Re: Lambda sensors - Where, Why and how Much ?

[garwillis@msn.com (Garfield Willis)]

On Thu, 8 Jun 2000 08:35:29 -0700 (PDT), Squash <realsquash@yahoo.com>
wrote:

>--- Len Sabatine <sabatine@epix.net> wrote:
>> > > -- One of those wires goes to the Ho2s [ Heater ] One of the ground 
>> > wires is redundent.
>> 
>>          Len
>
>Then why did they put 2 ground wires in?

Good EE practice. The heater lines carry beau coup current, multiple
amps, you don't want any possible contact problems causing the reference
for your O2 sensor to levitate. Hence, use a separate "signal gnd" for
the smallish O2 sensor signal. You'll see this practice of separate
sensor reference gnds showing up moreNmore in automotive, as the signal
levels come down, and the noise margins become more an issue.

The hysteresis in the older one-wire O2 sensor circuits had to be set
much larger, AND some designs I've seen, the actual signal threshold
floats around, centered between the min & max O2 swings, just because
the gnd reference for those earlier sensors was potentially so poor and
floaty. Hey, it's now better design thru better wiring!

Gar