controller Charge Pump?

[Luciano]

Hi,

See attached BMP file.

Nernst-cell internal resistance (Ri) measurement.

The circuit measures the resistance of the Nernst-cell and
also the resistance of the RiCall 82.5 ohm. Both measurements
are done with the same I/O, so we measure with the same voltage
when we source (+4.xx V) and when we sink (0.xx V).
The PWM is not used.

The AC current is ≤ 250 µA.
(See 250 µA current direction when the I/O sink or source).

The differential amplifier will output a voltage when
Ri and RiCall have different values.The output voltage is
measured with the A/D of the MCU. With the resistors you
can adjust the gain of the amplifier.

* * *

The Tech Edge does almost the same with the I/O but
they use a 910 ohm resistor so the current is more
than 250 µA. (???). The capacitor is the 100nF C201.
They use 2V as the virtual ground.

(See page 6 of the PDF for Max. current load of the Nernst-cell).
http://wbo2.com/lsu/Y258K01005e03mar21eng.pdf

* * *

This is just a theoretical circuit.
Never been tested.

Luciano

[toalan]

910 ohms would mean they are violating 250ua parameter by more than 10 fold with a 0-5v signal, c210 looks like it is just part of a lowpass filter to remove noise rather than to couple an ac signal into the nermest cell.

It looks to me that they really are powering off the sensor and doing a DC measurement of Ri. I also have no idea why they use an external DAC rather than the avaible PWM ports on the Atmega8 instead.

Luciano are you affiliated with Tech Edge? are you also building you own Wideband reader? Why are you using RiCal of 82.5? I believe it is a reference resistance for the nermest cell, shouldn't it be 80 ohms?

The way I am doing the Ri measurement is different as I try to use as little OP amps and resistors as possible and use a bit of digital signal processing instead.

[Luciano]

I see a problem with the circuit of my last post. (BMP file).

When we are not measuring the Ri of the Nernst-cell, the output voltage of the cell +2.95V (+2.5V +0.45V) goes through the two 10K resistors and the 82.5 ohm resistor back to the 2.5V of the virtual ground. (We have 20082.5 ohm connected in parallel with the cell).
The circuit will need analog switches (like the 4066) in order to insulate the Nernst-cell.

Two years ago I helped my cousin on a similar project.
He married, his wife sold the car, the project never started.

Luciano

[toalan]

oh yeah I was gonna point out the 2.95V thing but you beat me to it.

I recommend putting a 1uf or 100nf capacitor in series with the 10k resistors. The problem I see with the circuit without proper capacitors in place is that you require the Nermest cell to be perfectly .45V above your virtual ground. If the nermest cell is slightly below or above the .45V then your differential amp will output a difference. If you filter out the AC signal itself without the 0.45 required DC offset and use the diff amp on the ac signal itself then the circuit should be cool.

I made a mistake when I said that the TE unit powers off the sensor, It is jsut that I use coupling capacitors and when I did not see any I jumped to that conclusion.

[Luciano]

Interesting products:

http://www.bosch-motorsport.de/en/sensoren/sensor7.shtm

Page 1-2 Lambda Sensor Mini-LSU 4.9
Page 3 the AWS_LSU 4.9 (Sampling rate 100 Hz per channel).
http://www.bosch-motorsport.de/en/se.../MiniLSU49.pdf

Luciano

[toalan]

interesting, looks like the old LSU just in mini form.