Calculating Distance for Hall Effect Sensor Activation

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Discussion Overview

The discussion revolves around calculating the distance required for Hall Effect sensors to activate in the presence of neodymium magnets. Participants explore the relationship between the magnetic field strength of the magnets and the sensitivity of the sensors, with a focus on estimating the necessary proximity for activation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about estimating the distance a neodymium magnet must be from a Hall Effect sensor to activate it, given the sensor's sensitivity to a 5 Gauss magnetic field.
  • Another participant suggests that the Hall sensor should perform well at several centimeters from the magnet, indicating a potential issue with the sensor if activation requires closer proximity.
  • A clarification is made that the Hall Effect sensor does pick up the magnetic field at a few centimeters, but the participant is looking for distance estimates for different sensor sensitivities.
  • One participant mentions that the field of a long bar magnet can be approximated by a formula similar to Coulomb's law, suggesting further research on this topic.
  • A question arises about the distinction between H-field and B-field in magnetic contexts, with a participant noting that Hall sensors respond to the B-field.
  • Another participant emphasizes that both H and B fields are relevant in magnetic problems but that Hall sensors output based on the B field, leading to potential confusion in terminology.
  • A participant reflects on the influence of magnet length on the sensor's activation, proposing that shorter magnets might affect the sensor differently than longer ones.
  • One participant acknowledges finding a resource that partially derives the B-field equation based on Coulomb's Law, intending to share it for future reference.

Areas of Agreement / Disagreement

Participants express varying opinions on the relationship between magnet distance and sensor activation, with some suggesting that the sensor should work at a distance while others note the need for closer proximity. The discussion includes differing views on the relevance of H-field versus B-field terminology, indicating a lack of consensus on these points.

Contextual Notes

Participants reference the need for specific formulas and approximations related to magnetic fields, but there are unresolved details regarding the exact calculations and assumptions involved in estimating distances for sensor activation.

BradyChan7
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I have what I thought should be a relatively simple problem, but a quick trip around the Google makes me wonder. It might be easier to just ask some real humans for once...

I'm working with Hall Effect sensors and neodymium (NIB) magnets. I basically know the strength of my magnets, and the sensitivity range of my Hall Effect Sensors, but I wanted to know if there was a way to calculate how close the magnet had to be to the Hall Effect Sensor to make it come on.

In other words, I know that my magnets are rated at about 2,000 Gauss (I thought Gauss was a unit depending on distance, though, so if I'm right about that, I don't know what distance these are measured at), and I know that my Hall Effect Sensors should activate in the presence of a 5 Gauss B-field. I've noticed that I have to get my magnets really close to the sensors to get them to come on.

I was wondering how I could calculate (no need for a lot of precision, just a good estimate within a cm or two) how close I need to bring the magnet to the Hall Effect sensor to get it to come on.

I've seen a similar question involving a bar magnet, but I'm not sure if it applied. For clarification, the Hall Effect sensors we have are polarized, so I'm bringing the magnet closer to the sensor with the proper side facing it.

Thank you to anyone who takes the time to read this. Even the smallest advice will be appreciated.
 
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Neodymium magnets are quite strong (if properly magnetized). The field intensity decreases with distance from the magnet, but 5 Gauss is a small field. Therefore, your Hall sensor should perform well at several centimeters from the magnet. This makes me think there's something wrong with the sensor.
 
Sorry for being unclear earlier.

The Hall Effect sensor is picking it up at a few cm away, but we're going to try choosing new Hall Effect Sensors (for a different reason), and as I look up their sensitivities, I need to know how close our magnets will need to be for those different sensitivities.

Thanks so much for the reply!
 
The field of a long bar magnet is approximately given by a formula that resembles Coulomb's law (although there are no magnetic charges). Try googling it (I can't remember the exact form)
 
Don't mean to de-rail your thread, but when dealing with magnets aren't you dealing with an H-field and not a B-field?

I always though B referred to magnetic induction.
 
Both H and B are present in every magnetic problem. However, Hall sensors give an output proportional to B.
As for the names, I've always considered they're confusing. Thus I always refer to B or H explicitly. The word induction has been overused. First in electrostatics, later with Faraday's law and, in this context, with B.
No wonder students get confused.
 
According to the manufacturers' data sheets on all of the Hall Effect Sensors I'm looking at, it's the B field. I myself never remember which one is which, just the equations relating the two. My EMag Engineering Prof had a good way of telling them apart, but I've forgotten it now.

I'll check out the concept you mentioned Gordianus. Is the length of my magnet going to factor in? I know looking at the magnetic field lines, it seems that if it's a shorter magnet, both sides of the magnet are more likely to effect my sensor if the magnet is shorter, as opposed to longer.
 
I mentioned a long bar magnet only because the field B can be computed with the aid of an approximate formula. However, both long and short magnets can be used with Hall sensors. The closest "pole" always dominates.
 
I think I have it covered now.

I found this link, which has the B-field equation partially derived, based on Coulomb's Law, like you mentioned, Gordianus.

I'm posting it here so if anyone searches the same question, they'll get this information as well, and not have to post about it.

http://instruct.tri-c.edu/fgram/web/mdipole.htm

Thanks to everyone who replied!
 
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