Why is my signal builder not giving precise outputs?

I have a signal builder block with the following signal:

I connect my signal builder block to a "To Workspace" block.

I am using a fixed step solver with sample time of 0.05s. Hence, the output variable "simout" should contain the values of the signal at every Peak and Trough, that is, it should only contain 0's and 1's.

However,  at certain time steps my output contains 0.999999999999999 instead of 1 and 1e-5 instead of 0.

Why is the output from my Signal Builder block not precise?

 

 

Answer 1

[MathWorks Support Team]

By looking at "simout.Time" we can see that the time step taken by Simulink is slightly different than the time specified in the Signal Builder. This small value forces Simulink to interpolate between the specified point, leading to the small difference you see.

Following are two workarounds:

1. Specify your signal and time values as described in the documentation. Run the following command in MATLAB R2017b to access the documentation:

>> web(fullfile(docroot,'simulink/ug/import-data-to-test-a-discrete-algorithm.html'))

Or access the latest documentation by referring following link.

https://www.mathworks.com/help/releases/R2022b/simulink/ug/import-data-to-test-a-discrete-algorithm.html

2. Use the Signal Editor block in place of the signal builder block. This is a new block that covers some of the functionalities of the Signal Builder block and we would be interested to know if this addresses your needs.

https://www.mathworks.com/help/simulink/slref/signaleditorblock.html?s_tid=doc_ta

Answer 2

[Naveen Venkata Krishnan]

This issue can be solved by using a signal editor block instead of signal builder block. The cause of the issue is because of interpolation and this option is not availbe in signal builder block.

Interestingly, it seems data from excel cannot be imported into signal editor block.

Hence we need to import data from excel into signal builder block convert it into signal editor block and uncheck interpolation in signal editor block. The below peice of code can be used to convert a signal builder block to signal editor block.

sbBlockH = [gcb]; % gcb is signal builder block path

seBlockH = signalBuilderToSignalEditor(sbBlockH,'Replace',true,'FileName','test2.mat');