PLC Programming

I'd need to know more about the application.

My first question is why a simple set of level control switches controlling the opening and closing a valve (or pump) feeding the tank isn't sufficient?

What are the circumstances that you are dealing with--is fluid both going into and leaving the tanks simultaneously? Are you aiming to achieve a certain depth in the tanks to achieve a certain head pressure?

Use some words, tell us what you're trying to do and the circumstances and criteria around it.

well certainly simple single loop pid controller will do, but since it comprises of 10 tanks, i might as well settle for a plc with hmi control as well (to integrate the controls) to save enough space and costs. the control scheme is the maintain a certain level as sealing liquid and the levels of the tanks ae of independent operation.

thanks

I agree with PWSlack--describe the required control philosophy.

BTW, that used to be part of what I did (create requirement specs, etc.). Where are you located, at least approximately?

What on earth in a tank needs PID control?

The first thing to do is to write a Control Philosophy document. The programming follows from it.

gentlemen, am just simply asking for an example program using the siemens pid control blocks by which i am planning to implement according to my applications, and there seemed to be lots of complicated replys. anyways, please be simple next time accordingly from a simple questions.

thanks

It has been a long time since I dealt with Siemens' products, but I seem to recall them having plenty of information, as well as help available from their reps. Certainly there are many "App Notes" or whatever they call them for something as basic and common as PID controls in many application.

This is as simple as we can make it...

http://lmgtfy.com/?q=siemens+pid+programming+example

Valski, I think that the contributors from CR4 are trying very hard, but to give you an application we do need to know what you are trying to do with the tank level.

Are we controlling the filling of the tank or the draining of the tank etc, you need to write a functional description of the process that you want to control, before we can help you further.

Cheers

Joe

ok, here's the concept: "the condensate tank from the vacuum pans should be filled with a certain level to act as a sealing water. discharge control valve will maintain proportionately the level at say 50% set point to avoid the escape of vacuum from the pans and this comprises of 10 pans/10 sealing tanks." in this concept, i will use the siemens plc s7300 and just need an example program on the pid blocks a simple one. hope i have not offended the cr4 contributors.

thanks and much appreciated

You need to write a proper functional description, by doing this you may be able to work out the solution for yourself.

So, trying to read between the lines:

• the condensate tanks are continually (or intermittently) being filled at some (uncontrolled?) rate due to the process?
• there is no urgency to getting the condensate out of those tanks back into the process--it is OK to control the discharge rate to maintain a 50% level in those tanks even if that means, for varying periods of time, no condensate is going back into the process?
• when necessary, the discharge valves can be opened fully to get rid of condensate at as fast a rate as the discharge valves and existing gravity or process head can manage?
• there is a level sensor in each tank?

I'm sure I'd have more questions after you answer these--in fact, I think one slipped my mind while I was making that list.

continuous filling and to control the disharge rate to maintain the 50% level. what determines the level is a flange type d/p cell. the discharge valves can be fully opened to gid rid of the condensate when necessary only and during shutdown of the plant which happens only every 6 months by way of manual intervention only. during operation of the plant, the controls will be put into auto operation. i just need a simple pid program example on this simple control scheme and i will have to do the rest.

thanks

To maintain a level doesn't need PID control. It needs an overflow weir. That is why the forum cannot come to grips with the problem - it cannot see why such an elaborate solution is needed when a simple one will do.

Try writing a proper functional description. The programming needed will follow, as has been stated by several readers above.

No offence has been taken here.

well taken and thanks for being supportive.