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22 Disposal
Control difference
The control difference is the difference between the reference
variable and the controlled variable. It is labelled with xd. The
controlled variable is calculated as follows: xd = w - x.
Controlled variable
The controlled variable is the actual value and is labelled with
x. The controlled variable represents the currently measured
volumetric flow.
Correcting variable y
Input variable for the controlled system. The process control-
ler guidance to the positioner regarding the position in which
the triggered control valve must be driven in order to achieve
the desired volumetric flow.
Derivative action time Tv
It is used to set the intensity of the D component.
Differential component (D component)
For an inverse controller (heating) the D component has the
following effects: If the controlled variable is reduced due to a
disturbance in the controlled system, the D component coun-
teracts the change by creating a positive regulation ratio. If
the controlled variable increases due to a disturbance in the
controlled system, the D component counteracts this change
by creating a negative regulation ratio. The higher the derivat-
ive action time Tv is set, the stronger the dampening reaction.
Disturbance variable z
An external variable that influences the controlled system that
normally cannot be influenced (e.g. volume flow fluctuations).
Integral-action component (I component) Ki
The I component Ki changes the controller regulation ratio
continuously until the actual value reaches the set value. The
regulation ratio will be integrated upwards or downwards as
long as a system deviation exists. The influence of the I com-
ponent will become larger the longer a system deviation ex-
ists. The shorter the reset time Tn and the larger the system
deviation, the stronger (faster) the effect of the I component.
The I component hinders a constant system deviation.
Proportional action factor Kp
Instead of the designation proportional band, the expression
proportional-action factor Kp is used frequently. Conversion
of Xp to Kp is: Xp = 100[%]/Kp or Kp = 100[%]/Xp The Kp value
indicates how much the controlled variable x changes if the
correcting variable y is adjusted. Kp = ∆x/∆y = x2 – x1/y2 – y
In order to obtain a unit-independent relationship in the equa-
tion above, x and y must be divided by their respective max-
imum values (100%). In this case, a high Kp value results in
smaller deviation. However, if the Kp value is set too high, it
leads to an increased tendency for the control circuit to oscil-
late.
Proportional band Xp
The proportional band tells us the extent to which the con-
trolled variable x changes when the manipulated variable y is
adjusted. Xp can be used to adapt the controller amplification
to the controlled system. If a small proportional band is selec-
ted, it has a large manipulated variable y (e.g. 20 mA) as a res-
GEMÜ 1436 cPos
ult, i.e. the positioner reacts faster and harder with a small
proportional band. If a too small proportional band is chosen,
this leads to oscillation of the control circuit.
Reference variable
The reference variable is the set value and labelled with w.
The reference variable is the input variable of the control cir-
cuit. The reference variable must follow the controlled vari-
able in the specified dependence.
Reset time Tn
The reset time Tn determines the duration how long a system
deviation is adjusted. If a high value is preset for the reset
time Tn this means a small influence of the I component and
vice-versa. During the reset time Tn the controlled variable
change caused by the P component is added again. Thus
there is a fixed relationship between the P component and the
I component. If the P component is thus changed, the time re-
sponse changes too if the Tn value remains constant. Ki = 1/
Tn
22 Disposal
1. Pay attention to adhered residual material and gas diffu-
sion from penetrated media.
2. Dispose of all parts in accordance with the disposal regu-
lations/environmental protection laws.
23 Returns
Legal regulations for the protection of the environment and
personnel require that the completed and signed return deliv-
ery note is included with the dispatch documents. Returned
goods can be processed only when this note is completed. If
no return delivery note is included with the product, GEMÜ
cannot process credits or repair work but will dispose of the
goods at the operator's expense.
1. Clean the product.
2. Request a return delivery note from GEMÜ.
3. Complete the return delivery note.
4. Send the product with a completed return delivery note to
GEMÜ.
70 / 76
www.gemu-group.com
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