Siemens SIMATIC ET 200SP Manual page 83

● Dither period (μs): Assign the period duration in microseconds for the superimposed
dither signal. The allowed range is from (4 x PWM period) to 100,000 μs. Also, the Dither
period must be greater than 2 ms. If a value less than 2 ms or less than (4 x PWM period)
is parametrized, then an error occurs (see parameter validation (Page 120) for
ERR_SLOT_VAL and ERR_LD). If a Dither period higher than 100 ms is assigned, the
module will use the value 100 ms. The Dither period used by the module can only be an
even multiple of the PWM period. The module will use the nearest possible value to the
assigned Dither period.
● Dither ramps: The dither ramp parameter is one double-word made of two different
words. The low word is the dither ramp-up time and the high word is the dither
ramp-down time.
– Dither ramp-up time (ms): Assign the time in milliseconds for the duty cycle to rise
– Dither ramp-down time (ms): Assign the time in milliseconds for the duty cycle to fall
Note
Changing parameters during Dither output
If the PWM period is changed during operation using the slot mechanism, so that the dither
period is less than (4 x PWM period), then dither current is deactivated and feedback bit
STS_DITHER = 0, until a valid combination of Dither and PWM periods is assigned.
If you change parameter values using the SLOT mechanism during dither output, then you
should restart the output sequence.
Note
PWM with dithering in isochronous mode
For best results, set the dither period duration to an integral even-numbered multiple of the
application cycle.
Example: If the application cycle is 1ms, then the minimal optimal dither period is 2ms. The
next optimal values are 4ms, 6ms, ...
Technology module TM Pulse 2x24V (6ES7138‑6DB00‑0BB1)
Manual, 09/2015, A5E35061186-AA
from 0% to 100%. The allowed range is 0 ms to 30,000 ms. If a higher value is
assigned, then 30,000 ms is used by the module.
The effective ramp-up time is dependent on the dither amplitude and the nominal
value of the duty cycle.
For example: if your nominal value of the duty cycle is 50% and the dither amplitude
is 100‰, the effective duty cycle will vary between 40% and 60%, the ramp-up time
from 50% to 60% will be 100‰ x Dither ramp-up time.
from 100% to 0%. The allowed range is 0 ms to 30,000 ms. If a higher value is
assigned, then 30,000 ms is used by the module.
The effective ramp-down time is dependent on the Dither amplitude and the nominal
value of the duty cycle.
For example: if your nominal value of the duty cycle is 50% and the dither amplitude
is 100‰, the effective duty cycle will vary between 40% and 60%, the ramp-down time
from 50% to 40% will be 100‰ x Dither ramp-down time.
Modes and Functions
3.12 Function: Dither PWM output
83