Equipment phase

Hi All

If i devide prodedure into phases,and have a phase e.g. agitation
main
.
.
.
phase1:agitaion
phase2:fill water
.
.
.
all phases are time limited to verify that the equipment works.
what is the correct way to implement this if in phase1 the agitator should work for certain period of time and filling water phase continue while agitator is on.
should i add phase to turn off agitator? not a good idea...

Have the agitator "phase" be independent, it will start and stop based upon your logic, the water fill is another independent phase, it too will have it's on start and stop conditions.

You could do something like:
Start agitation and run until stop condition is met.
Start water fill if agitation is on and drain valve is closed, and water level is less than desired amount.
Stop water when delivered amount is >= desired amount.


Just an example, you application will be unique.

If the actions should always run together, the easy thing to do is create a single master phase/state. You might call your example FillAgitate or something similar. If the actions run indepdendently, you may need to create two states and interlock them as necessary.

A small tip - use a single master state timer. Reset the timer whenever you change states. You can then use the same timer to check a state has completed (time < limit) or to finish off a timer-based state (e.g. agitate for 10s).

Hi

What you mean by interlock?
Do you mean something called "mutex" in mutlithreading programming?

Thanks

interlock: To connect together so that the individual parts affect each other in motion or operation.

Equipment Phase

Briana,

I am not sure why do you think that adding a separate phase is not good.

I would make the water fill as an independent phase and agitator as an dependent phase. I would have stop phase to stop the independent phase i:e water fill. The dependent phase will stop as soon as the water fill is completed(timer is required to ensure that agitator phase is not stopped as soon as the water fill is completed). Alternatively an operator prompt can be given along with the timer to stop the agitator phase. All depends upon how flexible your batch manager is.

Appreciate your comments .

Briana,

The calls to the functionality you are speaking of should be handled in the batch engine(i.e. InBatch, iBatch, RSBatch, etc.). You only need to develop the PLC logic that will execute the phase(i.e. run agitator, fill water, etc) and these executable phases are called by your batch engine as the recipe requires. This goes back to what Ken mentioned about the phases being independent. What you don't want to do is have logic from one phase entwined with that of another. The only time you would have this is in the logic that sets the phase to interlocked. For example, you want to interlock the heat phase when the cooling phase is active, and vice versa. You should then use the batch software recipe creator to write your recipe which will make the individual calls to the phases as required.

Which batch software are you using for this project? Regardless of the package, it may be a good idea to attend a training course to understand how batching software and PLC logic are related.

Hope this helps,
Jeff

Hi

Its a small project therefor i have to create my own batch
engine.

Hello Briana;

What you are trying to do looks a lot like Grafcet (also known as SFC); it is part of the IEC61131-3 "standard". so it can be found as an add-on programming tool in certain PLCs (Siemens, Rockwell, Telemecanique), but it is also a great design tool (pen and paper stage) for programmers.
Have a look at what a drilling machine sequence looks like in Grafcet:




Steps (S1...S7) are where you determine the actions to be taken by your controler; in this case, Set and Reset bits; you could also call functions, write analog values to a drive...
Transitions (T1...T7) are the logic conditions to pass from one step to another; to go to step 2, step one must be active AND conditions of transition one must be true.
The layout of the sequence need not be linear; in the example, step 7 can be either activated or skipped, depending on the status of transitions 3 and 7 (notice that these are mutually exclusive, so only one path can vbe chosen at each repetition of the sequence).
There are formal ways to translate a Grafcet into Ladder, but depending on the complexity of the sequence, sometimes it is not necessary to go through this; simple application is possible, especially if the design of the sequence is clear and simplified.

See if this can help out in your project.
Hope this helps,
Daniel Chartier

Hi

If i need to agitate for certain period of time
is it wise to put the timer within the phase
or better put it in the main routine?

Thanx

There really is no need to have two phases. One phase could switch agitation on and off when it needs, open and close fill valves, monitor etc.