More DIY EGOR

[RDwoo10 at aol.com]

I guess that i am making too many assumptions.  one is that the temp that the 
heater is going to control the sensor to is higher than that of the possible 
temp that the exhaust gasses are going to heat the sensor (so there is not an 
issue of "sinking" heat, where we would have to cool the sensor to maintain 
the set point).  this is where the "10% above the temp sensor w/exhaust 
gasses alone", thing came from.  

When you mentioned the addition of a TC i assumed @ the sensor tip or some 
relatively similar point.  I did not see any advantage (still don't but, I 
think that I am still missing your point on this) of having a sensor outside 
of the environment.  

Another assumption was that this being an analog control circuit, the control 
is always going to be one step behind the temp.  w/a digital signal we can 
use a PID loop & predict the needed drive to maintain temp, but w/analog you 
have to play catch up, or run the risk of oscillation or wild overshoot.  

i did not consider the warm up of the sensor to be an issue.  i would imagine 
that the warm up time on the sensor is going to be fast enough that there is 
not going to be an issue with the response of the sensor, that is going to 
affect anything other than warm-up characteristics of the engine, annoying as 
it is to sort out.  that is to say that i am guessing that the sensor is 
going to get to temp way before the motor does, & certainly before it gets 
into closed loop (where i would ultimately like to take this)  There is the 
real possibility of hurting the sensor (as you & Bruce pointed out) but i 
would imagine that there ought to be current limiting, that is going to take 
care of that.  if the temp is controlled digitally the PID can control the on 
time when the temp of the sensor is @ the bottom end (low resistance/high 
current).  

if i might, lets take a step back.  the reference (the big picture here), is 
the Motec & the Horiba & the other big $ units.  they use the same sensor do 
they not?  if that is the case then i would think that they must be using 
some similar scheme to control temp & that this ought not be an issue.  is 
there a concern that this is going to be an issue or is this just a thought 
that is getting chased down?  

Personally I would prefer to eliminate as many variables as possible.  If 
there is another temp sensor (chips, caps, resistors, etc.) there is an issue 
of unit to unit variation (as if there is not enough already).  This from 
what I understand from reading the threads on the WBO2 for the FelPro system 
& the Disk & the resistor etc., this sounds to me like multi layered 
complexity. 

what i am hoping to do is to chase down & simplify as much as possible.  my 
vision, as convoluted as it may be @ 11:40 PM on a Thursday night is to use a 
basic stamp (or basic X or similar) & as little analog as possible to make 
this thing sing.  i think that an open air, @ temp, calibration is a good 
idea & would help to eliminate the unit to unit variation.  I think that this 
ought to be simple, the burning question is, what about the other end.  air 
is pretty reliable for a span gas but what about a zero.  i have access to N2 
(& other gasses) but that does nothing for me here @ home (or on the car).  i 
can make a jig & take it to work to characterize a "bunch" of them & hope 
that span is good enough & that zero will not be an issue.  If that is the 
case then all is good.  If not then, what is a hot rodder to do, but to drop 
back & fall on plan B.  i guess then @ that point I would actually have to 
come up with a plan B.

SO, bottom line, is there a temp issue?  I would not think so, but w/o having 
actually put the circuit together & whack it w/some heat, who knows.  As you 
mentioned, the easy thing is to maintain the temp of a chunk of metal & 
ceramic.  Now put it into an exhaust stream & see what happens.  

Enjoy what is left of your day.

BW
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