Question: (Billy):With most of the newer detectors how much sensitivity (depth) is
lost by using descrimination mode instead of all metal and can a
detector using descrimination mode make a mistake, for instance
a silver dime or quarter at 9" be read as a pull tab?
Answer: It is very well known that All metal mode goes deeper than Discrimination mode in good and no-trashy soil conditions. The signal does not pass through discrimination process therefore the target is very well identified. When discrimination is enabled then signal passes through it and might be filtered out as an unwanted target, if the target is deeper this loss is more clear since machine thinks of it as an small trashy object and rejects it. In Bad soil conditions and very trashy areas surprisingly Discrimination Mode goes deeper simply because mineralization and trash does not let the real signal to be distinguished in all metal mode. Generally, All metal seeks deeper in good soil conditions and specially works better for smaller objects like nuggets. Target ID in ALL MAJOR Brands are accurate up to 6 inches, after that machine is just guessing, because the signal is weakened in deeper targets and machine thinks of them as small targets with less depth rather than big objects with more depth . Question: (G.Sommi , Italy )Is it possible through metal detection techniques to determine not only if” there is metal but also how much” (mass or weight) metal is there? More precisely I would like to determine, in a volume of approximately two cubic meters of material, containing both magnetic (ferrous), and non-magnetic material, the amount of the former, by passing it through a metal detecting gate. Please let me know 1. If what requested is feasible 2. Which is the precision one may obtain in the weighing process 3. How much a metal detection gate able to solve the task may cost 4. If the possibility of getting data in digital form is included in the above price. Answer: I gave many thoughts to your question. This reminds me of a Greek scientist who was trying to obtain the purity of a Golden crown about 2500 years ago. He could measure the volume easily because of the known dimensions, but the question was its density. Since density is Mass over Volume, the only remaining part was the mass to measure. He found out that if any object is placed in a liquid, the weight of the object would decrease by the amount of the weight of the liquid replaced by the object. This lead him to measure the mass and of course, the density of the object which would lead him in the finding the purity of the crown.Of course, If someone could use that technique 2500 years ago, we can also use a similar technique using electromagnetic field instead of water or any liquid to measure the mass. What it comes to my mind is to place the metallic object in the center of a spherical box and make a coil with rotating around it in spherical path. Data could be continuously collected and analyzed by a microprocessor or a computer. The reason for rotation in spherical path is because we want to keep the distance of coil from the center of the mass as constant as possible for the best results. Now to find out about the magnetic and non-magnetic material, we can use different frequencies. Magnetic and non-magnetic objects behave differently when different frequencies are applied. Therefore, data collected again can be obtained and processed with a microprocessor. Let’s not to get confused, our objective is not to obtain the mass or weight, but it is to obtain the density or the percentage of the different mass (magnetic and non-magnetic). If we find the density (mass over volume) or percentage of the different mass, we can easily obtain the weight, since weight is equal to mass times g (=9.8 m/s/s). Regarding the cost of this project, I do not really know. We better off using the old method as described above instead.
Question: (Wesley Drennan) I am building a meter that will measure the intensity of a signal coming from a metal detector. I wish to display this signal on a 2x16 LCD display. What would the likely connection point to obtain the intensity of the signal. Transmitter signal? receiver signal? headphone plug?
Answer: You can get your input from the receiver, and you need to amplify the signal by a transistor or an op-amp. If you are trying to get your input from the speaker, it would work but you must be very careful for the following reasons. 1- If you use a headphone jack, the impedance of headphones are usually 32 ohm, while speakers are 8 ohms, therefore you better use a current divider (resistors) to prevent change is internal impedance of your input, since different resistance will result in different currents and then it will result in different readings. 2- If your battery goes low, your meter reading will go low too if speaker output is chosen. 3- If your circuit has discriminator , then the meter readings would be sharp and receiver (As an input) must be used instead. If BFO detector is used, input of the amplifier is the output of the Mixer. If balanced-bridge detector is used, the input of the amplifier is the output of the inductance bridge. If two-box, induction-balanced detector is used the input of amplifier is the output of the reciever's RF amp. Question: (Peter), Do you find machines with auto ground balance to be more accurate than machines that require you to ground balance manually? Answer: Manual ground balancing is more accurate, but not very practical since you need to ground balance it rapidly. It really depends on the type of machine. Usually coin shooting machines are better with automatic ground balancing because the size of coins are big enough to be distinguished. But when we are talking about soil mineralization and small nuggets, auto ground balancing is not as good as manual one, because we need to move the coil up and down or we can see the real nature of the soil for better adjustment. If you do metal detecting for a while, you will learn what the sounds mean to you. In conclusion, For coin and relic hunting auto ground balancing and for nugget shooting (Gold machines) manual ground balancing is recommended. Update: Tesoro's New Nugget Machine, Lobo Super Traq, Is the only U.S. Nugget machine that uses advance microprocessor design to automatically ground balance. This Design for the first time makes a nugget machine work properly combined with an auto ground balance system.