mixer example Step7

Hi, I working on a little complicated mixer example. Process is as follows.
Process consists of mixing water and detergent like it is shown on process.pdf. My logic and ladder diagram is in second pdf doc.
I made some simplification in order to make it make it work and then hopefully I'll be abel to do a more complicated things.
When user press start system goes to run mode.
valve for water and steam is open until water reches high level and temperature is reached respectly. After that detergent is added in duration of 3 sec. Mixer is mixing water and detergent until preset temperature is reached. After that pulp1 valve is open and pump1 pulls mix of water and detergent out of tank.
After that process is completed and can be repeated when user press start again.
Basic problem is that I need some indication that process is finished. So I use Pump1_finished. But when it is 1 at the end of a cycle pump_finished is 1 and I need to reset somehow so next press on start will activate the whole cycle again. Maybe I need mor merker (M) variables, I don't know I just don't have experience.
Please help me if you are able to.
Thank you very much

This is a perfect application for S7 Graph.
Are you using Step 7 Professional??

No, I have a trial version of Step7, don't know anything about S7 graph. I'm thinking to add more merker variables to indicate when certian acton is fished, for instance to indicate that tank filling is finished and similar, but I0ll wat a little longer to see if you have any advices...

I'm trying to clearly define problem:

1.If tank is empty (sensor LL) and drain valve is not open then open valve for water.
valve for water is open until high level is reached (sensor LH)
(I assume it is better LH sensor is active while high level is not reached, and LL sensor is active when low level is reached, because of safety reasons)and valve drain is not open.
2. If actual temperature is below preset(temp sensor) and drain value is not open then open valve for steam.
3. After water level is reached (LH) then open valve for detergent for 3 sec.
4. When adding detergent is finished and not desred temperature start mixer until preset temperature is reached.
When desired temperature is reached (temperat. sensor) (I assume it is better temp sensor to be active when desired temp is not reached) open pulmp valve and start pump1 until lowlevel is reached (LL sensor).
5. When low level is reached then shut down pump1 and pump valve.
6. When start is pressed repeat whole cycle.

This sound OK, but problem is when I trz to write it in form of ladder diagram.
Please if you see problem in logic correct me.

Thanks

I tried to add positive edge (p) on last line so it pump_finish is reset after break cycle, but still no luck.
What I'm doing wrong?

Looks like you need to 'remember' that pump is finished.
You may want to remember other states as well so that your sequence doesn't restart in the middle.

--|rtv_LL|---(p)----------------+-----(pump1_finished)---
|
--| \start|--|pump1_finished|---+

when you "start" next time you drop the latching branch

or use set and reset -(S)- and -(R)-
instructions

Thanks for reply. I'll try that
Would be wise to do something like this:

  Run     Cond1    Cond2   Cond3     State

--| |------| |------| |-----|/|-------( )

 

    Cond3  State_finished

-----| |----(S)

Here when run, cond1 and cond2 is active and cond3 is not then state "State" is active. Condition that stops state is Cond3, so I signal state is finished whn Cond3 is active. At the end of a ladder diagram all "state_finished" indicators will be set. When to reset them?

when state finished is at the end of the program i would say when you press startbutton to start the program.
even if you do that the first time it doesn't matter cause the plc wont do anything with it. so i would place an alternative branche behind "start" with only the reset output

Because this question becomes more about how to control program flow, I simlified problem and manage to do something like this. It appears to do the right thing, but I manage to make it work in 100th iteration and I suspect there is a much easier way to do it. Maybe there is some rule according which I can solve this but I don't know.
Here's what I did.
Please evaluate it...

it seems to work fine but if you want it automaticly go further after stop is given.

in second nework you set run. and you don reset it anywhere. i would say set run in the first network together with the resets of st1_finished and st2_finished and make a network where youre stop conditions reset run for the rest i think you have a nice program

I'm afraid I didn't understand you well. You're right I didn't reset run explicitely, I thought when st2_finish becomes active in first network it will reset run, but maybe I'm wrong. Do you suggest to switch first and second network or maybe suggest to delete second network and to use something like this

 

start           stop st2_finish     run

|--| |----|----|/|----|/|--------|--( )

|         |                      |   st1_finish

|--| |----|                      |--(R)

                                 |--(R)

                                    st2_finish

I'll try that


I've just checked this and not working. Could you explain a little bit further what you mean?

i thought of smething like this

I did it thaks to you walters. from now on i'll use this whenever I can.
Thank you, this board rules.

Here's how I did it.

yes that is the way tht i should do it but maybe a guru like s7-guy or someone like that have a mutch better solution

Well, I'm learning about PLC for about a month but last 7 days a little more intensive since my school bought step7 v5.3 I must say it's a little hard but I0m willing to success and hope you'll help me to learn.
Thanks for everything