Hi everyone,

I am looking for some help on understanding what might be a really simple question, however I am having trouble finding the information to answer my question.

I understand the basic functionality of the hall element. A magnetic field comes to the hall element and creates a small voltage which is amplified to provide a signal.

My question is this. I work in the automotive industry and we use hall effect sensors with ferrous reluctor wheels. Could someone explain in detail how this causes the hall element to detect and create the on/off circuit?

I understand the ferrous material will alter the magnetic lines of flux of the hall effect sensors internal magnet but I need some more explanation.

Thank you in advance for the answers and your time.

 

I understand the basic functionality of the hall element. A magnetic field comes to the hall element and creates a small voltage which is amplified to provide a signal.

Is how I understand a hall sensor works. Chrysler products used to have a "windowed" rotating assembly in the distributor with a magnet on one side, and the hall sensor on the other side. It would detect the openings in the rotating part to signal ignition timing. Basically the magnet is separate from the sensor and moving the magnet closer, further, or shielding the magnet from the sensor is how they work.

I understand the ferrous material will alter the magnetic lines of flux of the hall effect sensors internal magnet but I need some more explanation.

This sounds more like a variable reluctance type sensor. Hall effect do not have internal magnets from what I know. VR sensors are usually a toothed wheel that moves past the sensor and create A/C voltages. With the right parts you can actually create a rather large voltage that will probably need to be clamped in some form to protect what it's connected to.

 

Really, the actual "Hall Effect" in a semiconductor Hall device is to produce a small current across the device in response to a magnetic field. The hall effect ignition system pickups are used because they were more rugged and less expensive than the sensors that used a coil, and also because the output does not depend on the rate of the change of the magnetic field. That makes a difference during cold cranking with a weak battery.

 

When working in the aviation industry I used to install proximity switches. They would detect when something like the wheel well door being closed and latched. I believe those had a magnetic element in it. When the ferrous door latch would engage the proximity switch would detect it and give an indication in the cockpit that the gear was up and locked. Actually there was a prox on the up and lock arm. Down and lock as well. Without a signal from those locks and latches the pilot knew he could not depend on the actual gear positions. But if I recall from back in the 70's they had their own magnetic source. And I don't know exactly how they worked. So admittedly, I could be wrong but I don't recall ever hearing about Hall effect transistors that far back in history.

[edit] Just looked at a couple videos on prox switches. There are apparently many different types. So what I said foregoing is not completely accurate. So to answer your question:

Could someone explain in detail how this causes the hall element to detect and create the on/off circuit?

A change in the magnetic field causes a change in the output of the sensor. That change is detected via other electronic circuitry. Then whatever that circuit is designed to do - it does it.
[end edit]

 

In the 1970s most likely it was a permanent magnet and a reed switch doing the sensing.


Hall effect has been known for decades, but the sensors had too much noise and thermal drift. But with the integration of the sensing plates and offset canceling circuitry, the modern hall sensor was born.

 

NONE of the proximity switches that I have used in industrial applications used magnets, because they had to sense non-magnetic metals, mostly aluminum.

 

I have used both kinds of proximity, one that requires a magnet and the kind that just needs ferrous metal.

 

I've done many a equipment modification to replace the old variable reluctance sensors with new Hall based sensors to reduce the speeds needed to detect motion.
https://forum.allaboutcircuits.com/threads/pcb-manufacturing-recommendation.155412/post-1344613


https://forum.allaboutcircuits.com/...ing-device-magnetic-sensor.121871/post-976600

Many times I also needed to simulate the original signal to the controller.

 

Pro's & Cons

I have mostly used the more recent Hall effect.

 

thank you everyone for your responses. I appreciate the assistance on this subject. Turns out my assumption and understanding was wrong, while I did know how the hall effect worked I had at one point made an assumption that it can also work by using a ferrous reluctor. After doing some thinking and with this thread I have realized that I never should have made that assumption.

Thanks again!

 

It is actually very refreshing to listen (or shall I say, read) to a thankful reply from a fellow member who has improved his understanding of electronics just a little more.