Do...While in STL ---- HOW?!

MarkoM

In FC3: !!!PROBLEM!!!
1. open lower valve(to empty filter)
2. empty filter (wait until the filter is empty)
3. (when filter is WITHOUT ANY water) start air compresor
4. when air presure is high enough open valve so air can access filter (again wait until presure is right and then open valve)
5. timer 5min
6. stop compresor, close valve, start pump to refill filter with water from tank
7. when filter's upper flow sensor is active (filter is full) stop pump and go back to OB1

Hello again MarkoM,

I still don't think you need anything like do, while or so. For that purpose, you just use the cycle time of your PLC and the variables that you use anyway for the while condition. Let me give you a simple example that ilustrate the thing, it is a bit alike your application, I believe that then it will be much more clear.

Let's have a station for pumping water. In that station you have source of the water S (a lake for example), two tanks T1 and T2 and then the outgoing pipes P that lead somewhere. They are connected in series and between each part is a valve noted as numbered V.
Let's say its like this: S]---(V1)---[T1]---(V2)---[T2]---(V3)---[P..... .

Now, you want to do following:
a) fill up T1 to full when I press a button at the control by the lake
b) once T1 is full, stop filligng it and start filling T2 from T1
c) once T2 is full, stop filling it and open up the valve to the outgoing pipes P

You can do this all pretty much all in one block with few simple instructions and without any complicated while cycles etc. and that's all thanks to the networks.

Firstly, variables that I will use:
I 1.0 - input from the control to start filling up T1 (1 = opened)
Q 1.0 / Q 2.0 / Q 3.0 - outputs signaling each of the valves V1 / V2 / V3 to be opened (1 = opened)
I 1.1 / I 2.1 - signaling inputs from each of the tanks T1 / T2 if the tank is full (1 = full)
I 2.0 - signaling input from tank T2 that it is empty (1 = empty)

Now I introduce a couple of networks in the block that will cover the handling:

[code]Network 1:
A I 1.0 // start filling up
AN I 1.1 // tank is not full
JCN _001 // conditions not met, jump
S Q 1.0 // open V1
_001: NOP 0 // end of network, do nothing[/code][code]Network 2:
A I 1.1 // tank T1 is full
JCN _002 // conditions not met, jump
R Q 1.0 // close V1
S Q 2.0 // open V2
_002: NOP 0 // end of network, do nothing[/code][code]Network 3:
A I 1.2 // tank T2 is full
JCN _003 // conditions not met, jump
R Q 2.0 // close V1
S Q 3.0 // open V2
_003: NOP 0 // end of network, do nothing[/code][code]Network 4:
A I 2.0 // tank T2 is empty
JCN _003 // conditions not met, jump
R Q 3.0 // close V3
_004: NOP 0 // end of network, do nothing[/code]Now for application as simple as this, you can literaly write it to OB1. Obviously it is better to structuralize things and if you have it as you do, you can just call a function block with respective functions for further control in order to avoid having all the text in one file. Anyway, just if you call if from somewhere, each cycle you call it, each cycle it will go through the networks and do the commands in them.

By the structure of logic only one network at the time applies (hopefully I didn't make a mistake there so it is true), but you can do it that more will be completed at the time of each cycle, it is just matter of setting up the conditions. Since the code is sweeped every cycle, it is while, even though none is programmed there, because while the conditions A I 1.0 and AN I 1.1 are both true (in network 1), it does the command S Q 1.0 so it keeps the output active and hence the device on it opened and so on.

So you see that the need for usage of while in a manner of standard programming languages is not that high, I can imagine using it maybe if you would make some algorithm, but it is always better to try avoid such thing, because it just increases the length of a cycle, which might in example cause your devices react slower than you need.

Hope this helps.

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