Using an electromagnet as a magnetometer

[Sam Brown]

I am new to this site and I am not a physics / engineering professional. Please excuse me if I only have a layman's understanding.

I have been trying to make a device to sense a 2 foot long by 2 inch diameter rod at an 8 foot distance (all steel, all ferrious). to be detected. I have tried home made magnetometers with rare-earth fixed magnets, etc. Bascialy souped up compasses.

The Neodymium magnets will only work to about 3 feet max.

My idea now is to "boost" with power: make a home-made electromagnet (DC current, very simple) over some 2" steel bar stock and powered by a 6VDC lantern battery (with suitable current limiting resistor). The electromagnet would be suspended by several thin sewing threads. When switched on, it would be pulled just a hair towards the mental bar 8 feet away. I can detect that small movement and thus have my yes/no answer to the question "is it there 8 feet away or less?"

My question is does anyone know if this would work as I want / hope or am I just barking up a wrong tree?

Thanks in advance.

Sam

 

[berkeman]

I am new to this site and I am not a physics / engineering professional. Please excuse me if I only have a layman's understanding.

I have been trying to make a device to sense a 2 foot long by 2 inch diameter rod at an 8 foot distance (all steel, all ferrious). to be detected. I have tried home made magnetometers with rare-earth fixed magnets, etc. Bascialy souped up compasses.

The Neodymium magnets will only work to about 3 feet max.

My idea now is to "boost" with power: make a home-made electromagnet (DC current, very simple) over some 2" steel bar stock and powered by a 6VDC lantern battery (with suitable current limiting resistor). The electromagnet would be suspended by several thin sewing threads. When switched on, it would be pulled just a hair towards the mental bar 8 feet away. I can detect that small movement and thus have my yes/no answer to the question "is it there 8 feet away or less?"

My question is does anyone know if this would work as I want / hope or am I just barking up a wrong tree?

Thanks in advance.

Sam

Welcome to the PF, Sam.

Can you say more about the application? Is the pipe in the ground, or sitting out away from the ground? If it is not buried in the ground, it is probably easier to detect it with an RF "Dip Meter". Is the length always the same?

 

[jim hardy]

I spent a while last night looking for DIY "Fluxgate Magnetometer " , found some interesting ones in astronomy forums of all places.

Two of them mounted a few feet apart can make a sensitive metal detector. The premise is ferrous metal distorts the Earth's magnetic field near it. When your magnetometer pair is brought near, the one closest senses that distortion first. So taking their difference gives you indication you're approaching something that's probably ferrous. It's called "Differential Fluxgate Magnetometer".

If you're an electronic hobbyist, try searching . Surely somebody makes a kit..

Here's an old PF thread on metal detectors
https://www.physicsforums.com/threads/simple-metal-detector-circuit.922301/

I have tried home made magnetometers with rare-earth fixed magnets, etc. Bascialy souped up compasses.

Can you post a picture of your apparatus ?

good luck.

 

[tech99]

Jam jar magnetometers are used for detecting variations in the Earth's field and solar storms etc. I came across this one on the web:
http://www.eaas.co.uk/cms/index.php?option=com_content&view=article&id=74:how-to-make-a-very-sensitive-jam-jar-magnetometer-by-robert-cobain&catid=10:equipment-reviews&Itemid=16

 

[Sam Brown]

Thank you everyone!

Thank you for getting back to me with ideas so fast!

The bar is always the same. It is in the air and not in the ground (or not there: that is what I hope to be able to detect).

I have tried a fluxgate magnetometer and that seems to work but only to a range of about 2 feet or so: I need greater range. I only need to know the YES / NO presence of the bar. I do not need to know direction / speed of motion / orientation, etc.

Its akin to a motion detector in principal: just for the presence (or lack of) this bar.

There is not apparatus as yet, I am trying to figure out the best way to build it! :-)

Berkeman: You may be on to something I did not think of: are you talking about the old GDM (Grid Dip Meters) Hams used back in the day? If so that might work(??) I wonder if someone had one lying around and might try it (I would assume a very very low frequency) do see if it puts out a nice big field and has any distortion in the field at 6 - 8 foot distance by the bar?

 

[Sam Brown]

Tech99:

I made something similar but works only to 2 -3 feet. I will look at this article in-depth. Perhaps I missed something. Thank you!Thank you all again!

 

[Sam Brown]

But would the method I outlined work? I am not concerned with an electromagnet affecting the bar in any way. I just want the electromagnet to move a smidgen in the presence of the bat at (at least) 6 feet (aprox 2 meters) which i can detect.

If this idea will work, could anyone tell me roughly its specs. (I am not an engineer). So if you think it would work: "Take xxx length of yyy diameter bar stock, wrap with uuu turns of rrr gauge wire, hook to vvvVDC and whala! You have your sensor of sorts".

I thank you all again!