Pausing a subroutine in RSLogix?

As a safety precaution I have decided that my software should have an emergency stop function that temporarily switches on/off all necessary inputs and outputs to prevent any further malfunctions. However I would like this to be only a temporary 'pause' on the subroutine so that when the fault is corrected it can return to the subroutine as if nothing had happened - all timers returning to the accumulation they were paused on, and all outputs returning to the same state they were on previously.

Thanks in advance!

To keep timer acc values you will need to use retentive timers.
You could put an xic 'safety ok' in each output rung, along with your sequence running bit.
This way when it becomes true again the outputs that were on will come back on.
The values of inputs don't need to be changed as these rely on the state of device in the field, you choose what to do with that information in your program.

This is not any kind of 'emergency stop' though, you should use a properly rated safety relay, but you can use the status of that device to pause your plc sequence etc.

Barneel,

just my opinion, aren't you violating the european directives that govern machinery?

what about risk accessment?

while it it true you can pause a machine, how will you tell others that the machine is paused?
how will you prevent maintenance from tripping a sensor and causing the machine to do part of a cycle?

regards,
james

Returning a subroutine (that is for a multi-step process) to its previous state may not be easy. It depends on how the subroutines are set up. If step relays are used, then the current step can be saved in a retentive memory location, so that if there is an emergency stop, the process step number can later be recovered (for the next startup with all safety procedures operating).

To get valid help, I think you will have to provide a copy of your subroutine, or at least more details about the subroutine structure.

two things:
emergency stop needs to be hardwired or done with safety units.
and yes you may detect pressing the stop.
as you can see the elapsed time of timers store them when stop pressed.
this way you can also adjust times when getting back.

We use the rockwell phase manager to control 'pausing/interupting' sequences/routines.
If a 'pause condition' occurs run the holding logic, save anything that needs saving. on 'resume condition' run the restarting logic, load any saved values back in.

Definately agree with others about safety being hard wored though.

IMHO, suspending the call to the subroutine that is controlling the outputs can be troublesome.

I much prefer that all of the sequence control "logic" is scanned all of the time.

If I had to make sure that all the outputs are driven "false" by some condition (e.g. emergency stop) there are a couple of ways to do this....

1. Place all of your output rungs inside an MCR zone.

2. Disable all your outputs with a single bit on each rung.

Of course the second method is more expensive in terms of memory used and execution speed, but I prefer it to the much-hated MCR zone scenario. At least you can see what is preventing the output from turning on in case 2, whereas the MCR can leave you guessing whether the MCR is "activated" or not.

Also I do not think it healthy that a machine restarts when the e-stop is reset, this should be an operator action from the panel, HMI, or SCADA.

Thanks for all of your help! I've learnt a lot!