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8.5.9
CHARACT - Selection of the transfer characteristic between
input signal (set-point position) and stroke (correction
characteristic)
With this auxiliary function, you select a transfer characteristic with regard to set-point value (set-point
position, CMD)and valve position (POS) for correcting the flow or operating characteristic.
The flow characteristic k
displacement/angle s. It is determined by the shape of the valve seat and the valve seat seal. Two types of
flow characteristics are generally realised: the linear and the equal percentile. With linear characteristics,
identical stroke changes ds are allocated to the same k
In the case of an equal percentile characteristic, a change in the valve position ds corresponds to an equal
percentile change in the k
The operating characteristic Q = f(s) indicates the relationship between the volume flow Q, which flows
through the valve installed in a system, and the displacement/angle s.
In the case of positioning for closed-loop controls, special requirements are usually placed on the course of
the operating characteristic, e.g. linearity. For this reason, it is occasionally necessary to correct the oper-
ating characteristic in an appropriate manner. Equal percentile characteristics 1:25, 1:33, 1:50, 25:1, 33:1
and 50:1 as well as a linear characteristic can be set. In addition, it is possible to freely programme a char-
acteristic curve via supporting points.
Standardised valve stroke [%] (POS)
Fig. 16:
Characteristics
8.5.10
Calibrate Position Sensor (X.TUNE) - Zero Flow Point Setting
When executing the zero flow point function, the position control is adjusted at the physical stroke of the
actuator in use. Likewise, the zero flow point must be determined manually here.
For devices that are already firmly connected to the valve body in the delivery state, the function zero
flow point setting has already been carried out at the factory.
NOTE
Execute zero flow point setting only if required.
▶ Run function only when the actuator has been dismantled or the valve body has been changed.
34
= f(s) indicates the flow of a valve, expressed by the k
v
value (dk
/k
= n
v
v
v
equal percentile
english
value changes dk
v
to *ds).
Set-point position [%]
CMD
Type 3281
Start-up
value, as a function of the
v
(dk
=n
*ds).
v
v
lin
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