Timer help

Hi.

hope to finde some help/ guidance here.

so i have a S7-1212

i have written a small ladder program to controll 3 watervalves

my problem i just cant get my head arround on how to controll them on a time schedule.

here is the scenario:

manual and auto mode

in auto i press start.

first we check all valves are closed.

then we check if we have a minimum pressure.

when we have pressure the timer starts and valve 1 opens.

after 20 minutes valve 1 closes again and valve 2 opens.

after 30 minutes valve 2 closes and valve 3 opens.

after 20 minutes valve 3 closes and we start all over again

valve 1 opens and so on.

any hints ??

here is the basic manual mode ladder

And the answer is a finite state machine.

Or in LAD.

make step counter

in each step do whats required when step finishes increment step counter by 1

in last step change counter back to 1 (0 = no sequence)

when sequence starts (init)

do check for pressure then force step = 1

also after failure do you need to continue sequence or start from scratch or both?

and what happens if pressure drops mid sequence?

of course step counter must be STAT or DB, NOT Temp!

I will take a look at that. Thank you Jacek :-)

Piotr.M

if i loose pressure the pump stops and i get no water.   it is up to the opperator/snowmaker to reset or do what ever they want.

i only check the pressure before start to be sure we have enough pressure to make snow and not slushice.

i will check both options   Thanks for the quick answers :-)

\\Thomas