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How can I measure RPM with CTR-500 module?

I have used  the CTR-500 module for mesurement of  motor RPM. But it doesn't have direct option to measure  RPM ,
so i have count pulses for  1sec (then reset the counter) and  by calculation show the result for 1min. But it varies every time ,cant give me fix RPM.
I want reliable solution for this.
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min

You have not said how much the RPM actually varies from reading to reading and what the range of measured RPM is for the process.  This variation can be caused by a couple of things.  One would be actual variations in RPM due to changes in motor loading.  What is this motor driving?  Most RPM readouts use some form of sample averaging to smooth out the readings.

A second cause could be your vi.  Suggest you post a copy of your vi. 

In case you have not seen it, here is a link to a KB about measuring frequency with cFP.  It also links to several other docs on the same subject .  http://digital.ni.com/public.nsf/allkb/D8DB42F9FDC3607E862568640047F144?OpenDocument 

 

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