How many of you have used cascaded loops?

[mordred]

http://x31eq.com/matritut.htm#algebra

I found this site was helpful on the matrix tansforms though basic in its expalinations and examples. It did help when I was studying this for understanding one of Jack Hughes books on robotics.

http://www.intmath.com/Laplace-transformation/1a_Unit-step-functions-definition.php

This one helped remind me of some the Lapatase transforms, Been awhile since I covered that subject so had to review the basics. Just some helpful links for others trying to understand whats going on. I've got a pretty good idea after working on it during the weekend as well as reading all the posts a few times. Though not 100% aware of the hardware invlved I had to look up some of the motion control basics involving the poles etc.

 

[Peter Nachtwey]

Get Scilab or wxMaxima. They are free.

 

[Roy Matson]

It never ceases to amaze me how whenever this subject comes up the mathmaticians jump on board and confuse the heck out of it trying to impress each other about how well they understand what's going on.
When I was taught to tune loops we did it by observation and simple explanations of what was happening. I guess all these years I have been doing it wrong LOL.
You know what they say about old dogs.

 

[mordred]

Well calling me a mathemtician would be the wrong guess LOL however it is a means to understanding. Much like yourself the tuning I usually do has been manually however this is usually a hit and miss method. I didn't know Scilab was free lol would have saved me tons of time ah well the practice was good for the karma

 

[Peter Nachtwey]

Well calling me a mathemtician would be the wrong guess LOL however it is a means to understanding.

Yes, and you can't control what you don't understand.

I didn't know Scilab was free lol would have saved me tons of time ah well the practice was good for the karma

At least you got something good out of this.
Scilab sure beats doing simulations in an Excel spread sheet. I still find that the symbolic formulas for the gains must be derived in Mathcad or wxMaxima.

 

[Jason A Jensen]

Favorite Cascades Control Loop:

Level.

Your tank level sets your flow rate. Your valve maintains the rate using a flow meter. It does cost you a flow meter and some IO, but it works a lot better.

Most interesting Cascaded Control Loop

Density.

My density meter set my flow rate to control my valve. Worked very well.

Over a period of 2 weeks with a density setpoint of 32.00% my loop never deviated more that 0.15%. The application was in an ethanol plant for making slurry.

 

[Peter Nachtwey]

Good Applications.

Favorite Cascades Control Loop:

Level.

Your tank level sets your flow rate. Your valve maintains the rate using a flow meter. It does cost you a flow meter and some IO, but it works a lot better.

Yes, these are the easy ones. In your case the flow changes faster than the level. I get involved with hydraulic systems that are similar in that there is a spool control loop for the spool position and an outer position loop. One can make these simple one go by the seat of your pants. I the hydraulic case the valve spool changes much faster than the position. What makes the hydraulic case a little more challenging is that the flow is not proportional to the spool opening alone but to the spool opening time the square root of the pressure drop.

Most interesting Cascaded Control Loop

Density.

My density meter set my flow rate to control my valve. Worked very well.

Over a period of 2 weeks with a density setpoint of 32.00% my loop never deviated more that 0.15%. The application was in an ethanol plant for making slurry.

That is a new one to me. So the flow controls density. This too seems like a classic in that the flow will change much faster than the density but a lot depends on the flow rate relative to the volume of fluid. The flow must be mixing with something else to control density.

Jason just made me think of a good Friday Night Quiz!!! Get your mixing and bleed and feed thinking hats on.