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About Arvest

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  1. Thanks for the reply. I still need to figure out how to get that pattern values into my PLC program, but that is (in this case) a more specific Modicon question. You are right about the Modsbus RTU being too slow. I have used Modbus in the past to provide corrections to a robot arm in real time, but that was Modbus TCP. I mixed the two up. Modbus TCP should be fast enough, depending on how effecient the PLC is at getting that signal out there. Direct connection to the PLC would not be the preferred option because of all the cabling involved. A RTU would be a much lighter and simpler option. Regarding the coils: currently we use a normal flyback diode, and this achieves a 7 ms closing time. I will investigate using a MOV or Zener in the design, but I believe not the coil, but the spring inside of the valve is the limiting factor wrt the closing time.
  2. Hello, quite new to PLC's, currently figuring out if / which PLC is the way to go for my application: I'm construction a machine with a two axis (X/Z) with 88 valves mounted on them. The X axis makes a scanning motion, and after every pass, the Z axis moves down 2.5 mm. When the X-axis moves, the valves need to switch in a certain pattern, opening / closing with a resolution of 2.5 mm, based on the current X and Z-position (i.e. encoder values). My goal is to move around 0.25m/s, so they would switch around 100 times per second (i.e. every 10ms). I want to be able to upload the pattern via Ethernet connection from my PC. The valves will most probably be switched through a Modbus RTU digital I/O unit(s) I ended up with the Modicon M241 as a nice PLC with the right I/O capabilites and features for my application. However, I don't know if it is suitable, as I am unable to find out how the whole uploading a pattern to memory, and then retrieving values one by one from memory during operation would work (i.e. which instructions should I use in my PLC program?)