[Diy_efi] Bernd: UEGO sensor question

[Bernd Felsche]

bcroe at juno.com tapped away at the keyboard with:

> The Vs output is like a battery, a very low current one.  If 
> it were a variable resistance, the pull up or pull down 
> resistor value would be critical (which it is not) like the 
> pullup on a water temp thermistor.  

That makes sense... I've been trying to model it as a voltage source
at the core and it doesn't hang together in terms of response under
various scenarios.

If the cell is modelled as a small current source (variable, as it
depends on the ratio of partial pressures of oxygen) and a series
resistor (temperature dependent) then that explains the voltage
behaviour under "load".

Add a small capacitor in parallel with the current source and one
can approximate the behaviour when the cell is "exercised" by
external, possibly-alternating voltages.

A physical model, to perhaps use as a "simulator", may be more
difficult; the amount of current generated is miniscule; in the
range of low micro- if not nano-Amps.

-- 
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