I am looking to measure the rpm of a wind turbine, the wind turbine is 3-phase synchronous generator, the frequency range I am looking to detect is between 1Hz to 60Hz, I tried to use a frequency meter with 0-10v analog output, but it doesn't pick low frequencies and keeps freezing or even give random wrong results when the frequency changes rapidly.
Hello shamooooot
Measure the time interval between the two rising edges and derive the frequency.
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thank you for your input.
I am looking for something automated to do that as I need to acquire the value of rpm to a Data acquisition and a display..
An Arduino would provide a propper base for a clever solution.
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Can you elaborate please ?
Sorry.
You have the key user requirments for your project.
What is the source of the frequency signal? The AC output, hall sensor, opto sensor?
it's the ac signal phase to phase from the generator
So, lets speed things up here. We can sit here all day long, qeustions and answers fly by and not getting anywhere somehow.
A circuit diagram, attach one to your first post. This should include the single components / modules along with model numbers, how they are wired, links to datasheet is also good. Moreover you should put voltages and other variables, like you already specified the freq.counters voltage output - 
This will get things started, and welcome to the forum!
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I don't know what a synchronous generator is, but you ONLY need to look at ONE SINGLE PHASE to determine the frequency. Just detect the zero crossing time difference between any two zero crossings of that voltage of that phase.
Are you sure this is a "synchronous generator"?
Synchronous requires an external source of timing information. Why not provide some actually useful details, like a link to the thing?
Yes 100% sure it is a Chinese wind turbine that is 12v and is Three-phase AC permanent magnet synchronous generator..
Here is a schematic for an attempt I made, I pulled two wires from two phases and connected them to transformer to step voltage up, then I fed them to frequency counter. The device couldn't cope with the very low frequency I believe.
Just use an Arduino ADC to monitor the signal, with a voltage divider and offset to keep the voltage within bounds. See CT Sensors - Interfacing with an Arduino — OpenEnergyMonitor 0.0.1 documentation
The Chinese may advertise that as a "synchronous generator", but it is not.
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Yes I tried several methods including turning the AC signal into an analog through a precision rectifiers but I think either the voltage was too low or the frequency was too low and the Arduino gave crazy high results, even though the code works when logging other analog signals..
You need some kind of pulse generator like Hall effect sensor and small magnet(s) on the turbine. Must be weather proof though.
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I am afraid the current is too low to be stepped down further..
Would be the easiest way. And non intrusive.
That doesn't make any sense. The ADC reads the voltage, not the current, but the voltage must be reduced to be within the ADC range.
Problem with permanent magnet generator is low RPM means low voltage, no way around it. You can use your method on a car alternator but a car alternator always runs at least 1500 RPM even at engine idle.
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