ControlMaster CM30, CM50 and CMF310
Universal process controllers,
1
/4,
1
/2 DIN and fieldmount 7 Advanced Level
IM/CM/ED–EN Rev. X 49
…Control / …Loop 1 (2) Control
Control Type Selects the basic type of controller required.
PID
Standard proportional, integral and derivative control.
pPI
pPI controller:
pPI (predictive PI control) is a deadtime-compensating control for use when the process
deadtime is longer than twice the dominant process time constant. Unlike other deadtime
compensation algorithms, pPI does not require a process model to be specified; it creates
its own process model from proportional, integral and deadtime settings. If the deadtime is
varying, the pPI controller can be combined with gain scheduling. The Autotune function is
not used when pPI control is configured.
The pPI controller is easy to tune, first by making a step response test on the process and
then setting the controller parameters by observation. After tuning, the pPI controller can be
adjusted manually. In most cases a decrease in proportional band or a decrease in integral
time gives faster control but poorer damping.
From a steady state condition, make a step change in the output from the neutral value (u0)
to a new value (u1). Observe the process value (y) and make the following calculations:
By determining the 4 key parameters: L, T, y and u from a step response, the 3 process
parameters: static gain K
p, dominant time constant Tp and deadtime Lp can be determined
according to the following expressions:
Knowing these, the pPI's parameters can be calculated easily:
Proportional band = 100 x Kp
Integral time = Tp
Derivative (deadtime) = Lp
Notes.
y0 and y1 are expressed in % of engineering range.
When pPI is selected, the derivative time is used to set the deadtime.
On/Off
A simple 2-state control.
pPI Controller
Process
Model
Model Without
Deadtime
Deadtime
I
P
OP
SP
PV
To Next Page
Loading...
Need help?
General
