Posted 9 Jan 2012 Hello everyone, I can not figure out how to know if a PLC will be fast enough for a project. I have a set of 6 valves which I need to close simultaneously (or within 0.1ms). I have synchronous clocks hooked up to each valve to let me know when the valve closed and currently I am about 3ms off (fastest to slowest). So I want to write a program where I can delay each valve as necessary (to within 0.1ms) so that they all close at the same time. Each valve is on its own digital output from the PLC with high speed relays in between. What PLC setup can you suggest (Siemens preferred) that would guarantee me control to that resolution? Would it be more like an S7-400 or a S7-1200? Is it even possible? Thanks for any help in understanding this. Simon Share this post Link to post Share on other sites
Posted 10 Jan 2012 Simon, First of all, you need to make sure the valves you are controlling are repeatable enough to allow 0.1ms coordination. Not all valves (and precious few pneumatic or hydraulic valves) are capable of this level of repeatability. Valves where a solenoid acts directly on the moving part will do it in the powered direction as long as the mechanism being moved is free enough. With those qualifiers, you might want to consider the FM352-5. I don't think there are any regular processors from any major PLC manufacturer that have any less than 0.5ms timed interrupt. The FM352-5 is a high speed boolean coprocessor that uses a FPGA for parallel processing. It is capable of some pretty fast throughput. It has been a while since I read through the manual, but I think it might work for you. HTH, Ian fm352-5_e.pdf Share this post Link to post Share on other sites
Posted 11 Jan 2012 Ianbuuckley have a good idea but I'm not sure you will be able to have this precision with a relay interface. Delay to close contact is not egal on each time the relay is energize. Share this post Link to post Share on other sites
Posted 12 Jan 2012 Thanks for the responses. The guys are fairly confident about their valves being consistent at least. Just when certain parameters are hit, I need to shut them all at the same time (within 5ms of conditions met). Since there is variability in each relay/valve, I was hoping that by delaying each valve after a averaged closing time, I could get them all to close to within 0.1ms. How does the coprocessor work? That is a new idea for me. Will it still be limited by scan time? What if I used a PC based PLC? Do those use the PC processing power? Will the fieldbus speed be a limiting factor? Right now the system uses Profibus. Thank you, Simon Share this post Link to post Share on other sites