Hall Effect Sensor Circuit Design Question

Ive had a question for some time that I cant seem to find an answer for. I have a theory but thats it.

Example 96 Jeep 4.0l with a 3 wire hall effect crank sensor. Pull Down design circuit. PCM sends 5v down the signal wire and the crank sensor grounds the signal to produce a square wave pattern.

Question, what is the standalone 5v REF wire used for if the sensor only uses the 5v on the signal and grounds the signal to ground when required?

I can only think that the standalone 5v REF wire (Not signal wire) is used for some sort of signal integrity tests by the pcm.

Same question goes for pull up circuit designs except it would be the standalone ground wire that I would question.

Maybe one of you can fill in this gap I have in my knowledge.

Thanks!

The 5v ref is supplied from pcm and should maintain constant5v. the signal wire will return the 5v to the pcm till pulled down (vice versa for pull up sensor) so with no 5vref nothing happens on the signal wire

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Hmm I see i didn't actually answer your question lol hang on I'll see if I can find the reference material (if Tyler doesn't beat me to it)

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3-wire Hall effect sensors need a constant 5-12 volt power feed from PCM, a 5-12 volt reference from the PCM (pull down design), and a ground.

Ben, the signal wire will also have constant voltage coming from the PCM (pull down design) and the sensor pulls it down to ground. You can identify pull down or pull up by disconnecting the sensor and checking for the presence or absence of voltage on the signal wire (assuming PCM and wiring is good).

Thanks for the explanation willrogers!

I have seen a constant voltage on a signal wire (on a vw polo cam sensor) and thought it was shorted to + until i saw it pull down to zero lol.

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Thanks for the replies! Ya the jeep example has 5v supply from the pcm on the signal wire and 5v ref and sensor ground from the pcm as well.

Here is food for thought, cutting the signal wire on a 96 jeep 4.0 but leaving the 5v ref and sensor ground supplied to the sensor, then cranking the engine, you will not see any activity on the sensor on its signal wire from the sensor. Atleast not on the 20v scale i was on. Maybe on a 500mv scale i would. I think ill do some continuity tests with a spare crank sensor i have. After noticing i had no 5v square wave that is where my question came from. Thinking the 5v ref wire is only for integrity test. I dont believe it needs 5v power supply to be able to physically switch on and off.

So why would the sensor need a 5v power supply since hall effect sensors are simply a magnetic switch right?

What really confused me before is, i believe on some older chrysler or GMs the pcm supplies a sensor ground, 5v ref and 8v signal ref. Pull down design, Produces 8v square waves. So then, whats the 5v ref for.

So i found an article that goes into detail about hall effect sensors. They talk about the Hall effect sensing circuit and how it responds to magnetism which requires a power and ground source to function but since there is a magnet in our sensors it must move away and toward the sensing circuit. I had always thought it was just a simple switch internally.


www.electronics-tutorials.ws/electromagnetism/hall-effect.html

I guess i could have done research before but that article basically fills in the gap in my knowledge.

graywave,

this is a very good and complex analysis of hall effect sensors :



Have a look at part 5 as well.

Thanks bud.

The science behind the hall effect is what I needed, Thank you! Completely polishes off my knowledge on these types of sensors.