Measuring frequency from an analog signal and reducing noise

[lukepike]

The sensor is an FT-110 TurboFlow from Gems Sensors (Part number 173934). The spec sheet says the output is a NPN Sinking Open Collector @ 50mA max. The sensor does need power, 5 - 24 VDC with an external pull-up resistor (1 - 2.2 KOhm) to insure that the open collector will sink less than 50 mA (getting this from the spec sheet). You're right, there probably shouldn't be any pulses without flow. Here is the wiring diagram for the sensor.

Here's a link to the data sheet (it looks like a few things are different from the paper one I have, but should be good): http://www.gemssensors.com/uploadedfiles/literature/spec_sheets/FT110.pdf.

[lukepike]

Sorry about the double post! My browser lost connection and I thought I'd lost it. Can someone delete the duplicate? 

[lukepike]

The guys where I work have installed shielded cabling, and boy what a difference! There is now hardly any signal when there is no flow, less then 0.03 Volts. Coq rouge, thanks for the frequency example, It works very well!

Now I just have to see how it all works with actual flow. Thanks everyone for helping me out!