Magnetization indicator. Scheme, description

Magnetization indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

A conventional compass is sensitive to a magnetic field. It is enough to carry the magnetized end of the screwdriver in front of him, as the arrow deviates. But, unfortunately, after that the arrow will swing for a long time. Therefore, it is not always convenient to use such an indicator. The need for such a measuring device often arises.

The indicator assembled from several parts turns out to be completely non-inertial and relatively sensitive. For example, they can determine the magnetization of a razor blade or a watch screwdriver.

The principle of operation of the indicator is extremely simple: if a magnetized object is carried near the coil, then some EMF will appear on its terminals, which only needs to be amplified and applied to the indicator, for example, to a lamp from a flashlight.

Magnetization Indicator / Indicator Circuit
Fig.1. Schematic diagram of the magnetization indicator

Figure 1 shows a schematic diagram of the indicator. The sensor is an L1 coil wound on a steel core. It is connected through the capacitor C1 to the amplifying stage, made on the transistor VT1. The operation mode of the cascade is set by resistors R1 and R2. Depending on the parameters of the transistor, the optimal operating mode is set by a variable resistor R1.

A composite transistor VT2VT3 from transistors of different structures is included in the emitter circuit of the transistor of the first stage. The load of this transistor is the signal lamp HL1. To limit the maximum collector current of the transistor VT3, a resistor R2 is in the base circuit of the transistor VT3.

As a sensor, it is best to use a coil with a core from electromagnetic relays PCM, RES6, RES9 or others, with a winding resistance of at least 200 ohms. The greater the winding resistance, the more sensitive the indicator.

Details

Instead of the MP103A transistor, you can use the KT315 with any letter index. The main thing is that the collector reverse current is not too large. Instead of MP25B, any transistors of the MP25, MP26 series with a transfer coefficient of at least 40 are suitable. Capacitors - any, fixed resistors - MLT-0,25, variable resistor - SP-1. Signal lamp - for a voltage of 3,5 V and possibly a lower current, for example 0,15 A.

Establishment

After mounting the parts on the board or surface mounting and checking the correct connections, you can apply power. After that, you need to install the variable resistor engine so that the filament of the lamp barely glows. If the thread glows too brightly even when the slider is in the upper position according to the scheme, then the resistance of the resistor R2 is too low and its value needs to be increased. A permanent magnet is then briefly placed in front of the sensor core. The lamp should glow brightly. If the flash is weak, this indicates that the transfer coefficient of the transistor VT1 is too small. It will have to be replaced.

During the operation of the indicator with a variable resistor, first set the brightness of the lamp as low as possible, and then bring the object under test to the sensor core. When checking weakly magnetized objects, the initial brightness of the lamp should be slightly increased in order to better notice its change.

Literature

B. S. Ivanov, "Homemade young radio amateur", Moscow, DOSAAF USSR, 1988

Author: Alexander Shepetko, Lugansk, Ukraine; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Indicators, detectors, metal detectors.

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