NON-INDUCTIVE COILS

Through the inductive is very useful property of a.c. circuits, but there are some electronic circuits in which the inductance is not desired at all. For example, when a wire wound resistor is used in a.c. circuits, it should have a non inductive winding. Besides, non-inductive coil the feeder line used for joining a transmitter or T.V. receiver to the antenna and the wire used for connecting indirectly heated filaments to the source of supply are designed to have minimum inductance. A twisted wire line of two parallel conductors’ line is used as feeder line.

INDUCTOR’S WINDING 

Various methods are used for winding the inductors so as to minimize the undesired capacitance between its turns. Principal winding methods are as follows:

1.       Solenoid-:

A solenoid is a single layered coil whose length is nearly 10 times of diameter.

2.       Toroid:

 It is a solenoid which is turned into a loop shape.

3.       Honeycomb Winding:

In this method the layers of winding take the shape of a honeycomb. The advantage of this method is this that the size of the coil can be made pretty small.

4.       Variometer:

A slight variation can be done with the help of dust or ferrite core in the inductance value of a coil but, when major variation is desired in the inductance value, a variometer is used. It consists of two coils wound on separate hallow cylindrical spools which are placed perpendicular to each other. When the two coils are perpendicular to each other, the inductance is minimum and when the two coils are parallel to each other, the inductance is maximum.