FB_PT1

PT₁ element for smoothing of input values.

This function block is active continuously. The output fOut always follows the input value fIn multiplied by Kp with an exponential curve:

If Kp is 1 the output value directly follows the input value. fOut has already reached 63 % of the input value after the time tT1 has elapsed, after 3 x tT1 the value is 95 %.

The mathematical formula is:

The following time-discrete formula is used for the calculation in the PLC:

With a continuously changing input fIn, fOut behaves as follows (fIn= 0..33000, Kp= 1, T1= 5 s):

Since this function block is a time-discrete model of a PT1 element, it only works correctly if the damping time is significantly longer than the set cycle time. To be on the safe side, if a damping time is entered that is less than twice the set cycle time it is internally set to zero. A damping time of 0 s means that the output value directly follows the input value multiplied by Kp.

fIn          : LREAL;
fKp          : LREAL := 1;
tT1          : TIME := t#10s;
tCycletime   : TIME := t#10ms;
bSetActual   : BOOL;

fOut     : LREAL;