Oversized Staged Systems - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 15.0

Controller Tool Help

Johnson Controls
Product name
Controller Configuration Tool
Document type
User Guide
Document number
Revision date

Staged equipment offers additional challenges to the process of tuning a PID controller. Pulsing (cycling) the individual stages causes the process variable to oscillate. Without proper configuration, PRAC+ responds to these oscillations by tuning the PID controller to a sluggish state. PRAC+ is capable of tuning the PID parameters well by configuring the minimum tune band and the dead band of the PID using the control band from the multi-staged controller. However, if equipment is oversized or the minimum on/off times are large (causing the controller to be unable to keep the process variable within the desired control band), PRAC+ sees these oscillations as unstable control and increases the proportional band, causing control to be sluggish. If the control band is increased (and thus the minimum tune band and dead band of the PID are also increased), PRAC+ is able to tune appropriately.