O2 sensor response times

[Gary Peyton]

First, let me say that I'm a complete novice in here bumping around trying
to learn enough about EFI to play around with/modify/replace the unit on my
Datsun 280ZX, so this may be a stupid question....

I had read somewhere that the response time of the platinized zirconia
sensors was 2-3 seconds, and that was one reason why they werent very good
for close engine management during acceleration (along with the way the
L-jetronic system used that information).  If a sensor like the LAF O2-pump
type sensor employs 2 of these, how can its reponse time be any better?
Maybe I'm suffering under a misconception here, since the www.tech2tech.net
discussion says that "A good O2 sensor will usually module several cycles
per second.". Are they referring to a simple one-wire zirconia sensor?
Please correct my thinking, because I'm here to learn, and starting to
think about buying parts to play with.

Thanks,

Gary Peyton  


At 12:47 PM 03/27/2000 -0800, you wrote:
>On Mon, 27 Mar 2000 07:32:21 -0700, bearbvd at cmn.net (Greg Hermann)
>wrote:
>
>>On Mon, 27 Mar 2000 14:26:30 +0100, Corner Paul <Paul.Corner at icl.com>
>>wrote:
>>
>>>> This has probably been asked before - but as I can't access the archives
>>>> at the moment, so...
>>>> what is the typical response time for these lambda sensors ?
>
>>One of the NTK WBO2 pump type sensors is generally capable of picking up a
>>misfire on a V-8 at 3000 rpm---so pretty quick for these!
>
>This is an interesting question.
>
>As Dr. Pelican and Greg have mentioned (in the original NTK article,
>they give these same numbers for misfire detection on an I-4), there are
>some "varying claims". If you add in the high-end meter mfg's specs for
>response time (I remember seeing one claim 0.05secs!; ECM Inc says their
>NTK-based boxe$ response time is "<150ms", while curiously NTK doesn't
>spec the response time of their own blue box system/interface), so
>you've got all kinds of all-over-the-place specs. Even in the NTK
>article, there seem to be potentially conflicting numbers; in one place,
>they show the response time for AFR deltas/excursions of around +-4AFR,
>and show these response times in the several hundreds of milliseconds!
>Then, in discussing the ability to detect misfires (seeing the lean
>excursion that occurs from one cyl's mix not burning), they show blips
>in the sensor's outputs that are as narrow as say <100ms, and conclude
>from that "...by using the lean signal [the lean excursion blips I
>mentioned prior] with the ign timing signal, the misfired cylinder also
>can be distinquished". How this all corresponds to picking out misfires
>at 3-4kRpm I'm still unclear on. The numbers just don't seem to match
>up. Add to this, the diagram they (NTK) give for their misfire test
>setup shows all four exhausts collected and then the AFR being measured
>*downstream* just prior to the cat. Thus, there is definitely some gas
>mixing. Remember that mass transport (exh gas movement) occurs at a much
>slower speed than pressure wave propagation, so just because the exhaust
>puffs indeed have a distinct and sharp delineation in pressure, gotta
>consider that in a manner akin to waves propagating in the ocean, the
>pressure phenom may be very distinct along with considerable
>mixing/diffusion of the mass of the media taking place as it transports
>downstream. As an extreme example of this phenom, consider the flow at
>the end of the tailpipe, where even tho the pressure pulses from each
>cylinder are still clearly distinct, the individual mixture packets from
>each cylinder are by then pretty thoroughly mixed/averaged.
>
>Having given all those caveats, what seems to be universally accepted is
>that these sensors are indeed noticeably faster than say the older HEGOs
>like the LSM-11s (Frank Parker showed me an example where his NTK box
>caught a funny rich blip/excursion on his Typhoon when you quickly
>released the throt, but IIRC, his LSM-based equipment misses that
>excursion...correct me if I err here FP). And what's probably most
>important, they DO seem to be fast enough to catch any possible mixture
>excursions that present EFI controllers can produce. Hardly a "spec",
>but reassuring nevertheless. We just haven't had time to set up an
>apparatus to do our own response time testing, but I can tell you that
>EGOR does absolutely NO smoothing or averaging of the sensor output, so
>whatever the bandwidth of the sensor itself is, you're getting/seeing
>all of it at the output of our electrics. I have no way of knowing if
>this is true for other mfgs.
>
>If I had to guess from the mongrel mix of specs, the response time is
>probably somewhere between 100-200ms. Just a swag, tho.
>
>Gar
>
>
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======================================================================
Gary R. Peyton
Senior Professional Scientist
Watershed Science Section
Illinois State Water Survey
Illinois Department of Natural Resources
(217) 333-5905	FAX (217) 333-6540
===================================================================

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