Metal Detector using hall effect sensor

You can use a permanent magnet on one side of the tube with your detector on the other and try to detect diminutions in the magnetic field as ferrous material flows by, soaking up some of the PM's magnetic field.

If you need to detect were the metal are in the tube you can always use an IR pair to detect that there is an object, even any Ultrasonic distance detector will also help.

Would have to know a little more about how big is the tube what metal are you passing thru .  is it just going thru by gravity, etc.

If the metal uses most of the tube, i would drive 2 holes in the tube on oposite ends and use a ir led  emiter and receptor to detect when a object passes thru.  easier to implement.

Thanks Kevin,

Actually, metal detector should not detect a non-metal object. I am trying to make it as a new conceptual design and an ultimate application could be for example in a food processing industry where metal objects have to raise alarms only when they see an object with metallic contamination. In that case, an IR pair or ultrasonic detector might not do this kind of job.

Hey Don,

I guess it should be worth a try. Thanks for a nice suggestion.

Further extension to your question Kevin,

The width of tube will depend upon the detection range of the sensor. Sensors could sense the metals within earth's magnetic field, or an artificial field could be induced by using permanent magnets to magnetize the metal object (ferrous type only) thereby, making a job bit easier for the sensor to detect it.

Hi Umair,

I have moved my attention from your other posting to this one.

John

I am not sure that you can get a sensitive enough reading using the hall effect sensor.

Have you looked at the TI LDC board?  It is very sensitive to magnetic fields.

Also, some metals are diamagnetic, which means that they behave differently to magnetic fields than conductive metals.

DAB

John, the two threads mistakenly initiated. But we will continue here

Time is a fairly easy quantity to measure with electronics.  So, if we can translate our param of interest into something that modulates an oscillator, we may be on our way to a cheap and reliable system.  I suggest you google something like "What's all this V/F (or F/V) stuff anyhow" for more on this timelessly exciting technique.

Perhaps, you could wrap a coil of magnet wire around a plastic tube through which your stuff flows.  You could make an oscillator with this inductor as a timing element.  Ferrous stuff passing through the tube would make the coil seem larger electrically, slowing down the oscillator.

Ti has a circuit sorta like this that they use for turning springs into scales.  Maybe you could adapt it.

Hi Umair, What D_Hersey mentions reminds me of metal locators that I serviced years ago. They had two oscillators one of which was stable and the other had an external coil that was used as the inductor for the second oscillator. When no metal was present near the sensor coil the two oscillators were the same frequency and would cancel each other out on the audio discriminator of their beat frequency. If metal was moved into the area of the sensor inductor coil it would change frequency and the difference in the two oscillators would show up as a beat frequency and make an audio tone in the head set. I do not know if this system is still being used for metal locators but it seemed to work quite well on the simple models I worked on back in the 1970s and early 80s.

John