Inductive tachometer Tiny Tach, Sendec

Is members have some experience with the inductive tachometer like the Tiny Tach or the Sendec with the wire going around the cable spark plug?

 

Someone on another forum made mention of a non-contact laser tachometer, but they only work when the cowling is removed. I have no such experience but am also considering buying a tachometer.

 

Hoyt, I read the Sendec is only one wire going around the spark plug, the Tiny Tach as an other wire going to the engine ground.
I wounder how they work.

 

I am interested to learn also.

 

I have had two of them. One worked well on a Yamaha 4 stroke, but with my Tohatsu I can set it to under read (8 pulses) or over read (6 pulses) I cannot set it to 7 which is what is needed. Sorry I don't understand engines, so may have it back to front. But they do work. Also the hour meter is useful

Very cheap on ebay (USD10 or so), but I think those are Chinese copies

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Such tachometer designs emerged for the first time some 50 years ago. Because there is an extra amplifier stage needed for the weak signal, they are susceptible to electrical "noise", making the wiring critical. A long wire length may require a shielded cable.

Using the ignition coil or the stop switch as a signal source is much easier and reliable.

 

Would regular coaxial cable(like for TV) work?

 

Certainly Hoyt.

 

Thanks.

 

For this connection it will be for a classic electronic tachometer or still a inductive tachometer?

 

Classic tachometer circuits have a relatively low impedance (5-20 K-Ohms) with a protection circuit to suppress the 200+ flyback voltage from the coil.
The inductive ones have a much higher impedance because otherwise the signal collapses. I have also seen tachometers with a number of dip switches at the back to select 2/4 stroke, number of cylinders AND the input source.