Standard tachometer Hookup?

[linhster]

I created a custom LED dash and trying to get all the correct sensors signal to feed the instrument gauges. The tachometer is the current task at hand. I ran a line from the AC terminal point of the 200amp Gen/Alt. The reading seem very high at idle (1800 rpm). Can I get some assistance with the detail of output signal from the alt to make the adjustment. Maybe the signal count is higher than the traditional 8 cylinder count???


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[mechanicjim]

On the Niehoff alts the AC terminal is one half System voltage AC Sine wave.
so on your 200amp it would be a 14v AC signal. with a DVOM that has a Frequency/HZ function you can take a reading from the AC terminal to get the RPM of the Alternator. in normal Diesel setups Alternator RPM is a 3:1 ratio to engine speed. so ALT RPM 2100, engine RPM 700 roughly.
Now the things that can affect this reading most are belt pulley ratios.