[Diy_efi] Re: MegaWideband digital WBO2

[Perry Harrington]

> Not in the 210. My firewall address is 203.59.*.*

Upstream.

> That'd be better. A less "global" blocking of IPs is probably
> desirable.  Using SPEWS or other similar is an option if you don't
> want to maintain your own blocking list.

Using ORDB now; open relay database.

> 
> Now... back to the topic; you are aware that the apparent
> resistance of the pump cell will change with temperature?
> That will change the current that actually flows through it will
> vary. The EMF presented by the pump cell will vary depending on the
> difference in EGO in the exhaust stream and the measurement cavity.

So the bias current required to compensate the Vs will vary with temp?
Just like the heater, correct?  Can we assume that the cell temps
are the same as the heater temp?  The design is very critical of the
Heater temp.  The schematic will be redesigned to put the sense
resistor on the ground of the FET and simply sense the voltage directly
there.  The design measures the impedance of the Heater in realtime,
controlling the current to the sensor in order to keep the heater at
800C.  I assume 800C is the target temp?  According to the figures
on the DIYWB schematic, the target impedance is 9.7ohms for 800c.
Plugging that into this formula:

    (input V+ - senseR voltage drop)
Z =  --------------------------- X senseR ohms
        senseR voltage drop

To simplfy for our needs:

senseR voltage drop = V+ / (Z + 1)

.966 = 10.34 / (9.7 + 1)

So my initial calculation was incorrect, the sense resistor should measure
a voltage drop of .966v when the heater is at 800C.

So, if we know the cell temp, then we know what amount of current is
required to bias the pump in order for Vs to equal 450mv?

The temp bias would cancel out, since we try to regulate the temp tightly.
Am I missing something here?

BTW, if you have a look at the design I did away with the switched polarity
H-bridge that you are using.  Instead I offset ground and switch the high
side, this gives 2.5v cell voltage and requires less components.  The mCU
can sink 20ma on the PWM lines, so no external logic is required.

I think I will add a relay to simultaneously switch the Vs/Ip ground and
enable, this way I don't have to compensate for voltage drop and there
is no possibility of engaging the Ip pump if the chip is wedged.

There is a separate enable which will control the Ip current as well as
provide a true ground reference while the heater is warming up.  The Ip
pump will turn on 10 seconds after the Vs drops below 1.1v AND the Heater
is in regulation mode.

Further modifications may see a 12v quick heat mode to get the heater to
operating temp quicker.

> 
> See the bibliography on my DDL project page

I didn't see a bibliography.

> 	http://bernd.felsche.org/tech/EFI/DDL/DDL.html
> 

--Perry

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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