rest of Ignition.Ĭharts are comprised of elements, and these element perform the work in a SFC. Parameters can also be passed into a chart as it starts, so multiple instances can work on separate tasks individually. They make use of both Python and Ignition's Expression language, so any number of tasks are possible from a single chart. A single SFC in Ignition can be called multiple times. SFCs are built in the Designer, and executed on the Gateway, so they run independently of any Clients. Scripts in a chart can only be invoked by the chart, so external scripts or resources will not be able to directly call the code from any of the steps. Linked processes - In cases where several processes should only be called together.Complicated multi-step processes - The nature of SFCs allows the user to visually build the work-flow of the chart, so troubleshooting is a breeze.A step will never become active out of order. When multiple processes must be completed in a specific order - Charts always execute steps sequentially.Pauses are handled by the chart, so there is no need to put threads to sleep. Situations where multiple processes need to run in parallel -The nature of a chart allows for controlled execution.SFCs can be used for many tasks, but they shine in the following conditions: When Should I Use a Sequential Function Chart? Charts can be monitored as they run visually, making troubleshooting easier than with scripting alone. Because of their inherently visual depiction, they help to illuminate logic to users, and facilitate intuitive development and refinement. SFCs are used to execute logic in ways that are more convenient to structure than with Python scripts or PLC programming alone. This language may be familiar to PLC programmers, as it is one of the languages commonly available for programming PLCs. Charts can loop around indefinitely, or execute a set number of times before ending. Sequential Function Charts are based on a graphical programming language in the IEC 61131-1 standard. Additional elements in the chart can determine where the flow of the chart will lead. A Sequential Function Chart (SFC) is a series of scripts that are defined in a single location, and then called in sequential order.
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