Underhood Temperatures

[bernie at innovative.iinet.net.au]

Garfield Willis tapped away at the keyboard with:

> On Fri, 26 May 2000 10:15:57 +0800 (WST), bernie at innovative.iinet.net.au
> wrote:

> >You change the system in order to observe how it performs. 
> >All you'll onserve is how the changed system performs. Or
> >don't the temp sticks have any physical properties at all?
> >
> >If I crack open a chip and paint the surface with the pen then try
> >to observe the temperature - I'll probably get very misleading
> >results in relation to a practical application.

> Non sequitur, dood. If you paint a swipe of T-stick across the chip
> surface and then heat it up, you can DEFINITELY tell if it's reached the
> T-stick temp or not. Your example of cracking open a chip is way off
> point. Something's cracked alright, but it's not the chip.

I'm talking about the self-heating of the chip under nominal
operating conditions and the consequences of changing the system in
order to observe it. Sorry if you didn't get the point.

> >The Heisenberg principle applies to all systems which are observed.
> >It's an early awareness of chaos.

> The chaos... I can see that. None of the above amounts to anything of
> consequence in the real world we've been discussing. The T-sticks are
> like crayons; you're tellin us we ought to worry about the heat effects
> of a swipe of crayon on some object inside the engine compartment. Get
> real.

I apologize for the pendantism. It's a habit of getting designs down
to within the last percent or less.

> >A couple of seconds to a minute more likely; on my engine a couple
> >of minutes makes a world of difference to the inlet manifold (which
> >is directly above the exhaust manifold).

> OK, in your case don't mount any electronics near your intake manifold,
> cuz it's near your exhaust manifold. Simple, huh?

Problem is; I almost certainly want to; in order to measure the
precise time of pressure pulses in the inlet tracts above the valve.
The transducers need to be as close as possible to reduce the delays
and the effects of compressability.  The reasons for which will be
explained after I can get these stupid bits of software out the
door and get some time to practice my hobby.

> >The relative temperature changes are most significant and depend
> >hugely on engine layout and the operation of ancillaries. (Electric
> >cooling fan.)

> >You might get more time with a mechanical cooling fan.

> When you shoot underhood temps with a gun, you don't have EITHER fan
> running. You shut down, let soak or no, then open the hood and start
> probing. Other than thin metal baffles and the like, everything else

The fan often starts at a psuedo-random time after the engine
has been shut down. That's the result of heat transfer in the
cooling system and a characteristic of the thermoswitch.

> VERY slowly coasts down. Changes in just a few seconds you just don't
> see; sorry, it just doesn't square with practice.

I wasn't arguing about a few seconds. I'm well aware of thermal
mass.

> >Yeah... pretty neat gadgets. I saw one which had a laser pointer but
> >the sales guy couldn't verify that the laser spot was even pointing
> >at the spot being measured. I didn't even ask about the power output
> >of the laser. :-)

> Good idea, you'd have had to wonder about how much heat the laser
> pointer put into the thing your measuring then, huh? Ever try it on your

No... I wasn't really wondering about the laser power output as I
wouldn't be using it to measure the temperature of sensitive stuff
such as undeveloped photographic film.

> hand? Heh. Besides, I'd never look to a sales guy for my technical
> understanding anyway. The typical way to align the beam is to use a very
> hot point source, like the end of a hot metal rod, and scan the area to
> peak; the beam should be pointing at the hot point source. Quite
> practical and repeatable.

Well, you know about it; but when you're trying to get the price
down on one of those gadgets, you need to cut the sales droid down
to size for a better deal - which never got good enough. If the guy
wants a couple of months' worth of "spare cash" for what is at best
(for me) a toy, then I make him work for it by gaining product
knowledge.

(I'd use a soldering iron; end-on. 300C or thereabouts.)

-- 
Bernd Felsche - Innovative Reckoning
Perth, Western Australia
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