array subtraction returns 0 value

[sxy248]

Hi,  

I am writing a code to take spectrum from a spectrometer, and I want to have the option of with/without background subtraction.

And I set the array to be all 0 when I choose no background subtraction, then the final spectrum shows all 0.  

By monitoring the data, I found it is the 'minus' function that cause the result.  It returns an array with all 0 when subtracted the  background (all 0 values) from a signal (not all 0). 

I simulated the singal using random numbers (with code attached), but the idea is the same.

Can you help me find a solution on this?

Thanks

[Mark_Yedinak]

Your are using an array of size sero when you aren't subtracting the background. The array needs to be the same size. Better yet though would simply not do the subtraction when the background should not be removed.

[sxy248]

Hi Mark, 

Thanks for the reply. I am not familiar with LabVIEW.  How do I set the size of the array? By initialize?

I also want to ignore the background subtraction when it is not needed, but how can I bypass it?

Thanks

[Kevin_D]

To ignore the background subtraction, you can use a case structure. i.e. 'TRUE' = subtraction case, 'FALSE' = no subtraction case. 

[crossrulz]

Just use a case structure.

The False case only has the wire from the Signal tunnel to the Final Spectrum tunnel (passing straight through).

[altenbach]

Alternatively, you could build an array with zeroes instead of the random numbers.

Also:

• Your array building is better done using autoindexing (you also have a lot of type mismatches).
• Since your points are equally spaced in x, you don't need an xy graph and the associated more complex data structures. A plain waveform graph is sufficient.
• There is a primitive to take the mean of an array.

Maybe the attached can give you some ideas.

[sxy248]

Hi, 

Thank all of you guys, this is very helpful.