MATLAB Answers

How can I detect a sign change without detection of 0 holding (Simulink)

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Nick on 14 Apr 2016
Commented: Nick on 18 Apr 2016
I want to detect sign changes with Simulink blocks. By using the common libary, I also detect when the signal jumps from positive to 0, hold 0 and rises back to the positive area, which is not beneficial in my case. Do you know a way how to detect sign changes with real zero passings?


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Answers (1)

Anish Mitra
Anish Mitra on 18 Apr 2016
You can make use of the "Detect" blocks in the Simulink>Logic and Bit Operations library.
>> web(fullfile(docroot, 'simulink/slref/detectfallnegative.html'))
These blocks are for Fixed Step solvers. If the logic needs to be implemented using Variable Step solvers, then you can use a Memory block to construct the logic. Essentially this would mean taking the product of the signal, and the signal delayed by 1 (using a Memory block, not a delay). If the sign of the product is negative, it means that there is a zero crossing at that particular time step.
Hope this helps.

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Nick on 18 Apr 2016
Hi Anisha,
thank you for your suggestion. In case there are two zero sample points in a row, this detection won't work.
I solved this problem by saving the last non-zero value and thought there might be a better solution (a block from the libary).
Cheers, Nick.

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