[Diy_efi] uego ground (nernst and pump)

Bernd Felsche bernie at innovative.iinet.net.au
Thu Feb 27 23:40:15 GMT 2003


On Thu, Feb 27, 2003 at 02:12:38PM -0800, Stewart Prince wrote:
> We're looking into closed loop fuel control on our FSAE car using
> the NTK uego.  A student has an interesting idea, similar to  the
> direct digital lambda technique, but he wants to use an H-bridge
> directly across the pump cell.  This means the ground side of the
> pump cell would possibly have both positive and negative voltages.

No problem. H-bridge was the original concept for DDL.

> We know the other side of the pump cell can have negative voltages
> as this is how current is pumped out of the cell.  The real
> question becomes:  Does the nernst cell have to be grounded to the
> pump cell directly?  Can they have separate grounds?  The nernst

AFAICT, the sensor's construction, both NTK and Bosch, has a common
junction in the substrate for the Nernst and pump cells.

> cell must have a continuous ground as it is used as a reference
> for its output voltage, although it can be an isolated ground.  I

The Nernst cell voltage will float above whatever is it's has as
it's "ground". Applying a reverse bias voltage on the pump cell,
which has one common point with the Nernst cell, and the Nernst
cell's output voltage will increase correspondingly.

To detect Nerst cell switching "above" (or voltage), measure the
voltage relative to it's virtual ground.

> have never measured the internal resistance between the two cell
> references.  

-- 
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