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5.10
Control
5.10.1
Control basics
Definition
Effects of viscosity on the heat transfer
liquid
Influence of control parameters on the
control action
Fig. 11: Ideal setting
26 / 41
A brief explanation of terms
Actuating
- Initial value of the controller to compensate for the differ-
signal
ence between the actual value and target value (control
deviation).
PID con-
- The PID controller operates with extreme speed and preci-
troller
sion and consists of a P, I and D-component.
Proportional
- The proportional range Xp indicates the temperature range
range Xp
within which the proportional component (P-component)
of the controller represents 0 ¾ 100 % of the maximum
actuating signal. If, for example, the preset Xp is 10 K and
the control deviation is 2 K, 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
- The adjustment time is crucial for the I-component of the
time Tn
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
- The D-component of the actuating signal is formed from
time Tv
the hold-back time Tv. It influences the speed with which
the actual value approaches the target value and counter-
acts the P-component and I-component. The greater the
preset hold-back time Tv, the more intensively the output
signal is attenuated. Rule of thumb: Tv = Tn x 0.75.
Attenuation
- Attenuation time of the D-component. Rule of thumb:
time Td
Td = Tv x 0.15.
A control that is stable at low temperatures will usually be stable at high tem-
peratures. Conversely, if a system is just about stable at high temperatures, it
will most probably be unstable at lower temperatures, i.e. vibrate.
LOOP
V3
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