PID Calculation

This has already been answered on CR4 before. A google search of "PID tuning" also produced the answer in the first hit.

I want to do all the calculation from very begining until PID tuning. I cant find the website which shown all the calculation. Which web should i go to?

From 'the very beginning' is rather vague but I think you mean water flow calculations (which is a separate topic and unlikely to be on the same website as PID tuning).

There is a lot of basic knowledge in a number of areas you need to know first (there is a reason engineers train for years rather than just going to a website for all the answers).

Try previous threads on CR4 (I believe this has been covered in part at least) and a google search of fluid or liquid flow calculations (for a more detailed guide to valve and pipe sizing for a flowing liquid).

http://en.wikipedia.org/wiki/Fluid_dynamics

http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

http://en.wikipedia.org/wiki/Valve

http://www.pipeflowcalculations.com/

etc.

how do i combined "the thinking" of water flow with PID tuning.

As i search, water flow can be controlled by PID controller, is it PID controller is to stabilization of the water flow?

See my previous comments regarding valves. A valve is an element which allows liquid to flow thru it at various rates. Valves come in two basic types - on/off and variable flow. PID control of a suitable variable flow valve will allow you to alter the amount of liquid flowing thru the valve (hence flow control).

For your application are you sure you don't just want simple on/off control to control the level of a tank? This is THE most common method and doesn't require a PID controller (just a level float switch or similar.

Please provide much more information on your application, what do you actually want to achieve and what are you trying to fill? Is this a school project as from your comments you don't seem to fully understand what PID control is and where it is used.

http://en.wikipedia.org/wiki/PID_controller

Please provide more information.

At first, i think to do water control by using PID controller as my project. As it is too simple, so i think to implement this basic to water plant as the control of water flow to used plant. As i reserch on net, water plant can be controlled by PID controller.

I plan to do the mathematic calculation on compared the P,PI,PID control. But not seem like i am in the wrong direction. As i studied, if wan to do the PID control need transfer function.

i am starting to comfuse where should i start and what to do next.

If you are getting confused start back at the basics

http://en.wikipedia.org/wiki/PID_controller

As for PID control it can be entirely implemented, simulated and displayed using software alone using the three basic P, I and D formulas (see above link).

Read the information in the above link carefully (a few times). All the information you need to understand and implement PID control is there, but if you don't understand the basic concepts of PID it will not make sense.

Remember (for say a water example), the SP is what you want the output to be (eg- flow of 100 L/min), the PV is what the output actually is and the MV is what you set the variable water valve opening too to allow the water to flow (a clearer example of MV would be a variable heater heating an oven to a specific temperature).

Do you understand the point of PID process control and why in a real world process like temperature control or liquid flow there will always be PV overshoot because the MV cannot change instantly when the PV reaches the SP. The whole point of PID control is to minimise the overshoot and stabilize the output around the SP

If this is still confusing have a further look on the internet for more PID tutorials (ignore the PID controller tuning ones and concentrate), some have diagrams that will make what I have written above clearer.

i understand of the concept of PID controller.

I got a PID controller simualator with adjecting the Ki,Kp and kd to meet the desired output. but in the simulator, it require a transfer function block. Example: mass spring transfer function is 8/(2s3+7s2+10s+3). So, is that water also got such transfer functin represent of it?

The PID controller will be there to maintain a constant flowrate.

Use the Ziegler-Nicholls method to tune it.

is that mean that i need to find the flow in transfer function, then to put on the PID controller to tune?

water in water tank is that sonsider incompressible flow?

The above method is a practical one, and needs nothing other than some sort of timing device and some simple arithmetic to tune the controller in real time. Transfer functions and S-plane algebra are all very well, though completely unneccessary with this method.

How to proved in theoretically as the P,PI and PID controller is more useful.

As i planed, i dun think to do any in hardware. i just want to do in calculation and software part.