Burkert 8694 - Page 68

68
Operation and function
Theowcharacteristick
V
=f(s)indicatestheow-rateofavalve,expressedbythevaluek
V
as a function
of the stroke s of the actuator spindle. It is determined by the design of the valve seat and the seat seal. In
generaltwotypesofowcharacteristicsareimplemented,thelinearandtheequalpercentage.
In the case of linear characteristics, equal k
V
value changes dk
V
are assigned to equal stroke changes ds.
(dk
V
= n
lin
⋅ ds).
In the case of an equal percentage characteristic, an equal percentage change of the k
V
value corresponds
to a stroke change ds.
(dk
V
/k
V
= n
eqlprct
⋅ ds).
TheoperatingcharacteristicQ=f(s)speciesthecorrelationbetweenthevolumetricowQintheinstalled
valve and the stroke s. This characteristic has the properties of the pipelines, pumps and consumers. It
thereforeexhibitsaformwhichdiersfromtheowcharacteristic.
Position set-point value
[%]
Standardized valve stroke [%]
Figure 49: Characteristic
In the case of control tasks for closed-loop control systems it is usually particular demands which are placed
on the course of the operating characteristic, e.g. linearity. For this reason it is occasionally necessary to correct
the course of the operating characteristic in a suitable way. For this purpose the positioner features a transfer
elementwhichimplementsdierentcharacteristics.Theseareusedtocorrecttheoperatingcharacteristic.
Equal percentage characteristics 1:25, 1:33, 1:50, 25:1, 33:1, and 50:1 as well as a linear characteristic can
be set. A characteristic can be freely programmed using nodes.
english
Type 8694 REV.2