Burkert Type 8620 - Manual (Page 85)

mxCONTROL Type 8620
Page 85
14.2 General PID controller (COMMON_PID)
The general PID controller module COMMON_PID is provided for the process control with a single
actuator, e.g.:
• Flow control with a proportional valve
• Temperature control through heating or cooling.
The module is also suitable for configuring a cascade control.
These
modules
are
explained
below.
Figure 25: (COMMON_PID)
Set point preparation (Ratio, SP Adapt, CutOff, SP Limit, SP Ramp)
Depending on the type of the preferred control, this controller module can be configured both for fixed
value control with internal set point, follow-up control with external set point or cascading control.
Ratio control (Ratio) with external set point
A ratio control is a special type of follow-up control with external set point input.The task of a ratio
control is to cause a controlled variable (PV) to track another process variable (PV2, from external set
point input) within a specific ratio
Kx . PV is described as the dependent variable (controlled variable),
and
PV2
as the command variable.
In the regulated condition of the ratio control, the following equation applies:
Kx = PV / PV2
This gives the resulting set point for the controlled variable PV:
PV2 Kx Ext SP ∗ =
Set the ratio set point Kx to 1.0 for regular follow-up control with external set point.
Set point adaptation (SP Adapt) with cascade control
If this controller module is used as auxiliary controller of the subordinate control loop of a cascading
control, a conversion of the control output 0 … 100%, specified by the main controller, to a set point
with units is required for the subordinate control loop.