More DIY EGOR

[Bruce Plecan]

Maybe for a lab grade, in which case who cares..
Getting to be an exercise in preciseness that then useability
Bruce



> 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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