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This may be old news to some but others may not have read it.
HOW A PROTON MAGNETOMETER WORKS.
A SIMPLIFIED EXPLANATION By Mr Olson.
Detection distances of conventional metal detectors are limited by physics because they work by you having to constantly move and place a large loop or coil close to the ground. The metal detector then energizes the coil with current creating an artificial magnetic field and then letting this field collapse creating small delayed electric spikes in any metal objects that are close. The detector then turns into a tuned receiver and tries to pick up the small spikes for target detection. This happens many times a second.
The problem with this method is that the artificial collapsing magnetic field and then the detection of these spikes are only possible in close proximity to the coil. This small distance of detection is rarely more than twice the diameter of the coil being used. With a 10 inch coil you would have roughly a 20 inch maximum detection distance and so on. Also note that the farther from the coil, the smaller and smaller the detection spot gets because the zone of detection tapers out like a cone smaller and smaller from the coil.
P MAG being an absolute proton magnetometer has a huge edge over conventional detectors. Simply put it uses the earths natural magnetic field lines of flux which slice thru the planet like it’s not even there, to in a sense light-up or illuminate ferrous targets.
These lines of flux kind of vibrate at different frequencies at different areas of the world. This is what a gamma reading is. It’s a value that is actually a measurement of this frequency of vibration. Ferrous metals distort this fairly even natural field in the area close by the object. So with a proton mag we simply read the frequency of the field at the sensor and if there is an increase or decrease in the field we know that metal is nearby which caused this phenomenon.
Actually the proton magnetometer does not transmit anything. It simply creates a small artificial magnetic field the size of your fist right at the sensor coil for one second and then lets it collapse. The coil in the sensor then picks up the frequency of the protons as they scramble to realign themselves back to the natural field.
Believe it or not scientist still do not know exactly what this field is and how it works. It is a matter of great debate worldwide.
So in a nutshell all ferrous metal is naturally (lit up) so to speak by these lines of flux and we can find these metal objects with a proton mag by finding the distortions they create in the earths natural, fairly even gamma field. The larger the object is in mass and weight the farther away from the object this distortion occurs.
An example being that a car distorts the natural field for the size of a 200 foot diameter ball around it. So we can detect a car if we walk within a 100 foot radius of it. Getting a little closer at 75 feet from a car we get a very strong detection.
You cannot (see) or detect a car from 75 to 100 feet away with a conventional metal detector. Not even 10 feet with most.
This fall off in detection distance from the sensor is a factor of 8 for any magnetometer. So every time you double the distance from the sensor to the object you loose 8 times the gamma value of the disturbance that the object created and vice versa.
This also works the other way.
Let’s say you note a 3 gamma change in the natural field when your sensor is 30 feet from a 55 gallon steel drum. Now if you halved that distance by walking to 15 feet from the drum you would see that the reading at the sensor now would be 3 x 8 = 24 gamma change over the natural gamma field value. Remember that when walking around in a large field with no ferrous metal everywhere you went, the mag would read the same gamma value plus or minus 2 or 3 gammas.
Let’s say you are in central Florida and it is reading 47000 gammas. Now you see a 55 gal drum way off and you start walking toward it. The gamma value readout and the tone earphone growl would stay the same until you got to the far edge of the distortion that the drum is creating by its size and weight.
So now you are 30 feet from the drum and the tone earphone steps up three percent higher in tone and the gamma value readout has increased 3 gammas higher to 47003 gammas.
Now you walk closer to 15 feet from the drum halving the distance to the drum. The tone earphone would step way up in frequency and the gamma value would change by that factor of 8 again. You would now be reading 3 x 8 = 24 change or 47024 gammas on the read out which is a hugely unmistakable target. Remember that everywhere else in the magnetically clean field where there are no steel objects the mag only reads 47000 gammas.
If you now walk away from the drum to 35 feet from it, you are now back outside of the drums distortion area of influence and your gamma readout would be back to the natural value of 47000 gammas.
It is important to note that if you walked around to the other side of the drum, lets say to the south side and you approached it closer, you would again start detecting it at 30 feet away.
So the detection distance of the drum is a 60 foot diameter ball, which is basically round. 30 feet straight up into the sky and 30 feet down into the earth and of course 30 feet radius all around it.
The above information is very important and should be read over a few times until you understand the working concept.
This information is also the basis of determining the size and weight of an object that you have located but you cannot see.
NOW HERE IS THE BEST PART.
For example, to find a 55 gallon drum if someone buried it in a field not more than 25 or 30 feet deep you could search for it by "mowing the lawn". That means searching for it by walking straight lines spaced 40 feet apart. When you come to the end of a line you would move over 40 feet and then walk back down that line like mowing your lawn with a mower.
It would be impossible to miss this target because with 40 foot spacing between your search lines, your sensor could never be more than 20 feet from the drum at the most. Passing by the drum even at this farthest possible distance would still be an unmistakably large ( gamma value change) target.
The great point of searching with a magnetometer is that it is HANDS DOWN the best tool to use to find ferrous metal targets at the farthest possible distance. If you understand what you are doing it is not possible to miss a target when having used the proper (grid) for the search pattern for the size and weight of your target. Of course you should also throw in a fudge factor on the conservative side of your estimate of the possible weight of your target.------This can never be said about searching with sonar or conventional metal detectors. Sonar can be masked by thermalclines, fish and rough bottom. Metal detectors can miss a target because of the simple physics of their short range, the tapering cone of detection and the farther your target is from the coil. Also because of tall grass, bushes or under growth and because the ground soil creates masking effects to a conventional metal detector.
Ground soil reduces the detection distance due to the minerals in the dirt. The signal from a target is robbed in two ways because of this. First the minerals rob some of the strength of the out going pulse of a conventional metal detector. Then the minerals rob some of the signal strength of the slight ring produced by the metal target that is trying to get back to the coil that it a receiver trying to sense it. A conventional metal detector can never detect metal as far into the ground as it detects metal thru the air. (An air test)
You should use these explanations and examples to form your own search plan depending on the size and weight of the object you are looking for.
This example works the exact same way with a larger object like a car. An average car has a maximum distortion distance of 100 foot radius for 1 gamma change. So you will sense one gamma 100 feet away and if you half the distance to the car using the factor of 8 at 50 feet from the car you would have 1 x 8 = 8 gamma change from the natural field and so on.
Also unlike conventional metal detectors most ground or dirt has little to no masking effect on target detection distances with a proton mag. A regular metal detector may lose 25 to 50 percent detection distance if the object is buried in the ground verses how far you can detect it thru air only.
So if your car is hanging from a tree 100 feet over head or buried 100 feet below you in the ground you can detect it almost at an equal distance.
Now you are on your way to becoming an expert in the field of magnetometer search. Enjoy and find that lost treasure.