[Diy_efi] Re: uego ground (nernst and pump)
Stewart Prince
sprince at csun.edu
Fri Feb 28 00:36:11 GMT 2003
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Yes, I see this now. If the reference for both cells are tied together
internally, the best way do to it would be to reference ground signal to
2.5 volts. This makes an H-bridge unnecessary as any buffer with 0-5
volt DC output can drive 5mamp, easily. Thus, a PWM signal with a 50%
duty cycle would equate to Ipump=0 (on average) and with the proper
selection of a series resistor, a 100% duty cycle would equate to
whatever positive pumping current is needed, depending on what Air-fuel
ratio you want to calibrate to, and a 0% duty cycle will equate to a
negative pumping current.
One could size the op amp gain and the in-line resistor to yield the
proper max pump current at 100% duty cycle, but how does one know if the
pump current has really driven the nernst cell voltage back to .45
volts? I haven't modeled this system, but I'm assuming that it is a
type "0" system in terms of transient response, meaning there will be
steady state error. If you close the loop (the purpose of the op amp)
you will need a high gain to minimize the error, and this might create
"overshoot" and "ringing" of the circuit response. Perhaps what you
really need is to take the nernst cell signal, process it using a PID
algorithm, then send it out to the pump cell using PWM. This sounds
like a perfect fit for a microprocessor. I believe this is the path we
will take.
Many thanks
S. Prince
Klaus Allmendinger wrote:
>Hi,
>
>The pump cell and the nernst cell in uego sensors are physically bonded
>together. The common junction between the two is what you refer as
>'ground'. There is no way to separate them because they are connected
>together internally in the sensor and only one wire comes out. The same is
>true for other manufacturers wb sensors. A H-bridge design would require a
>differential amplifier that outputs the difference between nernst+ voltage
>and common ground. The difference then can be referenced to circuit ground.
>In my experience a H-bridge is not neccessary because in normal operation
>the required voltage to drive the appropriate current in/out of the pump
>cell never exceeds about +- 2V. This means that a 0-5V digital signal can
>drive the cell if the pump/nernst cell common is held at 2.5V.
>
>Regards,
>Klaus
>
>
>
>Regards,
>Klaus
>
>
>At 02:12 PM 2/27/03 -0800, you 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. 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
>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 have never
>measured the internal resistance between the two cell references.
>
>
>>STEWART PRINCE
>>
>>PROFESSOR, MECHANICAL ENGINEERING
>>
>>CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
>>
>>
>>
>>
>>
>>_______________________________________________
>>Diy_efi mailing list
>>Diy_efi at diy-efi.org
>>http://www.diy-efi.org/mailman/listinfo/diy_efi
>>
>>
>>
>>
>
>
>
>
--
STEWART PRINCE
PROFESSOR, MECHANICAL ENGINEERING
CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
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Yes, I see this now. If the reference for both cells are tied together internally,
the best way do to it would be to reference ground signal to 2.5 volts. This
makes an H-bridge unnecessary as any buffer with 0-5 volt DC output can drive
5mamp, easily. Thus, a PWM signal with a 50% duty cycle would equate to
Ipump=0 (on average) and with the proper selection of a series resistor,
a 100% duty cycle would equate to whatever positive pumping current is needed,
depending on what Air-fuel ratio you want to calibrate to, and a 0% duty
cycle will equate to a negative pumping current.<br>
<br>
One could size the op amp gain and the in-line resistor to yield the proper
max pump current at 100% duty cycle, but how does one know if the pump current
has really driven the nernst cell voltage back to .45 volts? I haven't modeled
this system, but I'm assuming that it is a type "0" system in terms of transient
response, meaning there will be steady state error. If you close the loop
(the purpose of the op amp) you will need a high gain to minimize the error,
and this might create "overshoot" and "ringing" of the circuit response.
Perhaps what you really need is to take the nernst cell signal, process
it using a PID algorithm, then send it out to the pump cell using PWM. This
sounds like a perfect fit for a microprocessor. I believe this is the path
we will take.<br>
<br>
Many thanks<br>
S. Prince<br>
<br>
Klaus Allmendinger wrote:<br>
<blockquote type="cite"
cite="mid3.0.1.32.20030227130537.0088e690 at innovate-tech.com">
<pre wrap="">Hi,
The pump cell and the nernst cell in uego sensors are physically bonded
together. The common junction between the two is what you refer as
'ground'. There is no way to separate them because they are connected
together internally in the sensor and only one wire comes out. The same is
true for other manufacturers wb sensors. A H-bridge design would require a
differential amplifier that outputs the difference between nernst+ voltage
and common ground. The difference then can be referenced to circuit ground.
In my experience a H-bridge is not neccessary because in normal operation
the required voltage to drive the appropriate current in/out of the pump
cell never exceeds about +- 2V. This means that a 0-5V digital signal can
drive the cell if the pump/nernst cell common is held at 2.5V.
Regards,
Klaus
Regards,
Klaus
At 02:12 PM 2/27/03 -0800, you wrote:
</pre>
<blockquote type="cite">
<pre wrap="">We're looking into closed loop fuel control on our FSAE car using the NTK
</pre>
</blockquote>
<pre wrap=""><!---->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. 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
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 have never
measured the internal resistance between the two cell references.
</pre>
<blockquote type="cite">
<pre wrap="">
STEWART PRINCE
PROFESSOR, MECHANICAL ENGINEERING
CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
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</pre>
</blockquote>
<pre wrap=""><!---->
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="$mailwrapcol">--
STEWART PRINCE
PROFESSOR, MECHANICAL ENGINEERING
CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
</pre>
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