Keeping Power Spectrum Peaks on a Graph

[needtolearnfast]

Hello,

I am trying to read in a signal which varies in frequency as time progresses. I am taking this function and running a real time power spectrum (FFT Power Spectrum.vi) on it. As time goes the peaks move around according to teh frequency which is coming in. What I want to do is to keep the old peaks on the graph as the new peaks come in. So for example if I had a signal which was at 50 htz then 75 htz, at the end of the run I want to see both peaks on my grpah. Is this possible? Thanks.

[tbob]

If you use the Spectral Measurements Express VI, you can configure it to do peak hold. In the configuration screen, turn averaging on, click on the Peak Hold radio button, and set the averaging number to 1. Then all your peaks will be displayed as they come and go. See attached vi. If you want to see how the express vi does it, you can convert the express vi to a normal vi and then look into the block diagram. I believe one of the functions has a peak hold input.