Hi Paul.
I've watched this chapter a few times and I was wondering if you could clear something up for me. You've always referred to a floating ground as being some type of bias voltage on the sensor ground to bring it up off the noisy block ground. You talked about some vrs sensors with signals on the sensor positive and sensor ground having a floating ground which I assumed came from the bias voltage on the vrs sensor positive combined with the internal resistor on the signal ground causing the ground voltage to rise. So I was thinking the floating ground was supplied by the 5v bias on the positive through the positive resistor and the sensor. But then you talked about a vrs with floating ground but no 5v bias. So where is the floating ground coming from? I went back through the book and realised you were referring to the vrs signal itself on the ground as the floating ground. Not the bias. But then a student asked if this floating ground was the same as what's used on chrysler O2 sensor grounds and you said yes and explained that the floating ground brings it up off block noise. But the bias there supplies the float. Not the sensor signal itself. Do you just use the term floating for both a ground signal and a ground bias or is there a difference. If so where does the float come from on vrs with no bias?
AdrianFQ wrote: Hi Paul.
I've watched this chapter a few times and I was wondering if you could clear something up for me. You've always referred to a floating ground as being some type of bias voltage on the sensor ground to bring it up off the noisy block ground. You talked about some vrs sensors with signals on the sensor positive and sensor ground having a floating ground which I assumed came from the bias voltage on the vrs sensor positive combined with the internal resistor on the signal ground causing the ground voltage to rise. So I was thinking the floating ground was supplied by the 5v bias on the positive through the positive resistor and the sensor. But then you talked about a vrs with floating ground but no 5v bias. So where is the floating ground coming from? I went back through the book and realised you were referring to the vrs signal itself on the ground as the floating ground. Not the bias. But then a student asked if this floating ground was the same as what's used on chrysler O2 sensor grounds and you said yes and explained that the floating ground brings it up off block noise. But the bias there supplies the float. Not the sensor signal itself. Do you just use the term floating for both a ground signal and a ground bias or is there a difference. If so where does the float come from on vrs with no bias?
You have no idea how much I have research this topic. The issue I find when researching AD converters (analog to digital) is non of the material is automotive specific in application. To be honest, this is a question to ask an electronic engineer.
My short answer is yes, I've used the same term for the bias voltage run on ground circuit and the VRS with a signal on the ground wire. It is probably not accurate to do so but I don't know what else to call it.
As long as you understand how it affects circuit diagnosis and testing, that is the most important part. Maybe one day I'll be able to answer this better.
@Dylan, I'm not smart enough either
The input resistance of good DVOM is about 10,000,000 ohms, proper scopes are a more or less standard 1,000,000 ohms. with so much resistance blocking the flow of current any phantom voltage that has builds up on a computer input pin is going to show on the meter..
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I have a question about a Vrs crank sensor on my Hyundai Accent 2001.
I saw your lectures again and i finally though i undestood what you ment when saying floating ground.
Long story short,sensor plugged in KOEO i measure on one wire 2.5 volts,and i think that's the signal,i measure the second wire and get 2.5 volts again,i unplug the sensor there is 2.5 volts on each wire again,so what kind of bias voltage is that?
Can we say that both wires are signal wires?
Doing a crank measurement connected only to one wire and to battery negative ,peak to peak i get 2.5 volts on the scope.If i connect to both wires i get peak to peak 5 volts on the waveform.
They are both signal wires, the way I would look at the signal is to use two channels and use a Maths add function on the scope to add the signals together.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
On a vehicle "ground" is ultimately a reference point. A specific reference point that is used to measure all other points. There was a time when some vehicles had a positive ground.
A "floating" ground can be thought of as a "non ground point" reference point.
It might be fed by a super simple voltage divider or it might, and likely is, part of a differential amplifier circuit. The bias voltage found on some systems is not easy to explain. I think we get ourselves into trouble when trying to do so without the actual circuit schematics.
For example... many vehicles have a bias voltage on the O2 circuit. When the sensor warms up and becomes active, the circuit is no longer open. You have multiple voltage sources. Yet... these voltages do not algebraicly add up. The source of the bias voltage goes away.
A bias voltage can allow for a logic system to be stabilized when an input is missing.
There are a lot of moving parts to this discussion. IMHO, it would be better to be very specific
