Lauda VC 1200, Руководство по эксплуатации

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Only use approved heat transfer liquids: water or water-glycol mixture.
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Use short tubes with large cross section. This reduces the flow resist-
ance. A lot of heat transfer liquid can circulate in a short time, thus the
circulation time is short.
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Use bypass of the device to increase the flow rate of the heat transfer
liquid.
The viscosity of the heat transfer liquid changes very quickly with the tem-
perature. The liquids have higher viscosity at low temperatures. Therefore,
the control quality is generally worse at low temperatures. For this reason,
the controller should be set at the lower end of the temperature range to
be covered. If the control is stable at low temperatures, then it is generally
also stable at high temperatures. On the other hand, if a system is just still
stable at high temperatures, it is highly probable it will be unstable at low
temperatures, i.e. it oscillates.
If, for example, the operating temperature range of a system is
-20 – 80 °C, then the controller setting should take place at
-10 – 20 °C.
The picture on the left shows optimum setting of the control parameters.
If the Xp parameter is selected too large, the actual value reaches the
proportional range early and the P part becomes smaller than 100 % of the
control value. The approach to the setpoint slows down. Thus, the simultane-
ously integrating I part has more time to build up its control value portion. If
the setpoint is reached, the I part summed too much results in overshooting
beyond the setpoint. If the proportional range Xp is reduced, the P part
remains at 100 % for longer. Therefore the actual value approaches the
setpoint more quickly and the I part has less time to integrate the control
difference. The overshooting is reduced.
Other precautions
Indications of incorrect settings
Fig. 32: Optimum setting
Fig. 33: Control parameter Xp too large
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