EGT for mixture setting

[Andrew Dalgleish]

On Wednesday, 13 March 1996 12:14, owner-diy_efi-outgoing wrote:
> On Tue, 12 Mar 1996 wmcgonegal at rr.etc.ncr.doe.ca wrote:
> > It is not overly difficult to construct a thermocouple conditioning   
circuit.
> > One only needs an amplifier and a cold junction compensation circuit.   
 You
> can
> > even do away with the compensation if your circuit is always at the   
same
> > temperature.
>
> Is it practical to, put the cold junction into a lot of insulation, eg
> shove it into a giant block of polystyrene foam , or in a thermos
> bottle(?) and tuck it under the dash somewhere? in the extremes of heat
> and cold it may help to measure the temp of the juction with a   
thermistor,
> to compensate for the possible change in temperature.

I have seen this done using a thermos full of iced water. The trouble is   
the ice melts.
I guess it would be ok for short periods of time, like drag racing.

You could use solid state cooling, but that's fairly expensive.

Another possibility is to heat your cold junction (e.g. with a power   
transistor) to a *known* temperature
which is hotter than ambient, but less than the hot junction temperature.   
You have to contend with the
chicken and egg here. How do you measure the cold junction temperature in   
order to regulate it?

I guess the real question is how much will this improve the measurement   
accuracy over just using
ambient?

>
>                  Bruno.     ( u933234 at student.canberra.edu.au )
>
>                       "If you've gotta go, go with a smile"
>
>

Regards,
Andrew Dalgleish
Senior Software Engineer
Axon Research, Pty Ltd
6 Wallace Ave,
Toorak, VIC
3142
AUSTRALIA
Tel +61-3-9826-5538
Fax +61-3-9824-0083