How does a tachometer work

[the hangman]

A freind is installing a tach in his older boat. The manufacturer says he needs a tach designed for a 20 pole alternator (Force motor). Why does a tach work different on an outboard vs an inboard engine?<br /><br />Jeff

 

[voodoo]

Re: How does a tachometer work

I believe the outboard measures the cycles of the ac then divides to get the rpm.<br />Most 4 strokes measure the # of times the coil is asked to fire, then calculates by the # of cylinders.

 

[rodbolt]

Re: How does a tachometer work

usually an analog tacc is of the a/c drag cup type of device. the cheaper ones use the ratio of voltage increase vs magnet speed the more expensive ones and most digital us an actual pulse counter . each time a fly wheel magnet passes a coil of wire it will generate one complete sine wave. the waves can be clipped,shaped and/or rectified as well as be converted from an analog signal to a digital pulse. if you dont have any training in electronics the look for clippers,clampers and wave shaping circuits on google and see what happens,<br /> good luck and keep posting

 

[Rudderman]

Re: How does a tachometer work

On my tach there is a little switch on the back that you can set for different pole settings