ifm
System Manual
ecomat
mobile
SmartController (CR2500) V05
PWM in the ecomatmobile controller
Hydraulic control in PWM
179
Control hydraulic valves with current-controlled outputs
As a rule hydraulic valves do not have a completely linear characteristic:
Typical characteristic curve of a
hydraulic valve:
The oil flow starts at approx. 20 % of
the coil current. The initial oil flow is
not linear.
This has to be taken into account for
the calculation of the preset values for
the coil current. The functions of this
library support you here.
9.3.2
What does a PWM output do?
PWM stands for "
p
ulse
w
idth
m
odulation" which means the following principle:
In general, digital outputs provide a fixed output voltage as soon as they are switched on. The value of
the output voltage can
not
be changed here. The PWM outputs, however, split the voltage into a quick
sequence of many square-wave pulse trains. The pulse duration [switched on] / pulse duration
[switched off] ratio determines the effective value of the requested output voltage. This is referred to as
the switch-on time in [%].
Info
In the following sketches the current profiles are shown as a stylised straight line. In reality the current
flows to an e-function.
Figure: The profile of the PWM voltage U and the coil current I at 10 % switch-on time:
The effective coil current I
eff
is also 10 %
Figure: The profile of the PWM voltage U and the coil current I at 50 % switch-on time:
The effective coil current I
eff
is also 50 %
