Drive functions
7.3 Function modules
Function Manual
312 Function Manual, 01/2011, 6SL3097-4AB10-0BP3
7.3.8.22 PT1 (smoothing element)
Brief description
● First-order delay element with setting function
● Used as smoothing element
Mode of operation
Setting function not active (S = 0)
Input variable X, dynamically delayed by smoothing time constant T, is switched to output Y.
T determines the steepness of the rise of the output variable. It specifies the time at which
the transfer function has risen to 63% of its full-scale value.
When t = 3T, the transfer function reaches approximately 95% of its full-scale value.
The internally fixed proportional gain is 1 and cannot be changed.
If T/TA is sufficiently large (T/TA > 10), the transfer function has the following characteristic:
Y (t) = X · (1 - e-t/T)
Constraint: t = n · TA
The discrete values are calculated according to the following algorithm:
Y
n
= Y
n-1
+ (TA/T) (X
n
- Y
n-1
)
Y
n
Value of Y in sampling time n
Y
n-1
Value of Y in sampling time n-1
X
n
Value of X in sampling time n
Setting function active (S = 1)
When the setting function is active, the current setting value SVn is accepted at the output
variable:
Yn = SVn
Note
The larger T/TA is, the smaller the amplitude change at Y from one sampling time to the
next. TA is the configured sampling time of the function block.
T is limited internally: T ≥ TA
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