Schematic diagram
Schematic diagram of the detector is presented in Fig. 2.42. Reference the generator of the metal detector is built on a capacitive treatacne on the transistor T1. Contour coil L1 is a sensor device. The capacitors C3-C6 are used to set the generator frequency to 50 kHz. Via the coupling capacitor C7 sinusoidal voltage from the generator enters the crystal filter.
Capacity C7 is small, thereby the effect of the subsequent stages in the operation the generator is practically impossible. A threshold device is assembled FET T2. Threshold voltage set divider R5-R7. Capacitor C8 smoothes pulsations on the indicator IP.
Fig. 2.42. Schematic diagram Kartavenko on two of the metal detector transistors
Filter R4C1 isolation exercises alternating current between the threshold and driving generators.
Sensor detector
The sensor of the detector consists of a rigid annular frame made Plexiglas, on which is wound with 65 turns of passage PEL of 0.2. The coil is enclosed in a shield of aluminum foil and filled with epoxy resin. The sensor is connected to the measuring unit coaxial cable RK-75.
Special attention should be paid to the workmanship of the metal detector. It should be light in weight, rigid and elastic. Otherwise, even with light the strikes are inevitable when working with the device in field conditions, the oscillator frequency "leaves" - metal upset. The base frame may serve as the annular frame Plexiglas or polystyrene d=300 mm Winding need to saarnisaari aluminum foil thickness of 0.05 mm.
To interconnect ends of the screen can not be, otherwise the cage formed round. The winding should be connected to the RC-75 cable length 0.3-1 m (braided cable to connect and also the screen coil). This place then you need to pour epoxy resin. The connection of the sensor with electronics should be permanent.
Capabilities and features the use of a metal detector
The detector has a very high sensitivity. Arrow indicator rejected by one unit, when the frame of the device is approaching an iron disk with a diameter of 13 cm at a distance of 80 cm And objects with a diameter of 3-5 cm give the same the deflection at a distance of 10-15 cm.
The device responds almost equally to any metal. So, for example, steel, aluminum and brass wheels provide equal distances, equal variances arrow. They do not depend on a solid object or a hollow.
When working with a metal detector must be considered background noise.
Sandy and peat soils, earth, wood, water background signal is not given. Therefore, the device works well in fresh water, in wooden buildings and nicamente soils. Gives a strong background brick (burnt clay has magnetic properties) and some minerals.
On the readings and affect the temperature change. Therefore, the frame is better to put it in a case of a thermal insulator, for example, Styrofoam. For under water sensor metal is first necessary to hold for 10-15 minutes in water and then configure the device.
Authors: A. Zakharov, V. Chikin