Can not measure frequency

[ASIAN INSTITUE]

Hi,,

I want to measure the RPM ( rotation per min ) of a roller by using photomicrosensor of Omron. The output of the sensor should be pulse waveform. If I could measure the frequecy of the waveform , I will know RPM.

However, the pulse waveform I got that has noise thus i did compare the waveform applitude ( Voltage ) with constant value in order to cut the noise, then rebuit the new waveform that its waveform voltage is real pulse.

But I can not measure the frequency althought I used some tool such as Tone Measurement...

The attached file below is my program.

Please help me .

[AnalogKid2DigitalMan]

What DAQ card are you using? If it has counter/timer I/O, I would suggest squaring up your Omron output to TTL (0-5V) levels and feeding that into a counter. There are examples that ship with LV to measure frequency- search Help to find them.

[EdDickens]

To easily measure the frequency of a pulse waveform, you should try using a Counter on your DAQ card instead of an analog input.

The counter will give a much more accurate frequency reading and even have the ability to filter noise. You'll still have to use the analog inputs if you want to display the waveform on the front panel, but I think you'll have much better luck getting the frequency using a counter.

Check out the Counter examples that ship with LabVIEW to get started.

Ed

[LV_Pro]

I agree with Ed, and will also mention that the counter use an accurate timebase, which will give more accurate time measurements than any LabVIEW based loop.