Hello all, I need a support in order to develope a low pass filter on Simulink using this formula: val (new) = val (old) + (in - val (old)) * dT / T. Any idea ?

I have two input signals :

u1 = output from a 2-D lookup table

u2 = constant with one value

dT is the sample time

T is u2

and val(new) is u1( t) , where t is the time

val(old) is u2(t-1), where t is the time

Answer 1

[Nehemiae]

Hello,

The equation provided can be implemented using unit delay blocks, gain blocks, etc. I have implemented the same below, assuming a sine way as the “in” signal, and random values for dT and T.

To get the output of an LPF, the look-up table and the variables need to be tuned accordingly. The documentation on look-up tables (https://www.mathworks.com/help/simulink/slref/2dlookuptable.html) and unit delays (https://www.mathworks.com/help/simulink/slref/unitdelay.html) will help in this regard.

[Giulia]

Hello, thank you so much for your answer. It was very helpful.

I have another question to you. If i use a look-up table in my model, in this case how should i choose propertly the table data and the breakpoint 1 and 2.

Thank you again in advace.

[Nehemiae]

Hello,

Table data is the matrix of values that define how u1 and u2 (the inputs to your look-up table) are related to each other. This is defines the output of the look-up table for a particular set of inputs. So this is the known set of outputs. Then breakpoints 1 and 2 are the values of u1 and u2 that index into table data. The lengths of breakpoints 1 and 2 will be the number of rows and number of columns of table data, respectively. So these are the known set of inputs.

You can select these values to get the required working of the LPF.