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Variable capacitors and semi variable capacitors

The information comes from:the Internet posted on:2023-06-27

Variable capacitors and semi variable capacitors
1、 Variable capacitor
A variable capacitor is a type of capacitor whose capacitance can be adjusted within a certain range, usually used as a tuning capacitor in radio reception circuits.
Variable capacitors can be divided into air dielectric variable capacitors and solid dielectric variable capacitors based on the dielectric materials used.
1. Air dielectric variable capacitor
The electrodes of an air dielectric variable capacitor are composed of two sets of metal sheets. The fixed group of two sets of electrodes is a fixed piece, and the group that can rotate is a moving piece. Air is used as the medium between the moving piece and the fixed piece. When the moving blades of an air dielectric variable capacitor are rotated so that they are all screwed between the fixed blades, its capacitance is the maximum; On the contrary, when all the moving pieces are rotated out of the fixed pieces, the capacitance is the smallest.
Air dielectric variable capacitors are divided into air single connected variable capacitors (referred to as air single connected variable capacitors) and air double connected variable capacitors (referred to as air double connected variable capacitors, which are composed of two sets of moving and fixed plates and can rotate synchronously on the same axis).
Air dielectric variable capacitors are generally used in radios, electronic instruments, high-frequency signal generators, communication equipment, and related electronic equipment
Commonly used domestic air single connected variable capacitors include CB-1- ××× Series and CB-X- ××× Series,
Commonly used air double connected variable capacitors include CB-2- ××× Series and CB-2X- ××× Series.
2. Solid dielectric variable capacitor: Solid dielectric variable capacitor is a type of capacitor that adds mica or plastic (polystyrene and other materials) film as the medium between its moving and fixed plates (both of which are irregular semi circular metal plates), and the outer shell is made of transparent plastic. Its advantages are small size and light weight; The disadvantage is loud noise and easy wear. Solid dielectric variable capacitors are divided into sealed single connected variable capacitors (referred to as sealed single connected capacitors), sealed double connected variable capacitors (referred to as sealed double connected capacitors, which have two sets of moving pieces, fixed pieces, and media that can rotate synchronously on the same axis), and sealed four connected variable capacitors (referred to as sealed four connected capacitors, which have four sets of moving pieces, fixed pieces, and media).
Sealed single connected variable capacitors are mainly used in simple radios or electronic instruments;
The sealed double connected variable capacitor is used in Transistor radio and related electronic instruments and equipment; Sealed four connected variable capacitors are commonly used in AM/FM multi band radios.
2、 Semi variable capacitor
Semi variable capacitors, also known as fine-tuning capacitors, are used as compensation capacitors or correction capacitors in various tuning and oscillation circuits. It is divided into various types, such as mica fine-tuning capacitors, ceramic dielectric fine-tuning capacitors, thin film fine-tuning capacitors, and pull wire fine-tuning capacitors.
1. Mica trimming capacitor: Mica trimming capacitor changes the capacitance by adjusting the distance between the screw and the fixed piece. The moving piece is an elastic copper or aluminum piece, while the fixed piece is a fixed metal piece, with a layer of mica thin film attached to its surface as the medium. Mica fine-tuning capacitors can be divided into single fine-tuning and double fine-tuning, and the capacitance can be repeatedly adjusted.
2. Ceramic fine tuning capacitors: Ceramic fine tuning capacitors use ceramics as the medium. A semi circular silver layer is coated on both the moving and fixed plates. By rotating the moving plate to change the distance between the two silver plates, the capacitance can be changed