Pneumatic Valve Control PLC logic(Step7)

Hello,
i would like to control a pneumatic valve based on conductivity of the medium in the pipe.
I want to receive OPEN and CLOSE feedback as well as do manual operations on the valve.
Kindly help with the logic

BR

I think we need more information, first of all, what are you measuring the conductivity is it an analogue signal, then you really need a proportional control of the valve, not open/close. State exactly what you want to achieve.
Is this a mix of chemical and water. so many questions.
The only time I have seen an on/off valve used in this type of application is in a CIP batching operation, for example, the tank is filled with water and when min level is reached the system recirculates the solution with the conductivity probe in the recirculation loop, The valve feeding the caustic concentrate is opened while the measurement is below the required level. this is achieved in various ways by a dosing pump at a given rate or variable speed controlled by a PID loop for more accuracy. Often for CIP makeup the process will use an on/off valve & when the recirculating solution reaches a concentration - inflight factor the valve will close, If the solution concentration falls below a certain level then the valve will open. CIP solution is not that critical in most cases so a required concentration of 1% or 50ms the in-flight factor may be 0.9 % or 45ms before shut off (to allow for latency in the recirc loop) and allow it to fall to 0.75% or 37ms before opening the valve again, you could also use a PID converted to pulses where the mark/space ratio is changed.
(before anybody complains about the conversion of % & ms cannot be bothered to work it out so this is just a guess). The figures used for the dead band can be tuned to reduce the range it falls outside the setpoint.
Note: there will be a minimum deviation allowed so many systems should the concentration become outside the allowed limits stop the feed to whatever process it is feeding.
So to re-iterate, What is the process doing i.e. batching, in-line process, allowable conductivity limits for safe or correct solution. and as much information as possible. Be aware that most on this site will help people who are stuck but do not like being used as unpaid programmers.

Hello Jethro,


What have you done so far to get this to work, where are you stuck?


To reiterate what Parky said, we are here to help you and answer questions, not solve your problems. If you would like for one of us to do your job/homework, please let us know and I am sure someone would be willing to offer you a quotation.


Also, please and thank you go a long way here.

boneless said:

Also, please and thank you go a long way here.

Click to expand...

Hello boneless: I quite like this statement. I have been thinking of starting an Other Topics rant to express disappointment at posts on which someone asks something more or less complex, some of our colleagues invest time an effort in writing words of wisdom and then nothing at all from the person who started the post.