<VV> Tachometer

[Dennis & Debbie PLEAU]

I've got 3 dwell tachs, all analog and all give a slightly different 
reading.  I like the control of the local utility over the frequency.  I 
should use them to calibrate my test equipment, but it would still be an 
intermediate step to calibrating the tach and every step introduces error.

dp



>From: "Secular" <rusecular at yahoo.com>
>Reply-To: Secular <rusecular at yahoo.com>
>To: <VirtualVairs at corvair.org>
>Subject: Re: <VV> Tachometer
>Date: Thu, 1 Mar 2007 21:54:51 -0500
>
>
>   Why is this discussion missing the use of a dwell/rpm meter?
>   Why can't all this "chime my bell" not get substituted by an
>   Dwell/RPM meter - then making the adjustment on the tach
>   based on what the meter is showing?
>
>   hmmmm....
>
>   Tony I.
>
>
>----- Original Message -----
>From: "James Davis" <jld at wk.net>
>To: <VirtualVairs at corvair.org>
>Sent: Thursday, March 01, 2007 9:33 PM
>Subject: Re: <VV> Tachometer
>
>
> > This discussion is on how to adjust a working tach; not how to repair
> > a tach.  A signal generator would be ideal but Tony, Lew, Fred, and
> > Rad are probably the only Corvair people that have one.  Most of us
> > have AC electricity near when working on Corvairs.  Since power
> > companies spend millions keeping the frequency of AC perfectly stable
> > at 60 hz (cycles per second to you old ee's), why not use that
> > standard to calibrate the tach.  The tach wire in the coil is a handy
> > place to insert the frequency standard.  The problem is the tach is
> > looking for a 6 to 15 volt pulsed DC signal and the house current is
> > 117 volts, sine wave, AC.  Fortunately the tach has a zener diode in
> > the input which can change a sine wave AC to pulsed DC, so we just
> > need to drop the household voltage to the tach voltage.  A door bell
> > transformer changes 117 AC to 14 volts AC so it will work.  The
> > proper sized resistor in the probe will also work.  As for why 1,200
> > rpm?  Household voltage is 60 hz or cycles/sec.  That equates to
> > 3,600 cycles/min.  Since the there are three sparks per crank
> > revolution, divide 3 into 3,600 sparks to get (tada) 1,200 rpm ;-).
> > Jim Davis
> >
> >
> >
> >
> >
> > At 06:13 PM 3/1/2007, Mike Demeter wrote:
> >>I do have a tachometer that does not work.
> >>
> >>Explain the doorbell transformer?
> >>Explain the 60 hertz?
> >>
> >>Am I confused???
> >>
> >>Mike
> >
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