Cascade PID Loop questions

Hi guys,

I have some questions regarding the cascaded PID loops. I am working with RSLogix 5000, and I not using the built-in master/slave functionality.


This is a pre-heater application. I would like to use the outer loop to control the product temperature, and send its output to the slave setpoint. The slave loop controls the media temperature, in this case - hot water.

My questions are as follows:

The Output of the master loop is in percent. Is this the output that I send to the slave setpoint? Basically, a move instruction with Master.OUT -> Slave.SP.

The scaling on the slave loop matches scaling of the master loop. Is this correct?

Thanks so much.

I guess the main question is there a way to get the control variable of the master in engineering units of the slave?

Download document logix-wp008.pdf from www.ab.com, this documment explains whta you´re asking.

Thanks for the reply, and I read through the document, but it is referencing the PIDE instruction. Our software is not licensed to have FBD functionality. I am stuck using PID loops and Ladder Logic.