The first observation. In the tests on the air, coin found at, say, 30 cm, and in the ground deeper than 18-20 cm it is impossible to find. All natural - sounding the signal is strongly attenuated in the ground.
The second observation is the significant deterioration in the quality of discrimination of the object in ground.
The device reacts to the earth as well as the coin behind it. Ie the detector at the same time it is necessary to distinguish the signals from the two objects. Therefore, the signal reflected from the ground, begins to "score" a weak signal of our coins. In this case, the quality of discrimination deteriorates, compared to air tests. And whether it is necessary to trust the tests of the detectors held on the air? And how better to conduct tests in real conditions?
Test 1. The depth dimension of objects detection.
Manufacturer of firm Fisher metal detectors to measure the depth of detection objects uses buried in the ground at an angle of 45 degrees plastic up. Inside the tube move special "rails" on which parallel the surface is a target.
With this simple device you can evaluate the sensitivity of the device to different targets at different depths.
Test 2. A simple test to determine the depth of detection of the patch.
In many cases it is possible to arrive easier. Take a test target, for example, the Soviet penny (it is most often featured in such rapid tests depth).
Put it in a small plastic bag with a clip. A sharp spade carefully remove the layer of the earth, sink to the bottom of the hole out a bag of coin and put it parallel to the ground surface. Measure with a ruler the depth and gently return the removed lump. The soil is very preceptive don't need. What we get?
The coin is in almost undisturbed and homogeneous ground; if we dug a pit, and then covered it with loose earth, the conductivity parameters the soil would have changed that would affect the depth of detection of the object.
Mild trampling down the earth helps to easily remove the coin back into the light of day and warrants that it will not go in great depth.
After all the dirty experiments the packet is discarded, the coin remains pristine and untouched.
Test 3. Depth of detection of the coin by the sound.
You can now arm themselves with several devices of different brands and conduct experiments. Perform tests in the following sequence.
Turn the device on. Wait 5 minutes to have installed its temperature.
Carefully balance at the maximum sensitivity of the device. If balance is not possible, reduce the sensitivity until, until is reached reasonable compensation of the earth.
For devices with built-in auto-tracking (i.e. the device is in operation, automatically monitors the balance of the earth and adjusts it himself) this option disabled. Why? The auto-tracking is not very stable on maximum sensitivity and slightly reduces the search depth.
Disable the discriminator and work in the mode "All metals".
Consistently, changing the depth, find this, which still could be the sound you detect it (but not identified on the display!). On this the depth of the discriminator can not correctly identify the genus of the metal.
It is desirable to conduct tests at different speeds of movement of the coil, according to various trajectory to simulate the search process, i.e. to start the test about a meter before target.
Test 4. Verification of thermal stability of the balance of the earth.
You want to delay the device for half an hour under direct sunlight, in order that he hot. To test thermal stability of the balance of the earth.
If "land gone", then it's almost a guarantee that measured previously the depth you will not find anything as the signals of the earth will score a weak signal of the target. You just miss the weak signals from deep-lying of the coin on the regular positives rasbalnsirovano of the device.
There are two ways out of this situation:
- to reduce the sensitivity;
- usually adjust the balancing of the earth.
Here we come to the most important conclusion: it is very important are no longer a super case of the detector, and the stability of its work!
You can make a device that the air would "sniff" the same nickle on two feet, but a little confused by this. Hardly it will be possible to balance this detector such sensitivity. But if he has and no matter the temperature stability, then you are in the search process will often have to adjust the balance of the earth, and it will be very distracting and tiring.
Test 5. Definition of maximum depth discrimination of objects.
It is similar to the previous one. But you will need to include the discriminator. In this case it will be necessary to look at the display (or to navigate by the sound) and to determine the depth at which it starts correctly be identified.
Depending on the device the depth discrimination of the object is reduced by 20% -50% of maximum (measured in the previous test).
Test 6. How to distinguish the signal from the coin and lying next to the beer tube.
Bury a coin, and next at a distance equal to the diameter of the coil - beer tube. So you can simulate the most common today metallometer.
Tube do not need to dig deep, because in reality they lie on virtually surface. Do such movements of the coil, by a sweep of the scan and tube, and a coin. Note the signal and display picture.
In the case, when the coil passes over the first coin, and then over the tube, the quality of identification will be higher.
Test 7. Determination of the depth of detection in static mode.
To switch the device into static mode (if it allows it design and conduct a second test. In static mode, the depth of detection most devices will be more.
Test 8. Assessment techniques search and scan frequency.
And the most recent experiment. For example, you found that with your device you can find Soviet nickle at a depth of 25 cm Select a plot of land. Ask buddy buried at this depth, the coin in an unknown place for you. Further you can try to find it. In this test you already own eyes can see, how important technique of search and scan rate.
Training and educational function tests
These tests can be repeated on different types of soil, e.g., clay earth, loose soil, sand. If the first time you hold in your hands a detector, such preliminary tests are very important. You will be able to evaluate real and not the claimed features of the device on real soil and real conditions.
In tests, try to notice small features:
- vibrations;
- the picture of the spectrum.
Evaluate the influence of the nature of the movements of the coil, the effect of differential ground level and metallometer on the quality of object identification. For starters, you can mention the following:
- if the target uses a coin, then with increasing depth range "smeared" sound becomes less clear.
- with increasing depth of occurrence shifts the position of the object on the scale discrimination (or the number of VDI).
Stronger is the dependence of the correct identification of the velocity of motion coil and its trajectory. Discrimination is deteriorating very fast, very slow or uneven speed.
Try moving the coil is not parallel to the ground, and on a shallow trajectory, because when in the extreme positions the coil does not remain strictly parallel to the ground and rises slightly. So are usually the inexperienced searchers. The quality discrimination will worsen.
Moving coil with a small amplitude just above the center of the target, you will be to watch the best quality of identification. Use this technique to clarify object identification.
There is such situation, when the coin has a small depression in the ground or either side there is a differential level of the soil. In this case, too worsens the discrimination of the object. Can reduce the amplitude of the oscillation coil, so in the end positions is not to go on the hills. You can try to scan from a different angle.
It is very important to hold the coil as close to earth as it would "caress" her. Not it is worth to sacrifice the depth of the search at the expense of speed.
It often happens that when moving in one direction, the instrument shows that in the ground is the object of non-ferrous metal, the reverse movement is silent. In this the case will determine the exact location of the object and change the trajectory of coil so that it moved exactly over the center of the object. Can remove the top a layer of soil, the signal level will increase, and identification will be more accurate. Or sweep the coil perpendicular to the original direction. In any case, to ignore such signals is not necessary.
Author: S. L. Dubrovsky