FB_PT1

PT₁ element for smoothing of input variables.

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 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= 5s ):

Note on damping times: 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 0s means that the output variable directly follows the input variable multiplied by Kp.

VAR_INPUT

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

fIn: Input value.

fkP: Gain factor, preset value: 1.

tT1: Damping time, preset value: 10 s.

tCycleTime: PLC cycle time, preset value: 10 ms.

bSetActual: Sets the output fOut directly to the input value fIn.

VAR_OUTPUT

fOut       : LREAL;

fOut: Output value.

Requirements