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

Hi,

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?

Thanks.

Answer 1

[Anish Mitra]

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.

Anish

[Nick]

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.