has anyone tried this, i think this it will work just want to get some opinions, can you measure the rpms by using a digital volt meter set to alternating current and ground the negative side and put the positive side to the tach wire, it seems like it would work, but might need an equation to figure it out, i dont want to fry my brand new $89.99 digital vom.

 

Tach triggers are typically a square wave, not sinusoidal.

 

Yup... but that's not why it won't work.

The problem is, that the amplitude of the square wave doesn't change as RPM changes; only its frequency changes. Soi the DMM will read pretty much the same thing no matter what the RPM is.

If you had a frequency counter with an appropriate filtering network in front of it, then that would of course work. Another name for that setup is "tachometer".

 

You are correct. At the time I posted, my mind was in neutral.

 

They make dvom's that can display rpm and dwell.

 

i have a mt500 from snap on the does dwell and rpm among other things as well as a DVM i'd like to sell. not used it in a very long time. i have a fluke 88 that does all the DVM stuff plus temp, rpm, dwell, etc for engines.

 

equus makes a timing light that displays rpm... i'm sure there's other things it displays as well.

i know actron makes a dvom that can measure duty cycle, rpm, dwell and a bunch of other features...