Burkert 178 354, Operating Instructions Manual

Page: 29 / 89

8605 - 29
english
In order to compensate this dependence, control is effected with a PWM
frequency that is dependent on the pulse duty factor whose curve follows a
triangular function (see
illustration 8-5: PWM frequency / pulse duty factor ).
Here the frequency is lowest at the limit points (0 %, 100 %), and highest at
τ
= 60 %.
0 % 100 % 60 %
τ
f
f
LO
f
HI
Illustration 8-5: PWM frequency / pulse duty factor PWM frequency / pulse duty factor
The two limit frequencies of the PWM control (HI and LO) are set with the
selection of the valve type. The frequency actually output varies within this
range, depending on the working point.
The following values (see
illustration 8-6: Limit frequencies for Bürkert valve
types) were determined empirically from the behaviour of a large number of
individual devices of the corresponding type.