Control Basics - Lauda IN 550 XT FC Operation Manual

6.4.1 Control basics

Definition
Optimizing the hydraulic system
Effects of viscosity on the heat transfer
liquid
V4
A brief explanation of terms
Actuating - Initial value of the controller to compensate for the differ-
signal
PID con- - The PID controller operates with extreme speed and preci-
troller
Proportional - The proportional range Xp indicates the temperature range
range Xp
Adjustment - The adjustment time is crucial for the I-component of
time Tn
Hold-back - The D-component of the actuating signal is formed from
time Tv
Attenuation - Attenuation time of the D-component. Rule of thumb:
time Td
Correction - Represents the maximum permitted deviation between
limitation
An important prerequisite for good control is a good connection between
the application to be temperature-controlled and the constant temperature
equipment.
Use short hoses with a large cross section to reduce the flow resistance.
n
Select a heat transfer liquid that is as thin as possible (viscosity below
n
30 mm²/s) and with the highest possible heat capacity. Precedence list:
Water, water-glycol mixture, oils, Fluorinert®.
Set pump or bypass so that the volume flow of the heat transfer liquid is
n
as high as possible.
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.
The viscosity of the heat transfer liquid changes drastically with the tem-
perature. At low temperatures, liquids are more viscous. The control quality is
therefore generally poorer at low temperatures. For this reason, the control
setting should be towards the lower end of the temperature range.
Integral process thermostats with flow control unit
ence between the actual value and target value (control
deviation).
sion and consists of a P, I and D-component.
within which the proportional component (P-component)
of the controller represents 0 - 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.
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.
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.
Td = Tv x 0.15.
the temperature at the external consumer and the tem-
perature at the outflow.
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