Need help in Cascade control method...[/url]

Regards,

Marcjan

Anit

Dear Experts,
I am working on a project in which I have to maintain Level and Flow in tank using valve opening and closing. Level is my primary variable and flow is secondry .
How to do it??
I come to know about cascade , wethere I have to use that concept??
Pls guide me!!!

CASCADED CONTROLLER

Hello maher;
Cascade controll does not automatically make a better loop response than a simple loop; it all depends on the requirements of the loop controllers.
Here is an explanation of when a cascade controller is required:

Cascade control can improve control system performance over single-loop control whenever either: (1) Disturbances affect a measurable intermediate or secondary process output that directly affects the primary process output that we wish to control; or (2) the gain of the secondary process, including the actuator, is nonlinear.
In the first case, a cascade control system can limit the effect of the disturbances entering the secondary variable on the primary output.
In the second case, a cascade control system can limit the effect of actuator or secondary process gain variations on the control system performance. Such gain variations usually arise from changes in operating point due to setpoint changes or sustained disturbances.

A typical candidate for cascade control is the shell and tube heat exchanger

The author then proceeds to explain the shell and tube heat exchanger system, which should remind you of your own furnace cooling system, and the cascade control to be implemented.
Have a look here:
http://www.bgu.ac.il/chem_eng/pages/Courses/oren%20courses/Chapter_10.pdf

Implementing complex loop configuration with PID controllers