En una situación de emergencia el profesional de la electrónica puede tener la necesidad de localizar una canalización metálica, un objeto de metal o incluso hilos incrustados o enterrados en el piso en una planta industrial. Una forma simple de improvisar un detector de metales es la que proponemos en este artículo.

Una forma simple de detectar objetos de metal es por la variación que la presencia de objetos metálicos causan en la inductancia de una bobina. Si esta bobina forma parte de un circuito resonante que determina la frecuencia de un oscilador, el efecto será obvio: la frecuencia generada va a cambiar.

Otra posibilidad de uso para el dispositivo es en la detección de objetos de metal que estén presentes en el interior de envases y no puedan ser abiertos para verificación. Una forma sencilla de detectar armas u otros objetos peligrosos.

Lo que proponemos con esta solución improvisada que puede ayudar al profesional que necesita localizar un objeto de metal enterrado o embutido es un oscilador que opera en el rango de ondas medias y que utiliza una bobina sensora en su circuito resonante.

El detector es una simple radio AM ubicada cerca del circuito. Sintoniza la frecuencia del oscilador en un punto libre de la banda y se recorre el lugar en que el metal debe ser detectado. En su presencia la frecuencia sintonizada "huye" lo que puede ser fácilmente percibido por el operador, como muestra la figura 1.

 


 

 

El circuito no es crítico, lo que significa que sus armónicos se pueden sintonizar y utilizar con facilidad y dependiendo de la bobina de objetos hasta algunas decenas de centímetros enterrados o incrustados, se pueden localizar.

En la figura 2 tenemos el circuito completo del oscilador que es alimentado por pilas comunes.

 


 

 

La placa de circuito impreso para este montaje se muestra en la figura 3.

 


 

 

La bobina está formada por 20 + 20 espiras de hilo 28 o más fino en una forma de plástico de 15 a 30 cm de diámetro. Una forma de pastel de plástico sirve perfectamente para ese propósito.

  Los capacitores deben ser cerámicos y el transistor admite equivalentes como el 2N2222, BF494, siempre que la disposición de las terminales sea observada.

El capacitor variable se puede obtener de cualquier radio AM transistorizada fuera de uso. Sólo tenga cuidado para utilizar la sección de AM y no FM para obtener una mayor gama de variaciones de frecuencias.

Para utilizar, basta con conectar el circuito, ajustar CV para que la señal sea captada en una frecuencia libre de la banda de AM, y acercar la bobina del lugar en que se desea investigar la presencia de metales. La fuga de la señal, indica la presencia de metal.

 

Q1 - BC548 o equivalente - transistores NPN de uso general

CV - Capacitor variable de radio AM

S1 - Interruptor simple

R1 - 22 k ohms x 1/8 W - resistor

C1 - 2,2 nF - capacitor de cerámica

C2 - 100 nF - capacitor de cerámica

B1 - 6 V - 4 pilas pequeñas

L1 - Ver texto

Varios: radio AM transistorizado, placa de circuito impreso, soporte de pilas, caja para montaje, hilos, soldadura, etc.

 

 

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