Nested automatic mode

Hi all,
I have a system that works either in Automatic mode or in Manual mode.
There is a valve that must be able to be set as Manual (its own manual mode) while the system is in Automatic mode.
No big deal, but I was trying to find an elegant way to set the valve in ITS Automatic mode when the SYSTEM is changed to Automatic, but after that moment the valve can be set as Manual again (and then back to its Automatic mode, and so on).
I also wanted a way to turn the valve to its Manual mode when the system is turned to Manual, and not let the valve change to its Automatic mode while the system stays in Automatic.

I know it is only a matter of time to find the solution to it, but I am in the field (yes, during the weekend)...

Thank you very much!!!

I'm sorry Elcan but all I can think of (see picture below). I did read it three times and my head started to hurt. I'm sure the more serious and focused forum members will have a solution for you.
Oh and BTW I am at home ( yes, during the weekend).

So, in manual mode you're really just forcing the output to either on or off correct?

What is so hard in removing that force when the system transitions into automatic? Same with applying a force when the system is turned to manual?

Sorry if I was not clear. I will try to improve my explanation:
System in Manual Mode => Valve always in Valve Manual Mode
System transitions to Auto Mode => Valve is set in Valve Auto Mode.
System in Auto mode => Valve can stay in Auto Manual mode or changed to Manual
System transitions to Manual mode => Valve is set in Valve Manual mode and forced to stay that way.

Paully, when you say "force", you mean latch?
I'm glad you are home Mickey. Enjoy your family!

What are the specifics of you system? Ie. what type of valve? How is the valve controlled? What determines auto/manual modes? Are you using a logic controller? What type of process is this used on?

Elcan said:

Sorry if I was not clear. I will try to improve my explanation:
System in Manual Mode => Valve always in Valve Manual Mode
System transitions to Auto Mode => Valve is set in Valve Auto Mode.
System in Auto mode => Valve can stay in Auto Manual mode or changed to Manual
System transitions to Manual mode => Valve is set in Valve Manual mode and forced to stay that way.

Paully, when you say "force", you mean latch?
I'm glad you are home Mickey. Enjoy your family!

Click to expand...

Ok here is how I read this;

1)If (Manual Mode = true) then (Valve Manual Mode:= true)

2)If (Manual Mode transistions from true to False) then (Valve Auto Mode := true)

3)If (Valve Manual Switch= true) then (Valve Manual := true)


If what I describe is what you want then your going to need a "one shot falling edge" for the second line.

One shot falling edge means the PLC looks for a "transistion" from 1 to 0 and for one scan changes the output value on that line.

For the third line your going to need to use a "one shot rising". Does the same as "one shot falling" but looks for a transistion from 0 to 1.

Since I do not know what PLC you are using that is about as descriptive as I can get.

Also Manual Mode, Auto Mode, and Valve Manual Mode need to be bits (boolean functions) for this to work.

Hope this helps.

Elcan said:

System in Manual Mode => Valve always in Valve Manual Mode
System transitions to Auto Mode => Valve is set in Valve Auto Mode.
System in Auto mode => Valve can stay in Auto Manual mode or changed to Manual
System transitions to Manual mode => Valve is set in Valve Manual mode and forced to stay that way.

Click to expand...

I highlighted the parts that are somewhat unclear. It sounds like you simply need a separate mode control for a particular valve, that is interlocked with the system mode.

Is this correct:

It should not be too hard to write that logic.

I would use latch/unlatch instructions for the valve Auto mode.

When the system is placed in auto mode, use a one shot rising instruction to latch the valve mode in auto.

Same thing for manual mode, only without the oneshot.

When the operator requests to change the valve mode, ensure that the system mode is in auto before allowing it. (XIO "system auto" in the rungs)

Paul

Help you for the help!
This is what I have made so far.
Please take a look and see if I am on the right track.
The Plc is a Micrologix 1100.

Think you made it a bit complicated

Ok lets see if I get what you are trying to do. You have 3 buttons,
1--System Auto SW
2--System Manual SW
3--Valve Manual SW

and from these 3 buttons you want to control the mode of the Valve.
Your Modes are
1--System in Auto
2--System in Manual
3--Valve Auto Mode


i\If I am understanding your system correctly here is what I would do

 

System Manual Valve Auto Mode

----| |---------------------------------(Reset)

Valve Manual SW |

----| |-----------

 

 

System Auto One Shot Valve Auto Mode

---| |------------[OSR]---------------(Set)

Now you noticed I used a one shot a bit different from yours.
The OSR function works the same as the one you programed but only requires 1 bit.

Also if your valve goes to manual in Auto your valve will stay in manual until you go back to manual and then back to auto.

Notice I only used the button Valve Manual SW. Your program does not show this but you have to have some change to decide you want the valve in manual mode while your System Mode is Auto. Whatever existing critera will work just put it in place of the Valve Manual SW.

I did a sample using Mitsubishi FX1S PLC. If you're interested I can post it here. Just simple ladder diagram.