hello Teemo,
this concept is based on the damping proces patented by Ebinger
i made this summary from german to english, very simple by google translator
Model 1 Basic version
The attenuation-sensitive search oscillator of the metal detector is designed as an LC circuit and comprises a detector coil, a capacitor connected in parallel thereto, and other components. The output of the search oscillator is connected to a rectifier which generates a DC directional voltage from the amplitude of the search oscillator. The DC voltage or directional voltage of the rectifier is fed to a downstream amplifier which is designed as a DC voltage amplifier or DC amplifier. A voltage-frequency converter is connected to the output of the amplifier, by means of which the amplified DC directional voltage is converted into an acoustic signal, which is reproduced via a loudspeaker, which is connected to the output of the voltage-frequency converter 5. (The entire part could do a microcontroller).
In the presence of conductive objects, the amplitude of the attenuation sensitive oscillator becomes smaller, and this amplitude decrease is indicated by the loudspeaker.
Extension 1
When the conductive objects, such as metal or ferritic parts, are exposed, the operating frequency of the search oscillator also changes. In order to detect the frequency change of the search oscillator in the presence of a conductive object, a frequency comparator is provided whose input is supplied with the search oscillator signal, which is transmitted via a line from the search oscillator to the comparator. The comparator internally generates a reference frequency and compares this with the frequency of the search oscillator signal applied to the comparator input. A frequency increase (? F), i.e. a search oscillator frequency that is above the reference frequency, indicates the presence of a non-ferrous metal, while the negative comparison result (-? F) indicates the presence of an iron metal (Fe metal). An optical display device 11, which is designed, for example, as a zero instrument, is connected to an output of the comparator 8, with a pointer deflection in the positive direction indicating the presence of a non-ferrous metal and a deflection in the negative direction indicating the presence of an iron metal.
The last part can be a high or a low tone instead of plus or minus.
Extension 2
Furthermore, a signal modulator or frequency modulator is provided, which is connected to a further output of the frequency comparator for receiving the comparison result from the comparator. The output of the modulator is connected to the voltage-frequency converter and controls its input by modulating the acoustic signal generated in the device with the modulation signal of the modulator. For example, the modulator is designed as a frequency modulator and generates a control voltage as a function of the input signal, the frequency of which increases or decreases in accordance with the result of the frequency comparison performed in the frequency comparator. In this way, it is possible to distinguish acoustically between iron and non-ferrous metals via the loudspeaker.
Further information on the metal object detected by the metal detector is achieved according to the invention by a processing unit which processes the search oscillator frequency change with the search oscillator amplitude change due to the presence of a metal object.
The comparator has two inputs. One input of the comparator is connected to one output of the frequency comparator and the other input of the comparator is connected to the output of the amplifier. The comparator is designed to perform a comparison of the voltage level of the signal applied to the output of the amplifier (DC voltage signal) with a voltage signal from the frequency comparator which includes the frequency variation with respect to the reference frequency. In the comparator, the attenuation effect, ie the amplitude change with the frequency change in magnitude and direction, is compared with one another. This comparison result is displayed optically via a display which is connected to an output of the comparator and is also designed as a zero-line instrument.
For example, in the case of large search oscillator amplitude bursts, only small search oscillator frequency changes occur. This behavior, which is typical for a given object, allows conclusions to be drawn about the size, material properties and distance of the hidden object, and a corresponding evaluation is made via the comparator and displayed by the display.
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