Hi again - I tried to wrap my head around this and I think I get some ideas here-
NOTE - I have change some things - you need to reprogram the PL and the switch channels a little
I start from the beginning. We need three basic functions. A level circuit for ATO to the main system. A level circuit for the salt mix system and a timer for the drinking water system. here is my suggestions reactions time and other things may have to be adjusted
2 sensors system for the main system. Max on-time may need to be adjusted
The one sensor system for the ATO of the salt mixing system. Observe reaction time on the sensor (red) and no maximum on-time (means that it is deactivated) (blue)
A timer - 42 minutes period will have its explanations further on
Now we need some programming
We start with the ATO for the main system. You want a backflush before it starts to fill and you want 2 minutes (120 sec) backflush. It means that you need to delay this first step with at least 125 sec.
Next step is to define the backflush for the minutes. This step is not the same as before - it is only valid for the ATO of the main system
Now it is the Drinking water turn. It is the same here 125 sec delay for the action
and a backflush before
Now to the saltwater mix station. You will fill it an after that mix and pump it over after the mixing. It is enough with on high level sensor as I said before. It will be inactive when it is filled up and during the mixings with salt. When you start to pump it will be active rather soon and in order to avoid filling with RODI water during the time it empties - a delay is handsome. You say 4 minutes - let us make the delay to 6 minutes or 360 sec
Even here -we need a 120 sec backflush. It will be the first two minutes of the six minutes delay but I think that´s not matter.
Now the basic modes ar configured - now we nhave to play boll as Franz Beckenbauer - with finesse.
As I understand - the drinking water is the most important tasks for your RODI - it is a certain time every day. It is your solenoid S3. - It is easy - my switch channel 3 will serve S3
Your ATO for the main system should not run if timer 1 is active - this is the PL for that. Note the invert function of the timer
This should be done by Solenoid S1 and we use switch channel 1 for S1
Your ATO for the Salt Mixing station should not run if your drinking water or ATO display system runs. Need a "help" PL here
Now we combine this with run of ATO for Salt mix station
Connect to a switch Channel
Now - the backflush - Solenoid 2
An help PL again
The sharp
Connecting
I have configure this on a P3 - can´t test fully out - only two level sensors. You need to test this out. Something that I do not know about is if a DT fill up or the drinking water block the ATO SMS fill up - if it will be a new 6 minutes wait period. It can also happens that it will com multiple pulses to the S2 - if it will be a real problem or not - I don not know.
I have not tested this - please test carefully before you use this
The PL rows
The Switch channels
Good luck
Sincerely Lasse