A/C speed sensor - DC reference voltage from controller

I have a general theory question I guess, sorry if this is a basic one

Is this common/has anyone seen on speed sensor circuits (transmission/engine) of the A/C 2 wire inductive type - controllers outputting a small 0.2-0.5v DC reference voltage? Just so the controller knows the circuit integrity is in tact

I find that bias voltages on variable reluctance sensors are common, but not necessarily in the .2-.5V range. Usually more like 2.5V or 5V. Nissan for many years used a .3V bias, but on their O2 signal circuits. :silly:

Is there a specific vehicle you're testing?

Ah thanks - 'bias' voltage term helped me find my answer in one of danners O2 sensor/bias voltage vids. No specific vehicle - just trying to wrap my brain around whats happening from a theory stand point/general understanding of controller to speed sensor relationship I guess.

I just found it weird how the controller will output a DC bias voltage to an active AC voltage sending sensor, na mean? - But maybe the AC voltage doesnt matter so much as the frequency its sending?

So hypothetically would that be an AC + DC mixed voltage circuit?

Oh yeah, it's weird! :silly: Definitely throws you for a loop the first time you see it.

From what I've gathered, the module that the variable reluctance sensor reports to is mostly concerned about when the signal crosses a voltage threshold. It 'sees' 2.5V (for an example) as zero, and only sees a pulse when the signal goes higher or lower by a predetermined amount. How much higher or lower past that threshold isn't important to the module, just that the signal crossed it.

Chapter 21 in Paul's book has an awesome capture of this taking place, if you haven't seen it already:

that explains my question perfect, thank you! I might have to buy this book now