DIY_EFI Digest V5 #390

Chad Clendening clendenc at execpc.com
Tue Nov 21 01:46:46 GMT 2000


UEGO answers:

1) The collector of Q3 should be connected to the V-2.5 referance.  Sorry, the second
soldered proto was build directly from this but after knowing the circuit that type of
thing can be easily overlooked.

These 2 transistors are needed as the op amp had difficulty providing enough current.
It would get too close to the power rails and go flat.

2) Heater operation:

The thing limits voltage so
    A) current is below specified value and
    B) limits voltage to a limit.

Which causes 2 power modes, P = i ^2 R
                                         and P = V^2 / R
The R is the resistance of the heater and is a positive temperature coefficient.

so the power dissipated increases with temperature untill it is warm.
Once warm, power increases as it gets colder and decreases as it gets warmer.  This
causes it to be somewhat "self reguating".

On some of the other UEGO's,

These are bits I have heard, I don't know the accuracy of them.

The 4 wire ND UEGO is a negative temp coefficient so that takes a very controlled
power supply.
They also are in use on some newer GM cars.
The accuracy isn't as good as the NTK but fine for automotive purposes.


I really don't think the UEGO heater requires a seperate ground from the body.  For
years, the 3 wire HEGO sensor had a seperate ground for the heater and used the engine
block as the ground for the Vs Cell.  It doesn't make any sense from an operational
standpoint, why is the analog signal tied into the noise engine ground?  Why is the
heater given it's own ground when all it gets is a V+12 applied ?

If  ND ran the heater ground through the body, then the Vs And Ip cells would have a
common ground.  It is still annoying that the corporate bean counters axed the
seperate ground wire for the 2 cells.  That would get UEGO functionality out of 4
wires.

Chad





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