plc结构化文本循环延迟

Question

I am trying to have a loop where it will start at 100 and drop until it hits to a point where the while condition no longer holds true.

I started with

While Solar_Power_House_W_Solar_PER <= OneHundred AND BatChargePercent < OneHundred DO
    State_Dis_Charge := false
    FOR PLC_SetLoopChargeValue:= 100 TO 0 By -1  DO
        ConvertoReal   := INT_TO_LREAL(PLC_SetLoopChargeValue);
        Divide         := ConvertoReal DIV(100);
        PLC_SetCharge  := Divide;         
        PLC_Charge     := 1500 * PLC_SetCharge; 
        RB_Charge      := PLC_Charge;
        Visual_RBPower := 1500 * PLC_SetCharge;    (*Charge *) 
    END_FOR;

The problem I believe I have with this is that it cycles too fast so the condition never gets out of the while loop because it takes a while for the system to update so I thought of adding a delay portion:

While Solar_Power_House_W_Solar_PER <= OneHundred AND BatChargePercent < OneHundred DO
    State_Dis_Charge := false;
    wait(IN:=not wait.Q , PT:=T#50ms);
    if Wait.Q Then 
        FOR PLC_SetLoopChargeValue:= 100 TO 0 By -1  DO
            ConvertoReal   := INT_TO_LREAL(PLC_SetLoopChargeValue);
            Divide         := ConvertoReal DIV(100);
            PLC_SetCharge  := Divide;         
            PLC_Charge     := 1500 * PLC_SetCharge; 
            RB_Charge      := PLC_Charge;
            Visual_RBPower := 1500 * PLC_SetCharge;    (*Charge *) 
        END_FOR; 
    END_IF;
END_WHILE;     

How I think it should work is every 50ms 1 for loop should run. Currently nothing happens every 50ms.

Answer 1

You have to consider that WHILE and FOR are executed synchronously. It means blocking. It means that interpreter do not execute next line, until previous line is finished.

1. This means that "running to fast" cannot apply here. It does not matter how fast it runs, the execution of the lines will be always in order.

2. The only thing I would change and loop not from 100 to 0 but vice versa from 0 to 100, because I am not sure this backward will work fine. And then all you have to change:

    ConvertoReal := INT_TO_LREAL(100 - PLC_SetLoopChargeValue); 

3. You do now show all code it is VERY HARD to judge but if FOR loom is complete it totally make no sense. You calculate some variables but you do not use them there. You know that you cannot use them outside of your FOR loop, right? Because outside of your FOR loop those variable will be always same value of last loop.

4. In your second example your FOR loop, although it might work, you should not use timer to run the loop inside the loop. Because loops are synchronous and times async.

5. As I understand you task you do not need WHILE at all. With this approach your program execution of other parts will be blocked until 100%. That might take a while as I can see. So you have to use IF .

    IF Solar_Power_House_W_Solar_PER <= OneHundred AND BatChargePercent < OneHundred DO // .... END_IF; 

   The difference is significant. With WHILE it will block your program till WHILE finish and other parts will not be executed for this long, in the same PLC cycle FOR might be executed so many times.

   With IF if will run FOR one time per one PLC cycle and actualy doe snot change your logic.

6. If you would share your full code or at least parts where variables you have here are used so that the whole picture is visible, you might get a better help. Edit your post and I'll edit my comment.

Answer 2

With this answer im only adressing your issue with the for loop not being executed every 50ms. The other answers why the while loop cant be exited are correct unless the variables Solar_Power_House_W_Solar_PER and BatChargePercent aren't changed in a parrellel thread.

I suggest wait is a TON function block. Please mind that names of FBs are case sensitive: wait.Q is possibly unequal Wait.Q . I think that is the main reason your for loop is not executed, because you check the output of another FB. Maybe check your declaration list for doubles with higher or lower cases.

Another possibility is, that your condition for the while loop isn't met at all and you didn't notice. In this case the for loop wouldn't be executed too of course.