Hall effect sensors - Ferrous detectors/discriminators ?

[bugwhiskers]

The Hall effect sensors in modern hard drives have to be able to get data (bit streams) from the tiniest of tracks (magnetised domains) so they must be super sensitive.

One day...I keep saying that... I am going to get hold of a sensitive Hall effect sensor and site it in the middle of a PI type coil. I will treat it as the receive element and pass its output to the usual PI circuitry. I am hoping it will either respond or not respond very quickly to every metal it sees. If it saturates in the presence of ferrous metal I will be overjoyed as it could be used as a method of discrimination.

[chemelec]

Hall Effect Sensors Are Quite Sensitive, "WHEN Connected to an Appropriate Amplifier". You Can't Just put it into the Usual PI Circuitry.
Without an Extremely Good Amplifer, they are Not very Sensitive.

There are typically Two Types of these Devices:
1) Is a Hall Effect Switch. It Switches ouput at a Pre-Set Level.
2) A Linear Output Device: A Relative Voltage out Compared to the Magnetic Field that is present.

I stock both types and use them for Many Applications. But I Highly Doubt there Usefulness in what your Planning to do.

Take care......Gary
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The Hall effect sensors in modern hard drives have to be able to get data (bit streams) from the tiniest of tracks (magnetised domains) so they must be super sensitive.

One day...I keep saying that... I am going to get hold of a sensitive Hall effect sensor and site it in the middle of a PI type coil. I will treat it as the receive element and pass its output to the usual PI circuitry. I am hoping it will either respond or not respond very quickly to every metal it sees. If it saturates in the presence of ferrous metal I will be overjoyed as it could be used as a method of discrimination.

[99thpercentile]

Mag & EM on one platform

This is a very difficult problem. Some of my co-workers made system to do this last year, but it's probably out of your price range. Assuming that your EM system is either frequency domain (FDEM) or time domain (TDEM) there are two different ways to solve this problem. In FDEM you must null the transmitter (Tx) magnetic field at the magnetometer sensor, which is typically done by having a second coil inside the Tx coil which transmits a waveform that is out of phase with the primary waveform which nulls the field at the center of the coil. In a TDEM system, the magnetometer must measure in the off time of the waveform. The timing for this is very important. I have attached the reference and can email it to you if you are interested.

Butler, D.K., Bennett, H.H. and Ballard, J.H., 2006. Overview of multimethod geophysical system development for enhanced near-surface target detection, discrimination, and characterization. The Leading Edge, pp. 352-356

[wyndham]

In one of my stumblings around the net, I found a sensor that is a GMR (giant magnetic resistance) thin film sensor that can either be analog or digital versions and has been tested in detecting mines. This might be better than the hall effect either to eliminate the ground signal or to react to the tx pulse.
I don't have the url handy buta link from the mine detector apps page will go to the mfg and test kits are about $100 or less(I think).
Wyndham

[Wirechief]

Hello 99, how near the surface is he talking about?

Hi Wyndam, been awhile and I hope you are well and having fun with metal detecting. CU later and God Bless.

John Tomlinson,CET
John's Detectors

[wyndham]

Found the URL http://www.wsrcc.com/alison/uxopaper/index.html
the link is just down the page for the sensor.
Hey John just been maken pottery and trying to figure out how all you successful prospectors live so well on beans and fatback. I'd luv to live off of beeping but not today. CU later and Blessing to you and yours and BTW He has and does everyday.
Wyndham

[Wirechief]

Hi Wyndam, well one works 2 jobs to remain solvent haha! Thanks for the URL and I hope you are making some good finds lately. Ive been working the Minelab Musky last 3 weeks, quite a machine. I wish you the best Wyndam and yes he is continually blessing you and I . I hope to chat again and take care Wyndam.

John Tomlinson,CET
John's Detectors