How to measure electrical frequency?

[killjoy_scofiel]

in f to V converter, input is frequencies . Is that electrical or Mechanical frequency?

 

[dlgoff]

To convert a frequency to a voltage, you need an electronic frequency (voltage varying in time).
One can use different types of transducers to get an electronic frequency from a mechanical one.
National makes a chip, LM2917, just for this application. Check out http://www.national.com/mpf/LM/LM2917.html" where you can see the transducer (magnetic pick up).

 

[killjoy_scofiel]

sensor transduces electrical frequencies?
how to convert this frequency to mechanical frequency(RPM),,,
i ve seen a design before, they use scmitt's trigger before f to V converter

generator--->trafo---->scmitt's---->LM2917---->PLC---->inTouchwonderware

i think schmitts don't sense the frequency...(no magnetic pick up)?

LM2917 only detect positive peak of sinusoidal wave?
http://www.imagehosting.com/out.php/i1447796_all.jpg