Equipments (Devices) > SCA06 > Ladder > Filter

Block that filters the input using a low pass filter of first order and inserts the result in the output.

Ladder Representation

LOWPASS_block

Block Structure

Variable Type	Name	Data Type	Description
VAR_INPUT	EN	BOOL	Block enabling
	Input	REAL	Input signal
	Tau	REAL	Filter time constant
	Ts#	UINT	Sampling time [ms]
VAR_OUTPUT	ENO	BOOL	Output enabling
VAR_OUTPUT	Output	REAL	Filter output
VAR	LOWPASS_INST_0	LOWPASS	Instance of access to block structure

Operation

When this block has a TRUE value in EN, filters the input value of Input using a low pass first order filter described by Tau and Ts#, inserting the result in Output. On the leading edge of EN, Output receives zero.

When EN has FALSE value, Output remains unchanged.

The ENO value forwards to the next Ladder block the EN value after the operation is completed.

Block Flowchart

LOWPASS_flowchart

Example in Ladder

LOWPASS_example02

The above example causes OUTPUT, by identifying a leading edge in EN, to display a behavior of first order with time constant equal to Tau and the sampling time of 2 ms, in order to achieve the reference set to INPUT. At each calculation completed successfully, the ENO output is activated.

LOWPASS_example01

Example in ST

The example below displays the instructions for applying the example above in the ST language.

VAR

INPUT : REAL := 10.98;

TAU : REAL := 5.0;

OUTPUT : REAL;

LOWPASS_INST_0 : FB_LOWPASS;

END_VAR

LOWPASS_INST_0.EN := DI1;

LOWPASS_INST_0(Input:=INPUT, Tau:=TAU, Ts:=2);

OUTPUT := LOWPASS_INST_0.Output;

DO1 := LOWPASS_INST_0.ENO;