Pid Cascade Loops Rslogix 5000

Hi there,

I need to wite the logic to control a cascaded PID loop with the following characteristica:

1- Master : Density
2- Slave : Water Flow

the customer requires that this loop has the following modes:

1- Master (Auto / Man / Cascade)
2- Slave ( Auto / Man / Cascade)

According to Rslogix 5000 Help menu, When you connect the two loops in cascade foramt, and in configuration tab choose the master and slave, and put them in automatic mode the two loops work in cascade mode.

However my client requires that that the loops, espacially the slave must have the "AUTO MODE" ,with independant set point, so he can tune the flow loop independantly ,using the flow transmitter.

My questions are:

1- is there a good reference regarding cascading loops in RSLOGIX 5000 to refer to.

2- When a loop is configured as SLAVE, Wouldn't "Auto mode" put it into Cascade mode automatically. basically, I would like to know if a loops is configured as a Slave cascade loop, how can it have independant Auto mode with separate set point.

Regards

Why not set up the loops as Cascade the old way; 2 seperate
loops. Then provide the option of moving the output of loop
1 to loop 2.

This is how we do things which is not to say you can't do this
with the Cascade feature of CLX.

Good Luck,

(8{)} .)

(Yosi)

Can you use PIDE or are you stuck using PIDs?

Learner,

I just went through a similar process and posted the same question here. The consensus was that the Master/Slave setup in Logix5000 is too constraining for doing what you describe. As the second poster said, do it the old fashion way. That's what I did. Treat them as seperate loops with the output of the outer loop going to the setpoint of the inner. When you want to run in inner only, use a different manual setpoint for the inner loop. When you want to run pure manual, put the loops in SWM mode.

ghettofreeryder said:

Can you use PIDE or are you stuck using PIDs?

Click to expand...

I can use PIDE.

Thanks,

I think the idea of having them as two separate loops would work.

Thanks