DIYEFI.org Forum

The accuracy of your multimeter, or accuracy of resistors chosen?

How do you know that the heater is 100% for sure? :| I'm just thinking of points of failure, from that it might make better sense. The nernst cell, I wouldn't think would be the likely failure point, the heater and ceramics would be though... I did take a squiz at the schematic earlier, it's certain...

A quick test of the heating element would be to measure it's resistance. Not having used widebands before, I can't be 100%, but I'm guessing that the heater is the failure point of these sensors.. Check the resistance of the heater element - expect a few ohms, not a perfect 0, and not open circuit, ...

What angle is your sensor installed at?
I wonder if it's finally condensate affected?

I assume you've checked all wiring, as an intermittent wiring issue can cause issues.
As can PCB traces which oxidize over time...

Subver,
Thanks for the schem.
That format of schematic is difficult for me to read though

Missing from it is the base to ground resistors on the FETs? Without them, won't they float and when floating they can switch rapidly and cause the FET to overheat / melt??

Perhaps it was going rich / lean so fast that persistence of vision came into effect with the LEDs?

I like the Op-Amp idea, I'm sure it'll need testing, but the concept you put forward sounds good to me. The MCUs work is then limited to simply providing the heater, reading the current and reading the vgnd voltage (for greatest accuracy, don't assume 2.5V). I'm yet to buy O2 sensor, was going to do...

Isn't the IP current an AC current?
Or is it AC just by virtue of the sensor going lean / rich?

If the Op Amp was oscillating, I'd suggest the load was not enough? A bigger cap / lower value resistors?

Bump (any thoughts)?