Hall effect detector

[daverave]

thanks for the diagrams it makes things easier for me to understand....the above diagram is this how i would place sensors inside coil also would i need magnet in centre of coil ???? shame your sensors didnt survive reverse power supply...im still waiting for mine to be delivered from australia...i ordered only 2 of these and a different type from china ebay which was a lot cheaper...i was looking at a detector on the internet last night called a black hawk wh ich is pulse with iron discrimination....looks very impressive with large colour screen and claims better proformance than minelab gpx 5000 at about half the cost....but i will never be able to buy one unless i win the lottery !!!!!!!!!!

[Qiaozhi]

thanks for the diagrams it makes things easier for me to understand....the above diagram is this how i would place sensors inside coil also would i need magnet in centre of coil ???? shame your sensors didnt survive reverse power supply...im still waiting for mine to be delivered from australia...i ordered only 2 of these and a different type from china ebay which was a lot cheaper...i was looking at a detector on the internet last night called a black hawk wh ich is pulse with iron discrimination....looks very impressive with large colour screen and claims better proformance than minelab gpx 5000 at about half the cost....but i will never be able to buy one unless i win the lottery !!!!!!!!!!

The Black Hawk is a product of OKM. On their website there's a video that purports to demonstrate how to ground balance the unit, but what I found myself listening to was somewhat confusing. During the demonstration the sample is set to around 50 (which I presume equates to 50us). A calibration button is then pressed, and the person doing the demonstrations says "I'm going to swing it [the coil] so that it will be able to recognize ferrous and non-ferrous objects". After that he goes on to detect in a nearby area and gets a signal from a target, that incidentally is not recovered.
I'm not sure what their understanding of ground balance is, but it doesn't seem to match the generally accepted definition.

The product details include the following statement:
"Another advantage is that this pulse induction metal detector can be used in nearly all terrains and does not respond to typical iron mineralization or black sand."
Which would of course be the case if the sample time is set to a long delay of 50us.

There is also mention of an SCMI sensor, which I take to mean a Stray Current Mapper Interface. So it looks like this is an amalgamation of a PI and a magnetometer.

[daverave]

when you say stray mapper interface you mean like a magnometer sensor like fm3 ???? im not sure what to make of OKM...ive seen some bad press on you tube about some of their products not working...i was impressed with the look of the black hawk but i think the display is a bit over the top for the basic settings.

[Qiaozhi]

when you say stray mapper interface you mean like a magnometer sensor like fm3 ???? im not sure what to make of OKM...ive seen some bad press on you tube about some of their products not working...i was impressed with the look of the black hawk but i think the display is a bit over the top for the basic settings.

They mention an SCMI sensor on their website, and I can only assume that this is a magnetometer. Whether it's actually an FM3 sensor, or not, I've no idea. I can only read between the lines of the marketing gumpf.

[TH Jim]

Quickly, off the top of my head i seem to remember Carl mentioning a while ago that whites (i think) had put a magnetometer in a PI unit some time ago. I wonder what type of Mag it was????

I have a bunch of these A130x hall effect sensors - they good fun!!!

[daverave]

can you get good depth discrimination on iron with your A130x ??????

[Waikiki_Sweep]

I have found that magnetic conductors, attached to Hall sensor increasing its range significantly. I will work on this direction.
Who can tell what material is better for such "antennas"? Ferrite, Metglass, transformer cores?

[daverave]

maybe a ferrite rod would be better for this purpose being made of powered iron....as it should concentrate the magnetic field...when do we sample the outputs of the 2 hall effect sensors ???? will the samples be in the same position as for non ferrous on the decay curve then maybe drive a lcd or bar graph display to show the presence of iron...what you think ????

[Waikiki_Sweep]

maybe a ferrite rod would be better for this purpose being made of powered iron....as it should concentrate the magnetic field...when do we sample the outputs of the 2 hall effect sensors ???? will the samples be in the same position as for non ferrous on the decay curve then maybe drive a lcd or bar graph display to show the presence of iron...what you think ????

That one millivolt have to be amplified to go to indication.

Also I have found that presence of strong magnets even in opposite direction is bad for sensor. It goes blind. So I tried to move magnets to the ends of antennas and it works stable.

[Waikiki_Sweep]

Magnet + Magnetic Field Field Conductor + Hall Sensor - Looks good for pinpointer

If magnetic field conductor provides reasonable power of field to Hall sensor (non making it blind) so this configuration works pretty decent for ferric targets pinpointer.

[Waikiki_Sweep]

WHY NOT?

[daverave]

i know garrett make an FX ferrous probe like a long rod...but i always remember a product i saw some years ago on the internet called a ferrous hound which clipped onto the search coil of a pi detector and claimed full depth discrimination on iron...the size of this ferrous hound made me think that they had used hall effect sensors.

[Qiaozhi]

i know garrett make an FX ferrous probe like a long rod...but i always remember a product i saw some years ago on the internet called a ferrous hound which clipped onto the search coil of a pi detector and claimed full depth discrimination on iron...the size of this ferrous hound made me think that they had used hall effect sensors.

I don't think the Ferrous Hound is still in production. Even the trademark of "Ferrous Hound" has expired.

The MagnaWand is supposed to be a more sensitive instrument -> http://magnawand.com/Home.html

[Waikiki_Sweep]

i know garrett make an FX ferrous probe like a long rod...but i always remember a product i saw some years ago on the internet called a ferrous hound which clipped onto the search coil of a pi detector and claimed full depth discrimination on iron...the size of this ferrous hound made me think that they had used hall effect sensors.

I have some doubts that Hall sensor will be sensitive enough to go full depth but we may continue to try is.
Also probably that device you have mentioned is using magnetometer because magnetometers are much more sensitive.
Here you can see how to assemble magnetometer with 555 timer and Metglas from "Electronic article surveillance" tag.






Also I have checked that if you disconnect FET and bypass sampler your SurPI will start to work like Coil Magnetometer detecting ferric targets “drill bit” size or bigger.

[TH Jim]

Hi Folks,

@ Daverave, No, a hall effect sensor will not detect metal, it only detects magnetic fields. As Waikiki_Sweep has posted above, we can use a permanemt magnet to create a field near the sensor that is distorted by a nearby iron target moving through it, and detect the presence of the iron this way. Forrest Mims III has some good circuits for these sensors in his 'mini engineers notebooks' series.

I have also found the Metglass mag to be more sensitive at detecting iron than the A130x + magnet combination. All good fun tho! :-)

VERY interesting Surf PI mod, I shall be trying that one myself! Thanks for sharing that info Waikiki_Sweep

Regards, Jim.