maintenance and with some documentation they don't need any computer for basic analysis.Īccording my experience I prefer simple LAD functions according Grafcet std, what is also very easy to understand, it's faster to made and you don't need any special licence as you will need for SFC (only for Enterprise version if Rockwell doesn't changed this). For old Siemens Step7 is possible to export this flow chart to HMI, so you can share flow chart with i.e. Main reason why it's so popular is fact that (I'm not sure about US) in Europe it's quite common that you will receive documentation (flow chart - organic analysis) which completely match flow chart in program. Also in on-line mode you can find this very easy to understand, but it depends on process (if it's very fast process you will end up anyway with trending). For "not programmers" if you use SFC with very good descriptions it's very easy to understand machine functionality. Mostly it's used by French, because SFC is compatible with French programming standard called "Grafcet" (EN60848).Īccording my experience SFC is not so bad for overview only in case if you keep function in some reasonable size (number of steps and parallel branching), otherwise it becomes quite messy. Yes you are right, it's used in Europe but it's not so frequent as you may think. And CLX introduced the capability to edit the chart online, though arguably that shouldn't be necessary. The ControlLogix implementation was a long time coming, but similar to the NP PLC5. Diehards like myself started using them, but most continued to stay away. Finally, with the third attempt (5/20 /30 /40 /60) they came up with a very useful and powerful implementation. With the 5/250, you were obliged to have a master SFC - this typically ended up as a chart with one step that called a ladder file with all the logic. The second attempt with the 5/250 was a marginal advance but still too limited to be useful. Likely, many people tried it out, found it useless and just stayed away. My advice is don't try to incorporate too much in a single chart.ĪB's initial attempt at implementing SFC's was with the introduction of the PLC5 (5/15 & 5/25) and was virtually useless. I have used SFC's for bread mixers, shrink wrappers, carton machines and probably some less appropriate applications as well. Your idea to implement a state machine would be appropriate. They also aid maintenance, since it is immediately obvious where a sequence is hung up. However, with the appropriate application, they are very helpful in program organisation and reduce or even eliminate tediously long and complex rungs full of interlocks since the sequence logic is embodied in the chart. I guess the overwhelming response answers that question.įirst, they are not applicable in every situation. I'm curious how many forum members have experience with Sequential Function Charts?
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