Offset Voltage Question

Groiunded and regrounded. Currently have a 12 guage from WB analog ground wire back to battery negative post. Have taken two 14 guage grounds back from MPVI interface EIO (ports 5 and 6) to same battery negative post.

This is my best voltage readings so far with the additional grounding at Free Air CAL- on my AFX:

WB analog signal = 4.96 V (confirmed by two meters)
HPT Voltage Histogram = 4.8127 V

Does this alone warrant an offset adjustment?

If so, do I offset 4.96 back to 5 V?

Or do I offset 4.8127 V back to 4.96 V?

Or do I offset 4.8127 V back to 5 V?

What wideband are you using?

I was using the PLX-300 previously. I was simulating the NB then. It normally read lean resulting in a slightly richer tune. However, good enough not being good enough I purchased an AFX, removed PLX, added a bung, put both NB's back, and have been spending more time grounding, super-grounding, calibrating, offsetting, and am slowly tune by tune with the AFX getting back to the last one I did with the PLX. Hey practice makes perfect and warming up to FI this spring.

You want a better idea of whether the observed error
is offset error, gain error, a limiting / linearity error in
order to correct appropriately.

I recommend that you take at least three measurement
sets - say, 0.000V out, 2.500 and 5.000 settings at the
wideband, verified with a DMM at the wideband output
to wideband ground (open circuit) and again with the
whole wireball hooked up as-used.

If 0.000 and 2.500 are dead-nuts and 5.000 is whack,
it means you have a linearity problem and not an
offset problem - and "fixing" offset for 5.000V will
then jack your 0.000, 2.500V data.

If it is a true, ground-loop offset then a significant
part of that may be from WBO2 heater current,
and heater current is ambient temp and load-point,
time-at-load-point variable so today's sweet tweak
is tomorrow's sour note. An instrumentation amplifier
which takes its input signal and reference from
inside the wideband (out of the current path,
close-in to the output signal driver & its ref gnd)
and its output reference from the EIO, could get
rid of common mode offset. I've played a bit with
this, you'd need an instrumentation amp IC and
a pair of 9V batteries, or a single battery plus
some regulators etc.; need to float the local
supply to keep from adding yet another ground
to the stew, etc.

"Somebody" should have a look at the EIO cable
alone, for applied vs reported channel voltage
and input current vs input voltage.

First 3 paragraphs I experimented with over the past few weeks. I had read your post about elsewhere on the non-linear treatment of the offset. I also read a thread (12Sec or 5Liter?) about being sure to have vehicle running for free air calibration and voltage checks (bung plugged). That increased the idle voltage from 4.96 to 4.97 at WB to EIO. Read elsewhere about AA battery test thru EIO to HPT with jumper in EIO signal to record raw voltage. This verification was dead on with multi-meter. At 4.97 this is fairly accurate output from the WB, my greatest error is with HPT recorded voltage which I believe the AA battery test and the improvement with heavier grounding prove out.

Your lead-in on your 4th paragraph raises a new question I have not considered to this point and that is WB heater (power to ground, duh me). Good point to think about, thanks.

As for the rest of paragraph four, that looks like a new hobby that might require some considerable commitment. Tabled for now but not forgotten.

Your last paragraph.....the spot on AA battery test eliminated that one I think unless there is something non-linear happening in the EIO Interface on and it just happened 1.48 V was spot on. I have really been focused on grounding as the issue and your WB heater comment is a very good place to look next. Wow a forest. Thanks again.