More DIY EGOR

[Bob]

A little over a year ago I was considering purchasing an NGK wide band
sensor package (sensor, cable, and controller). I had the opportunity to
speak to an NGK engineering manager and the subject of cable length (between
sensor and controller) came up. He said that the NGK sensor package would
only function properly if the cable shipped with the package was used.
Maintaining the correct temperature at the sensor was critical and that any
change to the cable length (just copper wires) would seriously compromise
the controllers ability to maintain the sensors temperature. They used the
heating element to sense the temperature.

Bob K.

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of RDwoo10 at aol.com
Sent: Friday, November 17, 2000 2:44 AM
To: diy_efi at diy-efi.org
Subject: Re: More DIY EGOR


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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