Configuring/address space
4.2 Pulse width modulation PWM mode
Technology Module TM Pulse 2x24V (6ES7138‑6DB00‑0BB1)
Manual, 05/2019, A5E35061186-AB
39
4.2.1.6 Dithering
The dither function is specially designed for control of proportional valves. The dither function
superimposes an adjustable symmetrical variation on the setpoint for control of the valve
solenoid. This results in a minimal motion around the set position and prevents the valve
from sticking due to stiction or hysteresis effect. This improves the reaction to setpoint
changes.
You set the parameters for the dithering in the hardware configuration. You activate the
dithering using the DITHER bit in the control interface (Page 55).
Dithering amplitude
The dithering amplitude is the amplitude of the dither signal in relation to the period duration
of the output sequence. The value range is 0 to 50%. If you set a value above the value
range, a dithering amplitude of 50% is used.
The module dynamically adjusts the dithering amplitude when the determined effective duty
cycle is greater than 100% or less than 0% so that the dither signal remains symmetrical.
Examples:
With a dithering amplitude of 10% and a duty cycle of 50%, the effective duty cycle of the
output sequence varies periodically between 40% and 60%.
With a dithering amplitude of 10% and a duty cycle of 95%, the effective duty cycle of the
output sequence varies periodically between 90% and 100%.
In addition, you can change the dithering amplitude via the control interface by entering a
new value in SLOT as integer (UDINT). In so doing, you can use the MODE_SLOT control
bit to choose whether you want to apply a change once or cyclically:
MODE_SLOT = 0 One-time change:
As soon as you write the value 6
D
in the corresponding output byte, the
value from SLOT is applied once as the dithering amplitude.
A change using SLOT takes effect after a stop and restart of the dither-
ing.
MODE_SLOT = 1 Cyclic change:
When you write the value 22
D
in the corresponding output byte, the cur-
rent value from SLOT in each case is applied cyclically as the dithering
amplitude.
A change using SLOT takes effect after a stop and restart of the dither-
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