IFM Electronic Ecomat Mobile Series System Manual page 181

PWM in the ecomatmobile controller
At a higher PWM frequency (standard value 250 Hz up to 1 kHz) the remaining movement of the valve
piston is so short or so slow that this effectively results in a standstill so that the valve piston can again
get stuck in its current position (and will do so!) (→ next figures):
Figure: A high frequency of the PWM signal results in an almost direct current in the coil. The valve piston does not move
enough any longer. With each signal change the valve piston has to overcome the break-away torque again.
Figure: Too low frequencies of the PWM signal only allow rare, jerking movements of the valve piston. Each pulse moves the
valve piston again from its off position; every time the valve piston has to overcome the break-away torque again.
NOTE
With a switch-on time below 10 % and above 90 % the dither does not have any measurable effect any
longer. In such cases it makes sense and it is necessary to superimpose the PWM signal with a dither
signal.
Dither frequency and amplitude
The mark/space ratio (the switch-on time) of the PWM output signal is switched with the dither
frequency. The dither amplitude determines the difference of the switch-on times in the two dither half-
waves.
NOTE
The dither frequency must be an integer part of the PWM frequency. Otherwise the hydraulic system
would not work evenly but it would oscillate.
ifm System Manual ecomatmobile SmartController (CR2500) V05
Hydraulic control in PWM
181