Enable signals

[Pablo Escobar]

I have to carry out a programming where I have some valves and it has to meet these requirements:

If the OPEN button is energized and the RETRO signal is energized, it goes to OUT
If the OPEN button is energized and the RETRO signal is not energized, it goes to FAULT

My question is, does anyone know how I can make the RETRO signal meet these characteristics?

I'm new to programming and I don't know much, I also don't know if I explained myself well haha.

I hope you can help me.

 

[Pablo Escobar]

I forgot to say that I am using the studio 5000

 

[parky]

A lot more information would be helpful, like is this valve single acting or double acting i.e. is it a pulse & opens the valve & it stays (due to the nature of the valve i.e. pulse on pulse off) or is it a single acting one where the output to the valve needs to be latched in i.e. output stays on to keep the valve open.
What happens if the retro signal goes off does the valve stay open or should it close & alarm ?.
Attached is a simple idea it assumes the valve output needs to be on for it to stay open, if the retro signal goes off the valve closes but does not alarm the alarm is latched so it can be seen by ther operator.

 

[drbitboy]

It appears that OPEN and RETRO are input signals to the PLC, and OUT and FAULT are output signals from the PLC. So if we assume the variable name (e.g. OPEN) is a proxy for the 1 (energized) or 0 (not energized) state of each input, then

     OUT <= OPEN AND RETRO;


     FAULT <= OPEN AND NOT RETRO;

where:

  "<=" assigns the evaluation of the expression on the right
        as the value of the variable on the left.


  ";" terminates a statement

 
  also:

  1 <= NOT 0;
  0 <= NOT 1;

  0 <= 0 AND 0;
  0 <= 0 AND 1;
  0 <= 1 AND 0;
  1 <= 1 AND 1;

Does that describe how you think your process should behave?

 

[parky]

Brian: you have been up too long the OP states a button to open the valve & alarm if button pressed & not Retro (what ever that is?).

 

[Pablo Escobar]

I don't know if this helps, when the operator presses OPEN and if the signal reaches RETRO then the OUTPUT is energized and the valve opens and stays that way until the operator decides to close it, that would be the first case.

The second case is if the operator presses OPEN and the RETRO signal does not arrive, then it sends a FAULT alarm, the same case is if the operator wants to close the valve and does not react.

What I need is how to make those cases come true.

 

[Blenderhedd]

Is there any kind of feedback signal from the valve?
What exactly is "retro"(another button, timer, etc)? What controls the state of retro?

 

[Pablo Escobar]

Retro would be an indicator

 

[parky]

From what I gather the retro is actually the valve open position, if that is the case then you have not explained it quite right.
Let's assume that "Retro" is valve open position then pressing the button the "Retro" will not be on as it will not have reached it's position so what you need is a timer.
It is common to use timers as a delay to allow a valve to reach it's position so instead of the button and not the Retro set an alarm just put a timer in there i.e. And Valve open solenoid and not Retro start timer, when the valve reaches the open position then the Retro should be on so the logic driving the timer will be off, if it does not reach the retro indicator then the timer will time out & set the alarm.
See pic a lot has been assumed & there are many ways to do this but if as I suspect "Retro" is a feedback limit on the valve then this will work again I have assumed once triggered the valve is held on by the output until told to close by a close button.

 

[drbitboy]

We still don't know much about the system, and I am too busy to pull teeth. This might behave similar to @parky's, but I am still tired from last night so maybe it will make a mess instead.

​

 

[drbitboy]

Retro would be an indicator

An indicator of what? That it is time to go home?

 

[drbitboy]

heh.

​

 

[parky]

Yep it's still confusing, assuming the system is a valve that has two limit sensors (Open/Closed) there is still a lot of information we need to know.
Is the solenoid that drives the valve (assuming pneumatic) a single acting or double acting it does make a difference. Single acting means the PLC output needs to stay on to keep it in the open position, turning it off allows the solenoid to close. wheas a double acting you do not need to keep either the open or closed plc output on as the solenoid acts like a flipflop.
I normally create a function block (or AOI) so that it can be used over & over again.
So I think the OP needs to explain in more detail.
I.e. What drives the valve is is a solenoid (single or double acting), is it motor driven, are the "Retro" signals the valve limit sensors.
Are there two of them (open/Closed).
Example:
I have a pneumatic valve with two sensors for open & closed.
The pneumatic valve is single acting i.e. a signal to open that stays on when turned off the valve closes.
I neen two alarms one for failed to open & one for failed to close.
The valve needs to go back to the closed position if it fails to reach the open limit.
The alarm stays on until reset either on a reset button or a press of the open button to allow the valve to try to open again.
This type of information is a must as it is impossible to demonstrate the required control the OP is after.