Filtering for beginners... where to start

[Mike Whitaker]

I'm trying to work out where to start with filtering a signal. As I'm new to this field this seems to be a bit of a challenge at the moment. (something tells me that the challenges are going to bigger as I get further into this...)

I'm reading a signal from simlpe Reed switch in through a USB 6008 device. I'm looking to try and read the frequency of the pulses, however appear to be reading the frequency of the noise and not the pulses. Some bits of this make sense & I can see the signal.

The noise appears to be at about 900 Hertz & below .005 volts. I'm only interested in readings of 2.5 volts that will be around 20 hertz.

What is the recommended way of doing this? Should I be filtering out the higher range of the frequency or the lower range of the voltages?

Any advice of recommended reading on this would be appreciated.

Cheers,

Mike

[BillMe]

Can you post your code to show what method your using now? Under the Signal Processing palette (if you have it), there are waveform measurements that include pulse measurements that might meet your needs.

[Mike Whitaker]

VI attached.

Any comments appreciated.

Cheers,

Mike

[BillMe]

If you're interested in only the signal at 20Hz, you should change the Filter Express VI to a lowpass filter and the cutoff should be something above 20Hz, say 50Hz. Looks like you're setup for a highpass filter with the frequency at 0.0005Hz, basically passing all frequencies.

Hope that helps.