Lauda L 100, Operating Instructions Manual

Page: 28 / 48

5.10 Control
5.10.1 Control basics
A brief explanation of terms
Actuating
signal
- Initial value of the controller to compensate for the
difference between the actual value and target
value (control deviation).
PID con-
troller
- The PID controller operates with extreme speed
and precision and consists of a P, I and D-compo-
nent.
Proportional
range Xp
- The proportional range Xp indicates the tem-
perature range within which the proportional com-
ponent (P-component) of the controller represents
0
¾
100 % of the maximum actuating signal. If the
preset Xp is 10 K and the control deviation is 2 K,
for example, the P-component is 20 % of the
actuating signal. If the control deviation is 10 K or
more, the P-component is 100 % of the actuating
signal.
Adjustment
time Tn
- The adjustment time is crucial for the I-component
of the actuating signal. It specifies the interval at
which an existing control deviation is integrated.
The higher the Tn, the slower the control deviation
is integrated and the more sluggish the control
becomes. A small Tn makes the control more
dynamic and eventually results in vibrations.
Hold-back
time Tv
- The D-component of the actuating signal is formed
from the hold-back time Tv. It influences the speed
with which the actual value approaches the target
value and counteracts the P-component and
I-component. The greater the preset hold-back time
Tv, the more intensively the output signal is attenu-
ated. Rule of thumb: Tv = Tn x 0.75.
Attenuation
time Td
- Attenuation time of the D-component. Rule of
thumb: Td = Tv x 0.15.
A control that is stable at low temperatures will usually be stable at
high temperatures. Conversely, if a system is just about stable at
high temperatures, it will most probably be unstable at lower tem-
peratures, i.e. vibrate.
Definition
Effects of viscosity on the heat
transfer liquid
Operation
LOOP 28