Created Date: November 03,2018

Created by: Dengel78

Hey folks,

I currently have a project working out in the field that isn't quite working as I'd like, and need to find a way to correct it. My plan is to add a timer in my ladder to shut off a solenoid, or stop the program entirely, if the project doesn't activate a limit switch with in a certain amount of time. How difficult is this to do? I can't seem to wrap my head around it yet. Maybe I need my coffee first....

Created Date: November 09,2018

Created by: Alexandru

Is not difficult.

for once, stop the program seems a bit radical. Makes me think of switching the plc to stop mode. Not sure if that could work, Since I don’t know if switching the plc would preserve the outputs. I guess it could work, it I wouldn’t use this way cause as I said, I find it too radical a never seen it implemented.

for second, the usual way:

first of all, I,like your idea. It can be implemented on a timed motion, a piston, or any other critical motion which needs checked before the machine advances to next step.

that kind of safety is easy to implement. Have a master control relay implemented in your program. If this relay ( a control bit) is off, the machine will hold state and motion ( advance to next step in machine cycle) is disabled.

what disables the MCR (master control relay): usually door switches, control power, or any input configuration which is not a valid state of the machine.

in your case, a failed or timed out motion could also be included in the list.

program logic: if MCR is off, then jump to a subroutine meant to reset the MCR by allowing direct access to reset any of critical switches/ control bits.

if MCR is on. Then your program should be free to run.