Operating instructions
6.10
Control
The internal and external control parameters are preset at the fac-
tory for operation as circulation chiller (with water as heat transfer
liquid). Depending on the application, adjustments of the control
parameters can be necessary from case to case. The thermal
capacity and the viscosity of the heat transfer liquid also influence
the control behaviour and may require adjustment of the control
parameters.
6.10.1
Basics
Control
value
- Output value of the controller to compensate for the dif-
ference of actual value to setpoint (control deviation).
PID
con-
troller
- The PID controller operates very precisely and consists
of P, I and D parts.
Propor-
tional
range
Xp
- The proportional range Xp specifies the temperature
range in which the proportional part (P part) of the con-
troller is 0 ... 100 % of the maximum control value. For
example, if the control deviation is 2 K for Xp set to
10 K, the P part is 20 % of the control value. In the
case of a control deviation of 10 K and more, the P part
is 100 % of the control value.
Reset
time Tn
- The reset time is decisive for the integral part (I part) of
the control value. It specifies the interval in which an
existing control value is integrated. The larger Tn is, the
slower the control deviation is integrated. Thus, the
control is slower. A smaller Tn makes the control more
dynamic and finally results in oscillations.
Lead
time Tv
- The differential part (D part) of the control value is
formed from the lead time Tv. It influences the
approach speed of the actual value to the setpoint and
counteracts the P and I parts. The larger the lead time
Tv is set, the stronger the output signal is damped. As
rule of thumb. the following applies: Tv = Tn x 0.75.
An important prerequisite for acceptable control quality is well-
designed hydraulics. Therefore, an as good as possible connection
between the application to be temperature-controlled and the tem-
perature control device must be established. This means:
Only use approved heat transfer liquids: water or water-glycol.
Use short tubes with large cross section. This reduces the flow
resistance. A lot of heat transfer liquid can circulate in a short
time, thus the circulation time is short.
Use bypass of the device to increase the flow rate of the heat
transfer liquid.
Explanation of terms
Optimising hydraulics
Operation
Variocool 49