Eliminating noise while analog voltage source idle

[ahsan2]

Hi,

I am measuring the analog voltage signal of an Omega FLR-1600A flow meter using a USB-6009. The flow meter has a 0-5 VDC output signal that corresponds to 0-1 LPM (liters per minute). The problem I'm having is that while the flow meter is reading zero flow, I'm getting a noisy signal that fluctuates between 0 and 0.1. Otherwise, the signal is clean and accurate. Here is my front panel and block diagram:

Is there a way I can eliminate the noisy signal such that the graph reads zero while the flow is idle, even if done artificially?

Thanks

[crossrulz]

It could just be your flow meter.  Have you tried looking at the signal with an osciloscope?

[ahsan2]

I have not looked at the signal with an oscilloscope. However, there aren't any controls on the flow meter that allow me to alter the signal in any way. Are you suggesting I do something about the signal before it's read by the DAQ? I was looking for a way of replacing the noisy signal with a flat zero line on Labview.

[RavensFan]

Run that signal through an FFT, see if there are any higher frequency components, perhaps 60 Hz line noise?

You might be able to filter your signal to reduce the noise.

[crossrulz]

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ahsan2 wrote:  Are you suggesting I do something about the signal before it's read by the DAQ? I was looking for a way of replacing the noisy signal with a flat zero line on Labview.

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I was suggesting that if you have no flow, then the meter is just measuring noise.  And you therefore get noise out of the 5V output.  I'm basically trying to isolate whether that noise issue is on the DAQ side or the meter side.  You can start to play around with things from there.

But RavensFan is pointing to what I am suspecting with 60Hz line noise coming from the AC power.  You could do a simple digital filter to try to reduce that noise.

[Bob_Y.]

I think what you are looking for is to show a signal that is smoother than the real one. Try the in-range and coerse and set the lower threshold to 0.03 or so. Then use a select and if the coersion output of the in range and coerse is true, set the value to 0 otherwise, use the output. 

You could also just use a less than instead of the in range and coersion, but I prefer it so that I can more easily search for it. 

Hope that this helps