Search code examples
automationplcsiemensscadaladder-logic

Issue with NC contact behavior when converting from Allen Bradley to Siemens


Image I have an issue. We're currently rewriting a program from Allen Bradley to Siemens and I've noticed something strange. How can bit B3:2 turn true if it’s blocked by an NC (Normally Closed) contact that gets activated right there? If it worked in Allen Bradley, how will it work in Siemens?

I don`t understand how it must be working


Solution

  • Old logix500 aye ;) S7-1200 and 1500 would scan the ladder you posted in the same order. So you may perform a direct port (replacing the variables as required):

    TIA portal snippet

    TIA Portal does not allow branches containing 'output-type' instructions to be joined back up, hence the open ends on the right side. But it is functionally equivalent.