<VV> Thermister Swap?

[Jim Simpson]

Bob, excellent question regarding the supply voltage.  I was using an HP
variable supply, set at 13.8 volts approximately.

I did wonder about the sensitivity of the gauge to supply voltage and found
that the readings didn't change over a very wide range.  I went as low as
about 8 volts and a bit over 14 with no observable change in the needle
position.

That said, I didn't check over the full range of the gauge, nor did I check
more than two gauges.

But this appears to be an area that GM got right.  They used bi-coil (two
coil) meter movements.  These are specifically designed to be insensitive
to supply voltage.  From the limited information I can find on this design,
they use two coils that essentially balance one another.  As long as the
current changes in both coils in the same ratio, the needle doesn't move.
One characteristic of this meter design is that when you turn off power,
the needle doesn't go to zero; it just sits there.

Jim Simpson
Group Corvair


On Sun, Sep 7, 2014 at 11:15 PM, <BobHelt at aol.com> wrote:

>  Jim,
> What supply voltage did you use for your measurements?
> Bob Helt
>
>  In a message dated 9/7/2014 6:03:10 P.M. US Mountain Standard Time,
> virtualvairs at corvair.org writes:
>
> I was shocked by my results!  If Mr. Berkman's data are correct, the stock
> Corsa setup is about correct at only 200 degs F cylinder head temp.  After
> that, it reads progressively LOW.  Based upon my measurements of the gauge
> response and Mr. Berkman's data, I'd estimate that at a real head temp of
> 500 F, the Corsa gauge is indicating about 350 F.  That's a scary error!
> I'd rather it read too high than too low!  Basically the stock Corsa gauge
> and the AC/Delco thermistor don't match each.
>
>